\input texinfo @c -*-texinfo-*- @c %**start of header @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo @c o @c GNAT DOCUMENTATION o @c o @c G N A T _ U G N o @c o @c Copyright (C) 1992-2010, AdaCore o @c o @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo @setfilename gnat_ugn.info @copying Copyright @copyright{} 1995-2009 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. @end copying @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo @c @c GNAT_UGN Style Guide @c @c 1. Always put a @noindent on the line before the first paragraph @c after any of these commands: @c @c @chapter @c @section @c @subsection @c @subsubsection @c @subsubsubsection @c @c @end smallexample @c @end itemize @c @end enumerate @c @c 2. DO NOT use @example. Use @smallexample instead. @c a) DO NOT use highlighting commands (@b{}, @i{}) inside an @smallexample @c context. These can interfere with the readability of the texi @c source file. 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The unw flag covers topics for both Unix and @c Windows. @c @c oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo @set NOW January 2007 @c This flag is used where the text refers to conditions that exist when the @c text was entered into the document but which may change over time. @c Update the setting for the flag, and (if necessary) the text surrounding, @c the references to the flag, on future doc revisions: @c search for @value{NOW}. @set FSFEDITION @set EDITION GNAT @set DEFAULTLANGUAGEVERSION Ada 2005 @set NONDEFAULTLANGUAGEVERSION Ada 95 @ifset unw @set PLATFORM @end ifset @ifset vms @set PLATFORM OpenVMS @end ifset @c @ovar(ARG) @c ---------- @c The ARG is an optional argument. To be used for macro arguments in @c their documentation (@defmac). @macro ovar{varname} @r{[}@var{\varname\}@r{]}@c @end macro @c Status as of November 2009: @c Unfortunately texi2pdf and texi2html treat the trailing "@c" @c differently, and faulty output is produced by one or the other @c depending on whether the "@c" is present or absent. @c As a result, the @ovar macro is not used, and all invocations @c of the @ovar macro have been expanded inline. @settitle @value{EDITION} User's Guide @value{PLATFORM} @dircategory GNU Ada tools @direntry * @value{EDITION} User's Guide: (gnat_ugn). @value{PLATFORM} @end direntry @include gcc-common.texi @setchapternewpage odd @syncodeindex fn cp @c %**end of header @titlepage @title @value{EDITION} User's Guide @ifset vms @sp 1 @flushright @titlefont{@i{@value{PLATFORM}}} @end flushright @end ifset @sp 2 @subtitle GNAT, The GNU Ada Compiler @versionsubtitle @author AdaCore @page @vskip 0pt plus 1filll @insertcopying @end titlepage @ifnottex @node Top, About This Guide, (dir), (dir) @top @value{EDITION} User's Guide @noindent @value{EDITION} User's Guide @value{PLATFORM} @noindent GNAT, The GNU Ada Compiler@* GCC version @value{version-GCC}@* @noindent AdaCore@* @menu * About This Guide:: * Getting Started with GNAT:: * The GNAT Compilation Model:: * Compiling Using gcc:: * Binding Using gnatbind:: * Linking Using gnatlink:: * The GNAT Make Program gnatmake:: * Improving Performance:: * Renaming Files Using gnatchop:: * Configuration Pragmas:: * Handling Arbitrary File Naming Conventions Using gnatname:: * GNAT Project Manager:: * Tools Supporting Project Files:: * The Cross-Referencing Tools gnatxref and gnatfind:: * The GNAT Pretty-Printer gnatpp:: * The GNAT Metric Tool gnatmetric:: * File Name Krunching Using gnatkr:: * Preprocessing Using gnatprep:: * The GNAT Library Browser gnatls:: * Cleaning Up Using gnatclean:: @ifclear vms * GNAT and Libraries:: * Using the GNU make Utility:: @end ifclear * Memory Management Issues:: * Stack Related Facilities:: * Verifying Properties Using gnatcheck:: * Creating Sample Bodies Using gnatstub:: * Generating Ada Bindings for C and C++ headers:: * Other Utility Programs:: * Running and Debugging Ada Programs:: @ifclear vms * Code Coverage and Profiling:: @end ifclear @ifset vms * Compatibility with HP Ada:: @end ifset * Platform-Specific Information for the Run-Time Libraries:: * Example of Binder Output File:: * Elaboration Order Handling in GNAT:: * Conditional Compilation:: * Inline Assembler:: * Compatibility and Porting Guide:: @ifset unw * Microsoft Windows Topics:: @end ifset * GNU Free Documentation License:: * Index:: --- The Detailed Node Listing --- About This Guide * What This Guide Contains:: * What You Should Know before Reading This Guide:: * Related Information:: * Conventions:: Getting Started with GNAT * Running GNAT:: * Running a Simple Ada Program:: * Running a Program with Multiple Units:: * Using the gnatmake Utility:: @ifset vms * Editing with Emacs:: @end ifset @ifclear vms * Introduction to GPS:: @end ifclear The GNAT Compilation Model * Source Representation:: * Foreign Language Representation:: * File Naming Rules:: * Using Other File Names:: * Alternative File Naming Schemes:: * Generating Object Files:: * Source Dependencies:: * The Ada Library Information Files:: * Binding an Ada Program:: * Mixed Language Programming:: @ifclear vms * Building Mixed Ada & C++ Programs:: * Comparison between GNAT and C/C++ Compilation Models:: @end ifclear * Comparison between GNAT and Conventional Ada Library Models:: @ifset vms * Placement of temporary files:: @end ifset Foreign Language Representation * Latin-1:: * Other 8-Bit Codes:: * Wide Character Encodings:: Compiling Ada Programs With gcc * Compiling Programs:: * Switches for gcc:: * Search Paths and the Run-Time Library (RTL):: * Order of Compilation Issues:: * Examples:: Switches for gcc * Output and Error Message Control:: * Warning Message Control:: * Debugging and Assertion Control:: * Validity Checking:: * Style Checking:: * Run-Time Checks:: * Using gcc for Syntax Checking:: * Using gcc for Semantic Checking:: * Compiling Different Versions of Ada:: * Character Set Control:: * File Naming Control:: * Subprogram Inlining Control:: * Auxiliary Output Control:: * Debugging Control:: * Exception Handling Control:: * Units to Sources Mapping Files:: * Integrated Preprocessing:: @ifset vms * Return Codes:: @end ifset Binding Ada Programs With gnatbind * Running gnatbind:: * Switches for gnatbind:: * Command-Line Access:: * Search Paths for gnatbind:: * Examples of gnatbind Usage:: Switches for gnatbind * Consistency-Checking Modes:: * Binder Error Message Control:: * Elaboration Control:: * Output Control:: * Binding with Non-Ada Main Programs:: * Binding Programs with No Main Subprogram:: Linking Using gnatlink * Running gnatlink:: * Switches for gnatlink:: The GNAT Make Program gnatmake * Running gnatmake:: * Switches for gnatmake:: * Mode Switches for gnatmake:: * Notes on the Command Line:: * How gnatmake Works:: * Examples of gnatmake Usage:: Improving Performance * Performance Considerations:: * Text_IO Suggestions:: * Reducing Size of Ada Executables with gnatelim:: * Reducing Size of Executables with unused subprogram/data elimination:: Performance Considerations * Controlling Run-Time Checks:: * Use of Restrictions:: * Optimization Levels:: * Debugging Optimized Code:: * Inlining of Subprograms:: * Other Optimization Switches:: * Optimization and Strict Aliasing:: @ifset vms * Coverage Analysis:: @end ifset Reducing Size of Ada Executables with gnatelim * About gnatelim:: * Running gnatelim:: * Processing Precompiled Libraries:: * Correcting the List of Eliminate Pragmas:: * Making Your Executables Smaller:: * Summary of the gnatelim Usage Cycle:: Reducing Size of Executables with unused subprogram/data elimination * About unused subprogram/data elimination:: * Compilation options:: Renaming Files Using gnatchop * Handling Files with Multiple Units:: * Operating gnatchop in Compilation Mode:: * Command Line for gnatchop:: * Switches for gnatchop:: * Examples of gnatchop Usage:: Configuration Pragmas * Handling of Configuration Pragmas:: * The Configuration Pragmas Files:: Handling Arbitrary File Naming Conventions Using gnatname * Arbitrary File Naming Conventions:: * Running gnatname:: * Switches for gnatname:: * Examples of gnatname Usage:: The Cross-Referencing Tools gnatxref and gnatfind * Switches for gnatxref:: * Switches for gnatfind:: * Project Files for gnatxref and gnatfind:: * Regular Expressions in gnatfind and gnatxref:: * Examples of gnatxref Usage:: * Examples of gnatfind Usage:: The GNAT Pretty-Printer gnatpp * Switches for gnatpp:: * Formatting Rules:: The GNAT Metrics Tool gnatmetric * Switches for gnatmetric:: File Name Krunching Using gnatkr * About gnatkr:: * Using gnatkr:: * Krunching Method:: * Examples of gnatkr Usage:: Preprocessing Using gnatprep * Preprocessing Symbols:: * Using gnatprep:: * Switches for gnatprep:: * Form of Definitions File:: * Form of Input Text for gnatprep:: The GNAT Library Browser gnatls * Running gnatls:: * Switches for gnatls:: * Examples of gnatls Usage:: Cleaning Up Using gnatclean * Running gnatclean:: * Switches for gnatclean:: @c * Examples of gnatclean Usage:: @ifclear vms GNAT and Libraries * Introduction to Libraries in GNAT:: * General Ada Libraries:: * Stand-alone Ada Libraries:: * Rebuilding the GNAT Run-Time Library:: Using the GNU make Utility * Using gnatmake in a Makefile:: * Automatically Creating a List of Directories:: * Generating the Command Line Switches:: * Overcoming Command Line Length Limits:: @end ifclear Memory Management Issues * Some Useful Memory Pools:: * The GNAT Debug Pool Facility:: @ifclear vms * The gnatmem Tool:: @end ifclear Stack Related Facilities * Stack Overflow Checking:: * Static Stack Usage Analysis:: * Dynamic Stack Usage Analysis:: Some Useful Memory Pools The GNAT Debug Pool Facility @ifclear vms The gnatmem Tool * Running gnatmem:: * Switches for gnatmem:: * Example of gnatmem Usage:: @end ifclear Verifying Properties Using gnatcheck * Format of the Report File:: * General gnatcheck Switches:: * gnatcheck Rule Options:: * Adding the Results of Compiler Checks to gnatcheck Output:: * Project-Wide Checks:: * Rule exemption:: * Predefined Rules:: * Example of gnatcheck Usage:: Sample Bodies Using gnatstub * Running gnatstub:: * Switches for gnatstub:: Other Utility Programs * Using Other Utility Programs with GNAT:: * The External Symbol Naming Scheme of GNAT:: * Converting Ada Files to html with gnathtml:: @ifclear vms Code Coverage and Profiling * Code Coverage of Ada Programs using gcov:: * Profiling an Ada Program using gprof:: @end ifclear Running and Debugging Ada Programs * The GNAT Debugger GDB:: * Running GDB:: * Introduction to GDB Commands:: * Using Ada Expressions:: * Calling User-Defined Subprograms:: * Using the Next Command in a Function:: * Ada Exceptions:: * Ada Tasks:: * Debugging Generic Units:: * Remote Debugging using gdbserver:: * GNAT Abnormal Termination or Failure to Terminate:: * Naming Conventions for GNAT Source Files:: * Getting Internal Debugging Information:: * Stack Traceback:: @ifset vms * LSE:: @end ifset @ifset vms Compatibility with HP Ada * Ada Language Compatibility:: * Differences in the Definition of Package System:: * Language-Related Features:: * The Package STANDARD:: * The Package SYSTEM:: * Tasking and Task-Related Features:: * Pragmas and Pragma-Related Features:: * Library of Predefined Units:: * Bindings:: * Main Program Definition:: * Implementation-Defined Attributes:: * Compiler and Run-Time Interfacing:: * Program Compilation and Library Management:: * Input-Output:: * Implementation Limits:: * Tools and Utilities:: Language-Related Features * Integer Types and Representations:: * Floating-Point Types and Representations:: * Pragmas Float_Representation and Long_Float:: * Fixed-Point Types and Representations:: * Record and Array Component Alignment:: * Address Clauses:: * Other Representation Clauses:: Tasking and Task-Related Features * Implementation of Tasks in HP Ada for OpenVMS Alpha Systems:: * Assigning Task IDs:: * Task IDs and Delays:: * Task-Related Pragmas:: * Scheduling and Task Priority:: * The Task Stack:: * External Interrupts:: Pragmas and Pragma-Related Features * Restrictions on the Pragma INLINE:: * Restrictions on the Pragma INTERFACE:: * Restrictions on the Pragma SYSTEM_NAME:: Library of Predefined Units * Changes to DECLIB:: Bindings * Shared Libraries and Options Files:: * Interfaces to C:: @end ifset Platform-Specific Information for the Run-Time Libraries * Summary of Run-Time Configurations:: * Specifying a Run-Time Library:: * Choosing the Scheduling Policy:: * Solaris-Specific Considerations:: * Linux-Specific Considerations:: * AIX-Specific Considerations:: * Irix-Specific Considerations:: * RTX-Specific Considerations:: * HP-UX-Specific Considerations:: Example of Binder Output File Elaboration Order Handling in GNAT * Elaboration Code:: * Checking the Elaboration Order:: * Controlling the Elaboration Order:: * Controlling Elaboration in GNAT - Internal Calls:: * Controlling Elaboration in GNAT - External Calls:: * Default Behavior in GNAT - Ensuring Safety:: * Treatment of Pragma Elaborate:: * Elaboration Issues for Library Tasks:: * Mixing Elaboration Models:: * What to Do If the Default Elaboration Behavior Fails:: * Elaboration for Access-to-Subprogram Values:: * Summary of Procedures for Elaboration Control:: * Other Elaboration Order Considerations:: Conditional Compilation * Use of Boolean Constants:: * Debugging - A Special Case:: * Conditionalizing Declarations:: * Use of Alternative Implementations:: * Preprocessing:: Inline Assembler * Basic Assembler Syntax:: * A Simple Example of Inline Assembler:: * Output Variables in Inline Assembler:: * Input Variables in Inline Assembler:: * Inlining Inline Assembler Code:: * Other Asm Functionality:: Compatibility and Porting Guide * Compatibility with Ada 83:: * Compatibility between Ada 95 and Ada 2005:: * Implementation-dependent characteristics:: @ifclear vms @c This brief section is only in the non-VMS version @c The complete chapter on HP Ada issues is in the VMS version * Compatibility with HP Ada 83:: @end ifclear * Compatibility with Other Ada Systems:: * Representation Clauses:: @ifset vms * Transitioning to 64-Bit GNAT for OpenVMS:: @end ifset @ifset unw Microsoft Windows Topics * Using GNAT on Windows:: * CONSOLE and WINDOWS subsystems:: * Temporary Files:: * Mixed-Language Programming on Windows:: * Windows Calling Conventions:: * Introduction to Dynamic Link Libraries (DLLs):: * Using DLLs with GNAT:: * Building DLLs with GNAT:: * GNAT and Windows Resources:: * Debugging a DLL:: * Setting Stack Size from gnatlink:: * Setting Heap Size from gnatlink:: @end ifset * Index:: @end menu @end ifnottex @node About This Guide @unnumbered About This Guide @noindent @ifset vms This guide describes the use of @value{EDITION}, a compiler and software development toolset for the full Ada programming language, implemented on OpenVMS for HP's Alpha and Integrity server (I64) platforms. @end ifset @ifclear vms This guide describes the use of @value{EDITION}, a compiler and software development toolset for the full Ada programming language. @end ifclear It documents the features of the compiler and tools, and explains how to use them to build Ada applications. @value{EDITION} implements Ada 95 and Ada 2005, and it may also be invoked in Ada 83 compatibility mode. By default, @value{EDITION} assumes @value{DEFAULTLANGUAGEVERSION}, but you can override with a compiler switch (@pxref{Compiling Different Versions of Ada}) to explicitly specify the language version. Throughout this manual, references to ``Ada'' without a year suffix apply to both the Ada 95 and Ada 2005 versions of the language. @ifclear FSFEDITION For ease of exposition, ``@value{EDITION}'' will be referred to simply as ``GNAT'' in the remainder of this document. @end ifclear @menu * What This Guide Contains:: * What You Should Know before Reading This Guide:: * Related Information:: * Conventions:: @end menu @node What This Guide Contains @unnumberedsec What This Guide Contains @noindent This guide contains the following chapters: @itemize @bullet @item @ref{Getting Started with GNAT}, describes how to get started compiling and running Ada programs with the GNAT Ada programming environment. @item @ref{The GNAT Compilation Model}, describes the compilation model used by GNAT. @item @ref{Compiling Using gcc}, describes how to compile Ada programs with @command{gcc}, the Ada compiler. @item @ref{Binding Using gnatbind}, describes how to perform binding of Ada programs with @code{gnatbind}, the GNAT binding utility. @item @ref{Linking Using gnatlink}, describes @command{gnatlink}, a program that provides for linking using the GNAT run-time library to construct a program. @command{gnatlink} can also incorporate foreign language object units into the executable. @item @ref{The GNAT Make Program gnatmake}, describes @command{gnatmake}, a utility that automatically determines the set of sources needed by an Ada compilation unit, and executes the necessary compilations binding and link. @item @ref{Improving Performance}, shows various techniques for making your Ada program run faster or take less space. It discusses the effect of the compiler's optimization switch and also describes the @command{gnatelim} tool and unused subprogram/data elimination. @item @ref{Renaming Files Using gnatchop}, describes @code{gnatchop}, a utility that allows you to preprocess a file that contains Ada source code, and split it into one or more new files, one for each compilation unit. @item @ref{Configuration Pragmas}, describes the configuration pragmas handled by GNAT. @item @ref{Handling Arbitrary File Naming Conventions Using gnatname}, shows how to override the default GNAT file naming conventions, either for an individual unit or globally. @item @ref{GNAT Project Manager}, describes how to use project files to organize large projects. @item @ref{The Cross-Referencing Tools gnatxref and gnatfind}, discusses @code{gnatxref} and @code{gnatfind}, two tools that provide an easy way to navigate through sources. @item @ref{The GNAT Pretty-Printer gnatpp}, shows how to produce a reformatted version of an Ada source file with control over casing, indentation, comment placement, and other elements of program presentation style. @item @ref{The GNAT Metric Tool gnatmetric}, shows how to compute various metrics for an Ada source file, such as the number of types and subprograms, and assorted complexity measures. @item @ref{File Name Krunching Using gnatkr}, describes the @code{gnatkr} file name krunching utility, used to handle shortened file names on operating systems with a limit on the length of names. @item @ref{Preprocessing Using gnatprep}, describes @code{gnatprep}, a preprocessor utility that allows a single source file to be used to generate multiple or parameterized source files by means of macro substitution. @item @ref{The GNAT Library Browser gnatls}, describes @code{gnatls}, a utility that displays information about compiled units, including dependences on the corresponding sources files, and consistency of compilations. @item @ref{Cleaning Up Using gnatclean}, describes @code{gnatclean}, a utility to delete files that are produced by the compiler, binder and linker. @ifclear vms @item @ref{GNAT and Libraries}, describes the process of creating and using Libraries with GNAT. It also describes how to recompile the GNAT run-time library. @item @ref{Using the GNU make Utility}, describes some techniques for using the GNAT toolset in Makefiles. @end ifclear @item @ref{Memory Management Issues}, describes some useful predefined storage pools and in particular the GNAT Debug Pool facility, which helps detect incorrect memory references. @ifclear vms It also describes @command{gnatmem}, a utility that monitors dynamic allocation and deallocation and helps detect ``memory leaks''. @end ifclear @item @ref{Stack Related Facilities}, describes some useful tools associated with stack checking and analysis. @item @ref{Verifying Properties Using gnatcheck}, discusses @code{gnatcheck}, a utility that checks Ada code against a set of rules. @item @ref{Creating Sample Bodies Using gnatstub}, discusses @code{gnatstub}, a utility that generates empty but compilable bodies for library units. @item @ref{Generating Ada Bindings for C and C++ headers}, describes how to generate automatically Ada bindings from C and C++ headers. @item @ref{Other Utility Programs}, discusses several other GNAT utilities, including @code{gnathtml}. @ifclear vms @item @ref{Code Coverage and Profiling}, describes how to perform a structural coverage and profile the execution of Ada programs. @end ifclear @item @ref{Running and Debugging Ada Programs}, describes how to run and debug Ada programs. @ifset vms @item @ref{Compatibility with HP Ada}, details the compatibility of GNAT with HP Ada 83 @footnote{``HP Ada'' refers to the legacy product originally developed by Digital Equipment Corporation and currently supported by HP.} for OpenVMS Alpha. This product was formerly known as DEC Ada, @cindex DEC Ada and for historical compatibility reasons, the relevant libraries still use the DEC prefix. @end ifset @item @ref{Platform-Specific Information for the Run-Time Libraries}, describes the various run-time libraries supported by GNAT on various platforms and explains how to choose a particular library. @item @ref{Example of Binder Output File}, shows the source code for the binder output file for a sample program. @item @ref{Elaboration Order Handling in GNAT}, describes how GNAT helps you deal with elaboration order issues. @item @ref{Conditional Compilation}, describes how to model conditional compilation, both with Ada in general and with GNAT facilities in particular. @item @ref{Inline Assembler}, shows how to use the inline assembly facility in an Ada program. @item @ref{Compatibility and Porting Guide}, contains sections on compatibility of GNAT with other Ada development environments (including Ada 83 systems), to assist in porting code from those environments. @ifset unw @item @ref{Microsoft Windows Topics}, presents information relevant to the Microsoft Windows platform. @end ifset @end itemize @c ************************************************* @node What You Should Know before Reading This Guide @c ************************************************* @unnumberedsec What You Should Know before Reading This Guide @cindex Ada 95 Language Reference Manual @cindex Ada 2005 Language Reference Manual @noindent This guide assumes a basic familiarity with the Ada 95 language, as described in the International Standard ANSI/ISO/IEC-8652:1995, January 1995. It does not require knowledge of the new features introduced by Ada 2005, (officially known as ISO/IEC 8652:1995 with Technical Corrigendum 1 and Amendment 1). Both reference manuals are included in the GNAT documentation package. @node Related Information @unnumberedsec Related Information @noindent For further information about related tools, refer to the following documents: @itemize @bullet @item @xref{Top, GNAT Reference Manual, About This Guide, gnat_rm, GNAT Reference Manual}, which contains all reference material for the GNAT implementation of Ada. @ifset unw @item @cite{Using the GNAT Programming Studio}, which describes the GPS Integrated Development Environment. @item @cite{GNAT Programming Studio Tutorial}, which introduces the main GPS features through examples. @end ifset @item @cite{Ada 95 Reference Manual}, which contains reference material for the Ada 95 programming language. @item @cite{Ada 2005 Reference Manual}, which contains reference material for the Ada 2005 programming language. @item @xref{Top,, Debugging with GDB, gdb, Debugging with GDB}, @ifset vms in the GNU:[DOCS] directory, @end ifset for all details on the use of the GNU source-level debugger. @item @xref{Top,, The extensible self-documenting text editor, emacs, GNU Emacs Manual}, @ifset vms located in the GNU:[DOCS] directory if the EMACS kit is installed, @end ifset for full information on the extensible editor and programming environment Emacs. @end itemize @c ************** @node Conventions @unnumberedsec Conventions @cindex Conventions @cindex Typographical conventions @noindent Following are examples of the typographical and graphic conventions used in this guide: @itemize @bullet @item @code{Functions}, @command{utility program names}, @code{standard names}, and @code{classes}. @item @option{Option flags} @item @file{File names}, @samp{button names}, and @samp{field names}. @item @code{Variables}, @env{environment variables}, and @var{metasyntactic variables}. @item @emph{Emphasis}. @item @r{[}optional information or parameters@r{]} @item Examples are described by text @smallexample and then shown this way. @end smallexample @end itemize @noindent Commands that are entered by the user are preceded in this manual by the characters @w{``@code{$ }''} (dollar sign followed by space). If your system uses this sequence as a prompt, then the commands will appear exactly as you see them in the manual. If your system uses some other prompt, then the command will appear with the @code{$} replaced by whatever prompt character you are using. @ifset unw Full file names are shown with the ``@code{/}'' character as the directory separator; e.g., @file{parent-dir/subdir/myfile.adb}. If you are using GNAT on a Windows platform, please note that the ``@code{\}'' character should be used instead. @end ifset @c **************************** @node Getting Started with GNAT @chapter Getting Started with GNAT @noindent This chapter describes some simple ways of using GNAT to build executable Ada programs. @ifset unw @ref{Running GNAT}, through @ref{Using the gnatmake Utility}, show how to use the command line environment. @ref{Introduction to GPS}, provides a brief introduction to the GNAT Programming Studio, a visually-oriented Integrated Development Environment for GNAT. GPS offers a graphical ``look and feel'', support for development in other programming languages, comprehensive browsing features, and many other capabilities. For information on GPS please refer to @cite{Using the GNAT Programming Studio}. @end ifset @menu * Running GNAT:: * Running a Simple Ada Program:: * Running a Program with Multiple Units:: * Using the gnatmake Utility:: @ifset vms * Editing with Emacs:: @end ifset @ifclear vms * Introduction to GPS:: @end ifclear @end menu @node Running GNAT @section Running GNAT @noindent Three steps are needed to create an executable file from an Ada source file: @enumerate @item The source file(s) must be compiled. @item The file(s) must be bound using the GNAT binder. @item All appropriate object files must be linked to produce an executable. @end enumerate @noindent All three steps are most commonly handled by using the @command{gnatmake} utility program that, given the name of the main program, automatically performs the necessary compilation, binding and linking steps. @node Running a Simple Ada Program @section Running a Simple Ada Program @noindent Any text editor may be used to prepare an Ada program. (If @code{Emacs} is used, the optional Ada mode may be helpful in laying out the program.) The program text is a normal text file. We will assume in our initial example that you have used your editor to prepare the following standard format text file: @smallexample @c ada @cartouche with Ada.Text_IO; use Ada.Text_IO; procedure Hello is begin Put_Line ("Hello WORLD!"); end Hello; @end cartouche @end smallexample @noindent This file should be named @file{hello.adb}. With the normal default file naming conventions, GNAT requires that each file contain a single compilation unit whose file name is the unit name, with periods replaced by hyphens; the extension is @file{ads} for a spec and @file{adb} for a body. You can override this default file naming convention by use of the special pragma @code{Source_File_Name} (@pxref{Using Other File Names}). Alternatively, if you want to rename your files according to this default convention, which is probably more convenient if you will be using GNAT for all your compilations, then the @code{gnatchop} utility can be used to generate correctly-named source files (@pxref{Renaming Files Using gnatchop}). You can compile the program using the following command (@code{$} is used as the command prompt in the examples in this document): @smallexample $ gcc -c hello.adb @end smallexample @noindent @command{gcc} is the command used to run the compiler. This compiler is capable of compiling programs in several languages, including Ada and C. It assumes that you have given it an Ada program if the file extension is either @file{.ads} or @file{.adb}, and it will then call the GNAT compiler to compile the specified file. @ifclear vms The @option{-c} switch is required. It tells @command{gcc} to only do a compilation. (For C programs, @command{gcc} can also do linking, but this capability is not used directly for Ada programs, so the @option{-c} switch must always be present.) @end ifclear This compile command generates a file @file{hello.o}, which is the object file corresponding to your Ada program. It also generates an ``Ada Library Information'' file @file{hello.ali}, which contains additional information used to check that an Ada program is consistent. To build an executable file, use @code{gnatbind} to bind the program and @command{gnatlink} to link it. The argument to both @code{gnatbind} and @command{gnatlink} is the name of the @file{ALI} file, but the default extension of @file{.ali} can be omitted. This means that in the most common case, the argument is simply the name of the main program: @smallexample $ gnatbind hello $ gnatlink hello @end smallexample @noindent A simpler method of carrying out these steps is to use @command{gnatmake}, a master program that invokes all the required compilation, binding and linking tools in the correct order. In particular, @command{gnatmake} automatically recompiles any sources that have been modified since they were last compiled, or sources that depend on such modified sources, so that ``version skew'' is avoided. @cindex Version skew (avoided by @command{gnatmake}) @smallexample $ gnatmake hello.adb @end smallexample @noindent The result is an executable program called @file{hello}, which can be run by entering: @smallexample $ ^hello^RUN HELLO^ @end smallexample @noindent assuming that the current directory is on the search path for executable programs. @noindent and, if all has gone well, you will see @smallexample Hello WORLD! @end smallexample @noindent appear in response to this command. @c **************************************** @node Running a Program with Multiple Units @section Running a Program with Multiple Units @noindent Consider a slightly more complicated example that has three files: a main program, and the spec and body of a package: @smallexample @c ada @cartouche @group package Greetings is procedure Hello; procedure Goodbye; end Greetings; with Ada.Text_IO; use Ada.Text_IO; package body Greetings is procedure Hello is begin Put_Line ("Hello WORLD!"); end Hello; procedure Goodbye is begin Put_Line ("Goodbye WORLD!"); end Goodbye; end Greetings; @end group @group with Greetings; procedure Gmain is begin Greetings.Hello; Greetings.Goodbye; end Gmain; @end group @end cartouche @end smallexample @noindent Following the one-unit-per-file rule, place this program in the following three separate files: @table @file @item greetings.ads spec of package @code{Greetings} @item greetings.adb body of package @code{Greetings} @item gmain.adb body of main program @end table @noindent To build an executable version of this program, we could use four separate steps to compile, bind, and link the program, as follows: @smallexample $ gcc -c gmain.adb $ gcc -c greetings.adb $ gnatbind gmain $ gnatlink gmain @end smallexample @noindent Note that there is no required order of compilation when using GNAT. In particular it is perfectly fine to compile the main program first. Also, it is not necessary to compile package specs in the case where there is an accompanying body; you only need to compile the body. If you want to submit these files to the compiler for semantic checking and not code generation, then use the @option{-gnatc} switch: @smallexample $ gcc -c greetings.ads -gnatc @end smallexample @noindent Although the compilation can be done in separate steps as in the above example, in practice it is almost always more convenient to use the @command{gnatmake} tool. All you need to know in this case is the name of the main program's source file. The effect of the above four commands can be achieved with a single one: @smallexample $ gnatmake gmain.adb @end smallexample @noindent In the next section we discuss the advantages of using @command{gnatmake} in more detail. @c ***************************** @node Using the gnatmake Utility @section Using the @command{gnatmake} Utility @noindent If you work on a program by compiling single components at a time using @command{gcc}, you typically keep track of the units you modify. In order to build a consistent system, you compile not only these units, but also any units that depend on the units you have modified. For example, in the preceding case, if you edit @file{gmain.adb}, you only need to recompile that file. But if you edit @file{greetings.ads}, you must recompile both @file{greetings.adb} and @file{gmain.adb}, because both files contain units that depend on @file{greetings.ads}. @code{gnatbind} will warn you if you forget one of these compilation steps, so that it is impossible to generate an inconsistent program as a result of forgetting to do a compilation. Nevertheless it is tedious and error-prone to keep track of dependencies among units. One approach to handle the dependency-bookkeeping is to use a makefile. However, makefiles present maintenance problems of their own: if the dependencies change as you change the program, you must make sure that the makefile is kept up-to-date manually, which is also an error-prone process. The @command{gnatmake} utility takes care of these details automatically. Invoke it using either one of the following forms: @smallexample $ gnatmake gmain.adb $ gnatmake ^gmain^GMAIN^ @end smallexample @noindent The argument is the name of the file containing the main program; you may omit the extension. @command{gnatmake} examines the environment, automatically recompiles any files that need recompiling, and binds and links the resulting set of object files, generating the executable file, @file{^gmain^GMAIN.EXE^}. In a large program, it can be extremely helpful to use @command{gnatmake}, because working out by hand what needs to be recompiled can be difficult. Note that @command{gnatmake} takes into account all the Ada rules that establish dependencies among units. These include dependencies that result from inlining subprogram bodies, and from generic instantiation. Unlike some other Ada make tools, @command{gnatmake} does not rely on the dependencies that were found by the compiler on a previous compilation, which may possibly be wrong when sources change. @command{gnatmake} determines the exact set of dependencies from scratch each time it is run. @ifset vms @node Editing with Emacs @section Editing with Emacs @cindex Emacs @noindent Emacs is an extensible self-documenting text editor that is available in a separate VMSINSTAL kit. Invoke Emacs by typing @kbd{Emacs} at the command prompt. To get started, click on the Emacs Help menu and run the Emacs Tutorial. In a character cell terminal, Emacs help is invoked with @kbd{Ctrl-h} (also written as @kbd{C-h}), and the tutorial by @kbd{C-h t}. Documentation on Emacs and other tools is available in Emacs under the pull-down menu button: @code{Help - Info}. After selecting @code{Info}, use the middle mouse button to select a topic (e.g.@: Emacs). In a character cell terminal, do @kbd{C-h i} to invoke info, and then @kbd{m} (stands for menu) followed by the menu item desired, as in @kbd{m Emacs}, to get to the Emacs manual. Help on Emacs is also available by typing @kbd{HELP EMACS} at the DCL command prompt. The tutorial is highly recommended in order to learn the intricacies of Emacs, which is sufficiently extensible to provide for a complete programming environment and shell for the sophisticated user. @end ifset @ifclear vms @node Introduction to GPS @section Introduction to GPS @cindex GPS (GNAT Programming Studio) @cindex GNAT Programming Studio (GPS) @noindent Although the command line interface (@command{gnatmake}, etc.) alone is sufficient, a graphical Interactive Development Environment can make it easier for you to compose, navigate, and debug programs. This section describes the main features of GPS (``GNAT Programming Studio''), the GNAT graphical IDE. You will see how to use GPS to build and debug an executable, and you will also learn some of the basics of the GNAT ``project'' facility. GPS enables you to do much more than is presented here; e.g., you can produce a call graph, interface to a third-party Version Control System, and inspect the generated assembly language for a program. Indeed, GPS also supports languages other than Ada. Such additional information, and an explanation of all of the GPS menu items. may be found in the on-line help, which includes a user's guide and a tutorial (these are also accessible from the GNAT startup menu). @menu * Building a New Program with GPS:: * Simple Debugging with GPS:: @end menu @node Building a New Program with GPS @subsection Building a New Program with GPS @noindent GPS invokes the GNAT compilation tools using information contained in a @emph{project} (also known as a @emph{project file}): a collection of properties such as source directories, identities of main subprograms, tool switches, etc., and their associated values. See @ref{GNAT Project Manager} for details. In order to run GPS, you will need to either create a new project or else open an existing one. This section will explain how you can use GPS to create a project, to associate Ada source files with a project, and to build and run programs. @enumerate @item @emph{Creating a project} Invoke GPS, either from the command line or the platform's IDE. After it starts, GPS will display a ``Welcome'' screen with three radio buttons: @itemize @bullet @item @code{Start with default project in directory} @item @code{Create new project with wizard} @item @code{Open existing project} @end itemize @noindent Select @code{Create new project with wizard} and press @code{OK}. A new window will appear. In the text box labeled with @code{Enter the name of the project to create}, type @file{sample} as the project name. In the next box, browse to choose the directory in which you would like to create the project file. After selecting an appropriate directory, press @code{Forward}. A window will appear with the title @code{Version Control System Configuration}. Simply press @code{Forward}. A window will appear with the title @code{Please select the source directories for this project}. The directory that you specified for the project file will be selected by default as the one to use for sources; simply press @code{Forward}. A window will appear with the title @code{Please select the build directory for this project}. The directory that you specified for the project file will be selected by default for object files and executables; simply press @code{Forward}. A window will appear with the title @code{Please select the main units for this project}. You will supply this information later, after creating the source file. Simply press @code{Forward} for now. A window will appear with the title @code{Please select the switches to build the project}. Press @code{Apply}. This will create a project file named @file{sample.prj} in the directory that you had specified. @item @emph{Creating and saving the source file} After you create the new project, a GPS window will appear, which is partitioned into two main sections: @itemize @bullet @item A @emph{Workspace area}, initially greyed out, which you will use for creating and editing source files @item Directly below, a @emph{Messages area}, which initially displays a ``Welcome'' message. (If the Messages area is not visible, drag its border upward to expand it.) @end itemize @noindent Select @code{File} on the menu bar, and then the @code{New} command. The Workspace area will become white, and you can now enter the source program explicitly. Type the following text @smallexample @c ada @group with Ada.Text_IO; use Ada.Text_IO; procedure Hello is begin Put_Line("Hello from GPS!"); end Hello; @end group @end smallexample @noindent Select @code{File}, then @code{Save As}, and enter the source file name @file{hello.adb}. The file will be saved in the same directory you specified as the location of the default project file. @item @emph{Updating the project file} You need to add the new source file to the project. To do this, select the @code{Project} menu and then @code{Edit project properties}. Click the @code{Main files} tab on the left, and then the @code{Add} button. Choose @file{hello.adb} from the list, and press @code{Open}. The project settings window will reflect this action. Click @code{OK}. @item @emph{Building and running the program} In the main GPS window, now choose the @code{Build} menu, then @code{Make}, and select @file{hello.adb}. The Messages window will display the resulting invocations of @command{gcc}, @command{gnatbind}, and @command{gnatlink} (reflecting the default switch settings from the project file that you created) and then a ``successful compilation/build'' message. To run the program, choose the @code{Build} menu, then @code{Run}, and select @command{hello}. An @emph{Arguments Selection} window will appear. There are no command line arguments, so just click @code{OK}. The Messages window will now display the program's output (the string @code{Hello from GPS}), and at the bottom of the GPS window a status update is displayed (@code{Run: hello}). Close the GPS window (or select @code{File}, then @code{Exit}) to terminate this GPS session. @end enumerate @node Simple Debugging with GPS @subsection Simple Debugging with GPS @noindent This section illustrates basic debugging techniques (setting breakpoints, examining/modifying variables, single stepping). @enumerate @item @emph{Opening a project} Start GPS and select @code{Open existing project}; browse to specify the project file @file{sample.prj} that you had created in the earlier example. @item @emph{Creating a source file} Select @code{File}, then @code{New}, and type in the following program: @smallexample @c ada @group with Ada.Text_IO; use Ada.Text_IO; procedure Example is Line : String (1..80); N : Natural; begin Put_Line("Type a line of text at each prompt; an empty line to exit"); loop Put(": "); Get_Line (Line, N); Put_Line (Line (1..N) ); exit when N=0; end loop; end Example; @end group @end smallexample @noindent Select @code{File}, then @code{Save as}, and enter the file name @file{example.adb}. @item @emph{Updating the project file} Add @code{Example} as a new main unit for the project: @enumerate a @item Select @code{Project}, then @code{Edit Project Properties}. @item Select the @code{Main files} tab, click @code{Add}, then select the file @file{example.adb} from the list, and click @code{Open}. You will see the file name appear in the list of main units @item Click @code{OK} @end enumerate @item @emph{Building/running the executable} To build the executable select @code{Build}, then @code{Make}, and then choose @file{example.adb}. Run the program to see its effect (in the Messages area). Each line that you enter is displayed; an empty line will cause the loop to exit and the program to terminate. @item @emph{Debugging the program} Note that the @option{-g} switches to @command{gcc} and @command{gnatlink}, which are required for debugging, are on by default when you create a new project. Thus unless you intentionally remove these settings, you will be able to debug any program that you develop using GPS. @enumerate a @item @emph{Initializing} Select @code{Debug}, then @code{Initialize}, then @file{example} @item @emph{Setting a breakpoint} After performing the initialization step, you will observe a small icon to the right of each line number. This serves as a toggle for breakpoints; clicking the icon will set a breakpoint at the corresponding line (the icon will change to a red circle with an ``x''), and clicking it again will remove the breakpoint / reset the icon. For purposes of this example, set a breakpoint at line 10 (the statement @code{Put_Line@ (Line@ (1..N));} @item @emph{Starting program execution} Select @code{Debug}, then @code{Run}. When the @code{Program Arguments} window appears, click @code{OK}. A console window will appear; enter some line of text, e.g.@: @code{abcde}, at the prompt. The program will pause execution when it gets to the breakpoint, and the corresponding line is highlighted. @item @emph{Examining a variable} Move the mouse over one of the occurrences of the variable @code{N}. You will see the value (5) displayed, in ``tool tip'' fashion. Right click on @code{N}, select @code{Debug}, then select @code{Display N}. You will see information about @code{N} appear in the @code{Debugger Data} pane, showing the value as 5. @item @emph{Assigning a new value to a variable} Right click on the @code{N} in the @code{Debugger Data} pane, and select @code{Set value of N}. When the input window appears, enter the value @code{4} and click @code{OK}. This value does not automatically appear in the @code{Debugger Data} pane; to see it, right click again on the @code{N} in the @code{Debugger Data} pane and select @code{Update value}. The new value, 4, will appear in red. @item @emph{Single stepping} Select @code{Debug}, then @code{Next}. This will cause the next statement to be executed, in this case the call of @code{Put_Line} with the string slice. Notice in the console window that the displayed string is simply @code{abcd} and not @code{abcde} which you had entered. This is because the upper bound of the slice is now 4 rather than 5. @item @emph{Removing a breakpoint} Toggle the breakpoint icon at line 10. @item @emph{Resuming execution from a breakpoint} Select @code{Debug}, then @code{Continue}. The program will reach the next iteration of the loop, and wait for input after displaying the prompt. This time, just hit the @kbd{Enter} key. The value of @code{N} will be 0, and the program will terminate. The console window will disappear. @end enumerate @end enumerate @end ifclear @node The GNAT Compilation Model @chapter The GNAT Compilation Model @cindex GNAT compilation model @cindex Compilation model @menu * Source Representation:: * Foreign Language Representation:: * File Naming Rules:: * Using Other File Names:: * Alternative File Naming Schemes:: * Generating Object Files:: * Source Dependencies:: * The Ada Library Information Files:: * Binding an Ada Program:: * Mixed Language Programming:: @ifclear vms * Building Mixed Ada & C++ Programs:: * Comparison between GNAT and C/C++ Compilation Models:: @end ifclear * Comparison between GNAT and Conventional Ada Library Models:: @ifset vms * Placement of temporary files:: @end ifset @end menu @noindent This chapter describes the compilation model used by GNAT. Although similar to that used by other languages, such as C and C++, this model is substantially different from the traditional Ada compilation models, which are based on a library. The model is initially described without reference to the library-based model. If you have not previously used an Ada compiler, you need only read the first part of this chapter. The last section describes and discusses the differences between the GNAT model and the traditional Ada compiler models. If you have used other Ada compilers, this section will help you to understand those differences, and the advantages of the GNAT model. @node Source Representation @section Source Representation @cindex Latin-1 @noindent Ada source programs are represented in standard text files, using Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar 7-bit ASCII set, plus additional characters used for representing foreign languages (@pxref{Foreign Language Representation} for support of non-USA character sets). The format effector characters are represented using their standard ASCII encodings, as follows: @table @code @item VT @findex VT Vertical tab, @code{16#0B#} @item HT @findex HT Horizontal tab, @code{16#09#} @item CR @findex CR Carriage return, @code{16#0D#} @item LF @findex LF Line feed, @code{16#0A#} @item FF @findex FF Form feed, @code{16#0C#} @end table @noindent Source files are in standard text file format. In addition, GNAT will recognize a wide variety of stream formats, in which the end of physical lines is marked by any of the following sequences: @code{LF}, @code{CR}, @code{CR-LF}, or @code{LF-CR}. This is useful in accommodating files that are imported from other operating systems. @cindex End of source file @cindex Source file, end @findex SUB The end of a source file is normally represented by the physical end of file. However, the control character @code{16#1A#} (@code{SUB}) is also recognized as signalling the end of the source file. Again, this is provided for compatibility with other operating systems where this code is used to represent the end of file. Each file contains a single Ada compilation unit, including any pragmas associated with the unit. For example, this means you must place a package declaration (a package @dfn{spec}) and the corresponding body in separate files. An Ada @dfn{compilation} (which is a sequence of compilation units) is represented using a sequence of files. Similarly, you will place each subunit or child unit in a separate file. @node Foreign Language Representation @section Foreign Language Representation @noindent GNAT supports the standard character sets defined in Ada as well as several other non-standard character sets for use in localized versions of the compiler (@pxref{Character Set Control}). @menu * Latin-1:: * Other 8-Bit Codes:: * Wide Character Encodings:: @end menu @node Latin-1 @subsection Latin-1 @cindex Latin-1 @noindent The basic character set is Latin-1. This character set is defined by ISO standard 8859, part 1. The lower half (character codes @code{16#00#} @dots{} @code{16#7F#)} is identical to standard ASCII coding, but the upper half is used to represent additional characters. These include extended letters used by European languages, such as French accents, the vowels with umlauts used in German, and the extra letter A-ring used in Swedish. @findex Ada.Characters.Latin_1 For a complete list of Latin-1 codes and their encodings, see the source file of library unit @code{Ada.Characters.Latin_1} in file @file{a-chlat1.ads}. You may use any of these extended characters freely in character or string literals. In addition, the extended characters that represent letters can be used in identifiers. @node Other 8-Bit Codes @subsection Other 8-Bit Codes @noindent GNAT also supports several other 8-bit coding schemes: @table @asis @item ISO 8859-2 (Latin-2) @cindex Latin-2 @cindex ISO 8859-2 Latin-2 letters allowed in identifiers, with uppercase and lowercase equivalence. @item ISO 8859-3 (Latin-3) @cindex Latin-3 @cindex ISO 8859-3 Latin-3 letters allowed in identifiers, with uppercase and lowercase equivalence. @item ISO 8859-4 (Latin-4) @cindex Latin-4 @cindex ISO 8859-4 Latin-4 letters allowed in identifiers, with uppercase and lowercase equivalence. @item ISO 8859-5 (Cyrillic) @cindex ISO 8859-5 @cindex Cyrillic ISO 8859-5 letters (Cyrillic) allowed in identifiers, with uppercase and lowercase equivalence. @item ISO 8859-15 (Latin-9) @cindex ISO 8859-15 @cindex Latin-9 ISO 8859-15 (Latin-9) letters allowed in identifiers, with uppercase and lowercase equivalence @item IBM PC (code page 437) @cindex code page 437 This code page is the normal default for PCs in the U.S. It corresponds to the original IBM PC character set. This set has some, but not all, of the extended Latin-1 letters, but these letters do not have the same encoding as Latin-1. In this mode, these letters are allowed in identifiers with uppercase and lowercase equivalence. @item IBM PC (code page 850) @cindex code page 850 This code page is a modification of 437 extended to include all the Latin-1 letters, but still not with the usual Latin-1 encoding. In this mode, all these letters are allowed in identifiers with uppercase and lowercase equivalence. @item Full Upper 8-bit Any character in the range 80-FF allowed in identifiers, and all are considered distinct. In other words, there are no uppercase and lowercase equivalences in this range. This is useful in conjunction with certain encoding schemes used for some foreign character sets (e.g., the typical method of representing Chinese characters on the PC). @item No Upper-Half No upper-half characters in the range 80-FF are allowed in identifiers. This gives Ada 83 compatibility for identifier names. @end table @noindent For precise data on the encodings permitted, and the uppercase and lowercase equivalences that are recognized, see the file @file{csets.adb} in the GNAT compiler sources. You will need to obtain a full source release of GNAT to obtain this file. @node Wide Character Encodings @subsection Wide Character Encodings @noindent GNAT allows wide character codes to appear in character and string literals, and also optionally in identifiers, by means of the following possible encoding schemes: @table @asis @item Hex Coding In this encoding, a wide character is represented by the following five character sequence: @smallexample ESC a b c d @end smallexample @noindent Where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal characters (using uppercase letters) of the wide character code. For example, ESC A345 is used to represent the wide character with code @code{16#A345#}. This scheme is compatible with use of the full Wide_Character set. @item Upper-Half Coding @cindex Upper-Half Coding The wide character with encoding @code{16#abcd#} where the upper bit is on (in other words, ``a'' is in the range 8-F) is represented as two bytes, @code{16#ab#} and @code{16#cd#}. The second byte cannot be a format control character, but is not required to be in the upper half. This method can be also used for shift-JIS or EUC, where the internal coding matches the external coding. @item Shift JIS Coding @cindex Shift JIS Coding A wide character is represented by a two-character sequence, @code{16#ab#} and @code{16#cd#}, with the restrictions described for upper-half encoding as described above. The internal character code is the corresponding JIS character according to the standard algorithm for Shift-JIS conversion. Only characters defined in the JIS code set table can be used with this encoding method. @item EUC Coding @cindex EUC Coding A wide character is represented by a two-character sequence @code{16#ab#} and @code{16#cd#}, with both characters being in the upper half. The internal character code is the corresponding JIS character according to the EUC encoding algorithm. Only characters defined in the JIS code set table can be used with this encoding method. @item UTF-8 Coding A wide character is represented using UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO 10646-1/Am.2. Depending on the character value, the representation is a one, two, or three byte sequence: @smallexample @iftex @leftskip=.7cm @end iftex 16#0000#-16#007f#: 2#0@var{xxxxxxx}# 16#0080#-16#07ff#: 2#110@var{xxxxx}# 2#10@var{xxxxxx}# 16#0800#-16#ffff#: 2#1110@var{xxxx}# 2#10@var{xxxxxx}# 2#10@var{xxxxxx}# @end smallexample @noindent where the @var{xxx} bits correspond to the left-padded bits of the 16-bit character value. Note that all lower half ASCII characters are represented as ASCII bytes and all upper half characters and other wide characters are represented as sequences of upper-half (The full UTF-8 scheme allows for encoding 31-bit characters as 6-byte sequences, but in this implementation, all UTF-8 sequences of four or more bytes length will be treated as illegal). @item Brackets Coding In this encoding, a wide character is represented by the following eight character sequence: @smallexample [ " a b c d " ] @end smallexample @noindent Where @code{a}, @code{b}, @code{c}, @code{d} are the four hexadecimal characters (using uppercase letters) of the wide character code. For example, [``A345''] is used to represent the wide character with code @code{16#A345#}. It is also possible (though not required) to use the Brackets coding for upper half characters. For example, the code @code{16#A3#} can be represented as @code{[``A3'']}. This scheme is compatible with use of the full Wide_Character set, and is also the method used for wide character encoding in the standard ACVC (Ada Compiler Validation Capability) test suite distributions. @end table @noindent Note: Some of these coding schemes do not permit the full use of the Ada character set. For example, neither Shift JIS, nor EUC allow the use of the upper half of the Latin-1 set. @node File Naming Rules @section File Naming Rules @noindent The default file name is determined by the name of the unit that the file contains. The name is formed by taking the full expanded name of the unit and replacing the separating dots with hyphens and using ^lowercase^uppercase^ for all letters. An exception arises if the file name generated by the above rules starts with one of the characters @ifset vms @samp{A}, @samp{G}, @samp{I}, or @samp{S}, @end ifset @ifclear vms @samp{a}, @samp{g}, @samp{i}, or @samp{s}, @end ifclear and the second character is a minus. In this case, the character ^tilde^dollar sign^ is used in place of the minus. The reason for this special rule is to avoid clashes with the standard names for child units of the packages System, Ada, Interfaces, and GNAT, which use the prefixes @ifset vms @samp{S-}, @samp{A-}, @samp{I-}, and @samp{G-}, @end ifset @ifclear vms @samp{s-}, @samp{a-}, @samp{i-}, and @samp{g-}, @end ifclear respectively. The file extension is @file{.ads} for a spec and @file{.adb} for a body. The following list shows some examples of these rules. @table @file @item main.ads Main (spec) @item main.adb Main (body) @item arith_functions.ads Arith_Functions (package spec) @item arith_functions.adb Arith_Functions (package body) @item func-spec.ads Func.Spec (child package spec) @item func-spec.adb Func.Spec (child package body) @item main-sub.adb Sub (subunit of Main) @item ^a~bad.adb^A$BAD.ADB^ A.Bad (child package body) @end table @noindent Following these rules can result in excessively long file names if corresponding unit names are long (for example, if child units or subunits are heavily nested). An option is available to shorten such long file names (called file name ``krunching''). This may be particularly useful when programs being developed with GNAT are to be used on operating systems with limited file name lengths. @xref{Using gnatkr}. Of course, no file shortening algorithm can guarantee uniqueness over all possible unit names; if file name krunching is used, it is your responsibility to ensure no name clashes occur. Alternatively you can specify the exact file names that you want used, as described in the next section. Finally, if your Ada programs are migrating from a compiler with a different naming convention, you can use the gnatchop utility to produce source files that follow the GNAT naming conventions. (For details @pxref{Renaming Files Using gnatchop}.) Note: in the case of @code{Windows NT/XP} or @code{OpenVMS} operating systems, case is not significant. So for example on @code{Windows XP} if the canonical name is @code{main-sub.adb}, you can use the file name @code{Main-Sub.adb} instead. However, case is significant for other operating systems, so for example, if you want to use other than canonically cased file names on a Unix system, you need to follow the procedures described in the next section. @node Using Other File Names @section Using Other File Names @cindex File names @noindent In the previous section, we have described the default rules used by GNAT to determine the file name in which a given unit resides. It is often convenient to follow these default rules, and if you follow them, the compiler knows without being explicitly told where to find all the files it needs. However, in some cases, particularly when a program is imported from another Ada compiler environment, it may be more convenient for the programmer to specify which file names contain which units. GNAT allows arbitrary file names to be used by means of the Source_File_Name pragma. The form of this pragma is as shown in the following examples: @cindex Source_File_Name pragma @smallexample @c ada @cartouche pragma Source_File_Name (My_Utilities.Stacks, Spec_File_Name => "myutilst_a.ada"); pragma Source_File_name (My_Utilities.Stacks, Body_File_Name => "myutilst.ada"); @end cartouche @end smallexample @noindent As shown in this example, the first argument for the pragma is the unit name (in this example a child unit). The second argument has the form of a named association. The identifier indicates whether the file name is for a spec or a body; the file name itself is given by a string literal. The source file name pragma is a configuration pragma, which means that normally it will be placed in the @file{gnat.adc} file used to hold configuration pragmas that apply to a complete compilation environment. For more details on how the @file{gnat.adc} file is created and used see @ref{Handling of Configuration Pragmas}. @cindex @file{gnat.adc} @ifclear vms GNAT allows completely arbitrary file names to be specified using the source file name pragma. However, if the file name specified has an extension other than @file{.ads} or @file{.adb} it is necessary to use a special syntax when compiling the file. The name in this case must be preceded by the special sequence @option{-x} followed by a space and the name of the language, here @code{ada}, as in: @smallexample $ gcc -c -x ada peculiar_file_name.sim @end smallexample @end ifclear @noindent @command{gnatmake} handles non-standard file names in the usual manner (the non-standard file name for the main program is simply used as the argument to gnatmake). Note that if the extension is also non-standard, then it must be included in the @command{gnatmake} command, it may not be omitted. @node Alternative File Naming Schemes @section Alternative File Naming Schemes @cindex File naming schemes, alternative @cindex File names In the previous section, we described the use of the @code{Source_File_Name} pragma to allow arbitrary names to be assigned to individual source files. However, this approach requires one pragma for each file, and especially in large systems can result in very long @file{gnat.adc} files, and also create a maintenance problem. GNAT also provides a facility for specifying systematic file naming schemes other than the standard default naming scheme previously described. An alternative scheme for naming is specified by the use of @code{Source_File_Name} pragmas having the following format: @cindex Source_File_Name pragma @smallexample @c ada pragma Source_File_Name ( Spec_File_Name => FILE_NAME_PATTERN @r{[},Casing => CASING_SPEC@r{]} @r{[},Dot_Replacement => STRING_LITERAL@r{]}); pragma Source_File_Name ( Body_File_Name => FILE_NAME_PATTERN @r{[},Casing => CASING_SPEC@r{]} @r{[},Dot_Replacement => STRING_LITERAL@r{]}); pragma Source_File_Name ( Subunit_File_Name => FILE_NAME_PATTERN @r{[},Casing => CASING_SPEC@r{]} @r{[},Dot_Replacement => STRING_LITERAL@r{]}); FILE_NAME_PATTERN ::= STRING_LITERAL CASING_SPEC ::= Lowercase | Uppercase | Mixedcase @end smallexample @noindent The @code{FILE_NAME_PATTERN} string shows how the file name is constructed. It contains a single asterisk character, and the unit name is substituted systematically for this asterisk. The optional parameter @code{Casing} indicates whether the unit name is to be all upper-case letters, all lower-case letters, or mixed-case. If no @code{Casing} parameter is used, then the default is all ^lower-case^upper-case^. The optional @code{Dot_Replacement} string is used to replace any periods that occur in subunit or child unit names. If no @code{Dot_Replacement} argument is used then separating dots appear unchanged in the resulting file name. Although the above syntax indicates that the @code{Casing} argument must appear before the @code{Dot_Replacement} argument, but it is also permissible to write these arguments in the opposite order. As indicated, it is possible to specify different naming schemes for bodies, specs, and subunits. Quite often the rule for subunits is the same as the rule for bodies, in which case, there is no need to give a separate @code{Subunit_File_Name} rule, and in this case the @code{Body_File_name} rule is used for subunits as well. The separate rule for subunits can also be used to implement the rather unusual case of a compilation environment (e.g.@: a single directory) which contains a subunit and a child unit with the same unit name. Although both units cannot appear in the same partition, the Ada Reference Manual allows (but does not require) the possibility of the two units coexisting in the same environment. The file name translation works in the following steps: @itemize @bullet @item If there is a specific @code{Source_File_Name} pragma for the given unit, then this is always used, and any general pattern rules are ignored. @item If there is a pattern type @code{Source_File_Name} pragma that applies to the unit, then the resulting file name will be used if the file exists. If more than one pattern matches, the latest one will be tried first, and the first attempt resulting in a reference to a file that exists will be used. @item If no pattern type @code{Source_File_Name} pragma that applies to the unit for which the corresponding file exists, then the standard GNAT default naming rules are used. @end itemize @noindent As an example of the use of this mechanism, consider a commonly used scheme in which file names are all lower case, with separating periods copied unchanged to the resulting file name, and specs end with @file{.1.ada}, and bodies end with @file{.2.ada}. GNAT will follow this scheme if the following two pragmas appear: @smallexample @c ada pragma Source_File_Name (Spec_File_Name => "*.1.ada"); pragma Source_File_Name (Body_File_Name => "*.2.ada"); @end smallexample @noindent The default GNAT scheme is actually implemented by providing the following default pragmas internally: @smallexample @c ada pragma Source_File_Name (Spec_File_Name => "*.ads", Dot_Replacement => "-"); pragma Source_File_Name (Body_File_Name => "*.adb", Dot_Replacement => "-"); @end smallexample @noindent Our final example implements a scheme typically used with one of the Ada 83 compilers, where the separator character for subunits was ``__'' (two underscores), specs were identified by adding @file{_.ADA}, bodies by adding @file{.ADA}, and subunits by adding @file{.SEP}. All file names were upper case. Child units were not present of course since this was an Ada 83 compiler, but it seems reasonable to extend this scheme to use the same double underscore separator for child units. @smallexample @c ada pragma Source_File_Name (Spec_File_Name => "*_.ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Body_File_Name => "*.ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Subunit_File_Name => "*.SEP", Dot_Replacement => "__", Casing = Uppercase); @end smallexample @node Generating Object Files @section Generating Object Files @noindent An Ada program consists of a set of source files, and the first step in compiling the program is to generate the corresponding object files. These are generated by compiling a subset of these source files. The files you need to compile are the following: @itemize @bullet @item If a package spec has no body, compile the package spec to produce the object file for the package. @item If a package has both a spec and a body, compile the body to produce the object file for the package. The source file for the package spec need not be compiled in this case because there is only one object file, which contains the code for both the spec and body of the package. @item For a subprogram, compile the subprogram body to produce the object file for the subprogram. The spec, if one is present, is as usual in a separate file, and need not be compiled. @item @cindex Subunits In the case of subunits, only compile the parent unit. A single object file is generated for the entire subunit tree, which includes all the subunits. @item Compile child units independently of their parent units (though, of course, the spec of all the ancestor unit must be present in order to compile a child unit). @item @cindex Generics Compile generic units in the same manner as any other units. The object files in this case are small dummy files that contain at most the flag used for elaboration checking. This is because GNAT always handles generic instantiation by means of macro expansion. However, it is still necessary to compile generic units, for dependency checking and elaboration purposes. @end itemize @noindent The preceding rules describe the set of files that must be compiled to generate the object files for a program. Each object file has the same name as the corresponding source file, except that the extension is @file{.o} as usual. You may wish to compile other files for the purpose of checking their syntactic and semantic correctness. For example, in the case where a package has a separate spec and body, you would not normally compile the spec. However, it is convenient in practice to compile the spec to make sure it is error-free before compiling clients of this spec, because such compilations will fail if there is an error in the spec. GNAT provides an option for compiling such files purely for the purposes of checking correctness; such compilations are not required as part of the process of building a program. To compile a file in this checking mode, use the @option{-gnatc} switch. @node Source Dependencies @section Source Dependencies @noindent A given object file clearly depends on the source file which is compiled to produce it. Here we are using @dfn{depends} in the sense of a typical @code{make} utility; in other words, an object file depends on a source file if changes to the source file require the object file to be recompiled. In addition to this basic dependency, a given object may depend on additional source files as follows: @itemize @bullet @item If a file being compiled @code{with}'s a unit @var{X}, the object file depends on the file containing the spec of unit @var{X}. This includes files that are @code{with}'ed implicitly either because they are parents of @code{with}'ed child units or they are run-time units required by the language constructs used in a particular unit. @item If a file being compiled instantiates a library level generic unit, the object file depends on both the spec and body files for this generic unit. @item If a file being compiled instantiates a generic unit defined within a package, the object file depends on the body file for the package as well as the spec file. @item @findex Inline @cindex @option{-gnatn} switch If a file being compiled contains a call to a subprogram for which pragma @code{Inline} applies and inlining is activated with the @option{-gnatn} switch, the object file depends on the file containing the body of this subprogram as well as on the file containing the spec. Note that for inlining to actually occur as a result of the use of this switch, it is necessary to compile in optimizing mode. @cindex @option{-gnatN} switch The use of @option{-gnatN} activates inlining optimization that is performed by the front end of the compiler. This inlining does not require that the code generation be optimized. Like @option{-gnatn}, the use of this switch generates additional dependencies. When using a gcc-based back end (in practice this means using any version of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of @option{-gnatN} is deprecated, and the use of @option{-gnatn} is preferred. Historically front end inlining was more extensive than the gcc back end inlining, but that is no longer the case. @item If an object file @file{O} depends on the proper body of a subunit through inlining or instantiation, it depends on the parent unit of the subunit. This means that any modification of the parent unit or one of its subunits affects the compilation of @file{O}. @item The object file for a parent unit depends on all its subunit body files. @item The previous two rules meant that for purposes of computing dependencies and recompilation, a body and all its subunits are treated as an indivisible whole. @noindent These rules are applied transitively: if unit @code{A} @code{with}'s unit @code{B}, whose elaboration calls an inlined procedure in package @code{C}, the object file for unit @code{A} will depend on the body of @code{C}, in file @file{c.adb}. The set of dependent files described by these rules includes all the files on which the unit is semantically dependent, as dictated by the Ada language standard. However, it is a superset of what the standard describes, because it includes generic, inline, and subunit dependencies. An object file must be recreated by recompiling the corresponding source file if any of the source files on which it depends are modified. For example, if the @code{make} utility is used to control compilation, the rule for an Ada object file must mention all the source files on which the object file depends, according to the above definition. The determination of the necessary recompilations is done automatically when one uses @command{gnatmake}. @end itemize @node The Ada Library Information Files @section The Ada Library Information Files @cindex Ada Library Information files @cindex @file{ALI} files @noindent Each compilation actually generates two output files. The first of these is the normal object file that has a @file{.o} extension. The second is a text file containing full dependency information. It has the same name as the source file, but an @file{.ali} extension. This file is known as the Ada Library Information (@file{ALI}) file. The following information is contained in the @file{ALI} file. @itemize @bullet @item Version information (indicates which version of GNAT was used to compile the unit(s) in question) @item Main program information (including priority and time slice settings, as well as the wide character encoding used during compilation). @item List of arguments used in the @command{gcc} command for the compilation @item Attributes of the unit, including configuration pragmas used, an indication of whether the compilation was successful, exception model used etc. @item A list of relevant restrictions applying to the unit (used for consistency) checking. @item Categorization information (e.g.@: use of pragma @code{Pure}). @item Information on all @code{with}'ed units, including presence of @code{Elaborate} or @code{Elaborate_All} pragmas. @item Information from any @code{Linker_Options} pragmas used in the unit @item Information on the use of @code{Body_Version} or @code{Version} attributes in the unit. @item Dependency information. This is a list of files, together with time stamp and checksum information. These are files on which the unit depends in the sense that recompilation is required if any of these units are modified. @item Cross-reference data. Contains information on all entities referenced in the unit. Used by tools like @code{gnatxref} and @code{gnatfind} to provide cross-reference information. @end itemize @noindent For a full detailed description of the format of the @file{ALI} file, see the source of the body of unit @code{Lib.Writ}, contained in file @file{lib-writ.adb} in the GNAT compiler sources. @node Binding an Ada Program @section Binding an Ada Program @noindent When using languages such as C and C++, once the source files have been compiled the only remaining step in building an executable program is linking the object modules together. This means that it is possible to link an inconsistent version of a program, in which two units have included different versions of the same header. The rules of Ada do not permit such an inconsistent program to be built. For example, if two clients have different versions of the same package, it is illegal to build a program containing these two clients. These rules are enforced by the GNAT binder, which also determines an elaboration order consistent with the Ada rules. The GNAT binder is run after all the object files for a program have been created. It is given the name of the main program unit, and from this it determines the set of units required by the program, by reading the corresponding ALI files. It generates error messages if the program is inconsistent or if no valid order of elaboration exists. If no errors are detected, the binder produces a main program, in Ada by default, that contains calls to the elaboration procedures of those compilation unit that require them, followed by a call to the main program. This Ada program is compiled to generate the object file for the main program. The name of the Ada file is @file{b~@var{xxx}.adb} (with the corresponding spec @file{b~@var{xxx}.ads}) where @var{xxx} is the name of the main program unit. Finally, the linker is used to build the resulting executable program, using the object from the main program from the bind step as well as the object files for the Ada units of the program. @node Mixed Language Programming @section Mixed Language Programming @cindex Mixed Language Programming @noindent This section describes how to develop a mixed-language program, specifically one that comprises units in both Ada and C. @menu * Interfacing to C:: * Calling Conventions:: @end menu @node Interfacing to C @subsection Interfacing to C @noindent Interfacing Ada with a foreign language such as C involves using compiler directives to import and/or export entity definitions in each language---using @code{extern} statements in C, for instance, and the @code{Import}, @code{Export}, and @code{Convention} pragmas in Ada. A full treatment of these topics is provided in Appendix B, section 1 of the Ada Reference Manual. There are two ways to build a program using GNAT that contains some Ada sources and some foreign language sources, depending on whether or not the main subprogram is written in Ada. Here is a source example with the main subprogram in Ada: @smallexample /* file1.c */ #include void print_num (int num) @{ printf ("num is %d.\n", num); return; @} /* file2.c */ /* num_from_Ada is declared in my_main.adb */ extern int num_from_Ada; int get_num (void) @{ return num_from_Ada; @} @end smallexample @smallexample @c ada -- my_main.adb procedure My_Main is -- Declare then export an Integer entity called num_from_Ada My_Num : Integer := 10; pragma Export (C, My_Num, "num_from_Ada"); -- Declare an Ada function spec for Get_Num, then use -- C function get_num for the implementation. function Get_Num return Integer; pragma Import (C, Get_Num, "get_num"); -- Declare an Ada procedure spec for Print_Num, then use -- C function print_num for the implementation. procedure Print_Num (Num : Integer); pragma Import (C, Print_Num, "print_num"); begin Print_Num (Get_Num); end My_Main; @end smallexample @enumerate @item To build this example, first compile the foreign language files to generate object files: @smallexample ^gcc -c file1.c^gcc -c FILE1.C^ ^gcc -c file2.c^gcc -c FILE2.C^ @end smallexample @item Then, compile the Ada units to produce a set of object files and ALI files: @smallexample gnatmake ^-c^/ACTIONS=COMPILE^ my_main.adb @end smallexample @item Run the Ada binder on the Ada main program: @smallexample gnatbind my_main.ali @end smallexample @item Link the Ada main program, the Ada objects and the other language objects: @smallexample gnatlink my_main.ali file1.o file2.o @end smallexample @end enumerate The last three steps can be grouped in a single command: @smallexample gnatmake my_main.adb -largs file1.o file2.o @end smallexample @cindex Binder output file @noindent If the main program is in a language other than Ada, then you may have more than one entry point into the Ada subsystem. You must use a special binder option to generate callable routines that initialize and finalize the Ada units (@pxref{Binding with Non-Ada Main Programs}). Calls to the initialization and finalization routines must be inserted in the main program, or some other appropriate point in the code. The call to initialize the Ada units must occur before the first Ada subprogram is called, and the call to finalize the Ada units must occur after the last Ada subprogram returns. The binder will place the initialization and finalization subprograms into the @file{b~@var{xxx}.adb} file where they can be accessed by your C sources. To illustrate, we have the following example: @smallexample /* main.c */ extern void adainit (void); extern void adafinal (void); extern int add (int, int); extern int sub (int, int); int main (int argc, char *argv[]) @{ int a = 21, b = 7; adainit(); /* Should print "21 + 7 = 28" */ printf ("%d + %d = %d\n", a, b, add (a, b)); /* Should print "21 - 7 = 14" */ printf ("%d - %d = %d\n", a, b, sub (a, b)); adafinal(); @} @end smallexample @smallexample @c ada -- unit1.ads package Unit1 is function Add (A, B : Integer) return Integer; pragma Export (C, Add, "add"); end Unit1; -- unit1.adb package body Unit1 is function Add (A, B : Integer) return Integer is begin return A + B; end Add; end Unit1; -- unit2.ads package Unit2 is function Sub (A, B : Integer) return Integer; pragma Export (C, Sub, "sub"); end Unit2; -- unit2.adb package body Unit2 is function Sub (A, B : Integer) return Integer is begin return A - B; end Sub; end Unit2; @end smallexample @enumerate @item The build procedure for this application is similar to the last example's. First, compile the foreign language files to generate object files: @smallexample ^gcc -c main.c^gcc -c main.c^ @end smallexample @item Next, compile the Ada units to produce a set of object files and ALI files: @smallexample gnatmake ^-c^/ACTIONS=COMPILE^ unit1.adb gnatmake ^-c^/ACTIONS=COMPILE^ unit2.adb @end smallexample @item Run the Ada binder on every generated ALI file. Make sure to use the @option{-n} option to specify a foreign main program: @smallexample gnatbind ^-n^/NOMAIN^ unit1.ali unit2.ali @end smallexample @item Link the Ada main program, the Ada objects and the foreign language objects. You need only list the last ALI file here: @smallexample gnatlink unit2.ali main.o -o exec_file @end smallexample This procedure yields a binary executable called @file{exec_file}. @end enumerate @noindent Depending on the circumstances (for example when your non-Ada main object does not provide symbol @code{main}), you may also need to instruct the GNAT linker not to include the standard startup objects by passing the @option{^-nostartfiles^/NOSTART_FILES^} switch to @command{gnatlink}. @node Calling Conventions @subsection Calling Conventions @cindex Foreign Languages @cindex Calling Conventions GNAT follows standard calling sequence conventions and will thus interface to any other language that also follows these conventions. The following Convention identifiers are recognized by GNAT: @table @code @cindex Interfacing to Ada @cindex Other Ada compilers @cindex Convention Ada @item Ada This indicates that the standard Ada calling sequence will be used and all Ada data items may be passed without any limitations in the case where GNAT is used to generate both the caller and callee. It is also possible to mix GNAT generated code and code generated by another Ada compiler. In this case, the data types should be restricted to simple cases, including primitive types. Whether complex data types can be passed depends on the situation. Probably it is safe to pass simple arrays, such as arrays of integers or floats. Records may or may not work, depending on whether both compilers lay them out identically. Complex structures involving variant records, access parameters, tasks, or protected types, are unlikely to be able to be passed. Note that in the case of GNAT running on a platform that supports HP Ada 83, a higher degree of compatibility can be guaranteed, and in particular records are layed out in an identical manner in the two compilers. Note also that if output from two different compilers is mixed, the program is responsible for dealing with elaboration issues. Probably the safest approach is to write the main program in the version of Ada other than GNAT, so that it takes care of its own elaboration requirements, and then call the GNAT-generated adainit procedure to ensure elaboration of the GNAT components. Consult the documentation of the other Ada compiler for further details on elaboration. However, it is not possible to mix the tasking run time of GNAT and HP Ada 83, All the tasking operations must either be entirely within GNAT compiled sections of the program, or entirely within HP Ada 83 compiled sections of the program. @cindex Interfacing to Assembly @cindex Convention Assembler @item Assembler Specifies assembler as the convention. In practice this has the same effect as convention Ada (but is not equivalent in the sense of being considered the same convention). @cindex Convention Asm @findex Asm @item Asm Equivalent to Assembler. @cindex Interfacing to COBOL @cindex Convention COBOL @findex COBOL @item COBOL Data will be passed according to the conventions described in section B.4 of the Ada Reference Manual. @findex C @cindex Interfacing to C @cindex Convention C @item C Data will be passed according to the conventions described in section B.3 of the Ada Reference Manual. A note on interfacing to a C ``varargs'' function: @findex C varargs function @cindex Interfacing to C varargs function @cindex varargs function interfaces @itemize @bullet @item In C, @code{varargs} allows a function to take a variable number of arguments. There is no direct equivalent in this to Ada. One approach that can be used is to create a C wrapper for each different profile and then interface to this C wrapper. For example, to print an @code{int} value using @code{printf}, create a C function @code{printfi} that takes two arguments, a pointer to a string and an int, and calls @code{printf}. Then in the Ada program, use pragma @code{Import} to interface to @code{printfi}. @item It may work on some platforms to directly interface to a @code{varargs} function by providing a specific Ada profile for a particular call. However, this does not work on all platforms, since there is no guarantee that the calling sequence for a two argument normal C function is the same as for calling a @code{varargs} C function with the same two arguments. @end itemize @cindex Convention Default @findex Default @item Default Equivalent to C. @cindex Convention External @findex External @item External Equivalent to C. @ifclear vms @findex C++ @cindex Interfacing to C++ @cindex Convention C++ @item C_Plus_Plus (or CPP) This stands for C++. For most purposes this is identical to C. See the separate description of the specialized GNAT pragmas relating to C++ interfacing for further details. @end ifclear @findex Fortran @cindex Interfacing to Fortran @cindex Convention Fortran @item Fortran Data will be passed according to the conventions described in section B.5 of the Ada Reference Manual. @item Intrinsic This applies to an intrinsic operation, as defined in the Ada Reference Manual. If a pragma Import (Intrinsic) applies to a subprogram, this means that the body of the subprogram is provided by the compiler itself, usually by means of an efficient code sequence, and that the user does not supply an explicit body for it. In an application program, the pragma may be applied to the following sets of names: @itemize @bullet @item Rotate_Left, Rotate_Right, Shift_Left, Shift_Right, Shift_Right_Arithmetic. The corresponding subprogram declaration must have two formal parameters. The first one must be a signed integer type or a modular type with a binary modulus, and the second parameter must be of type Natural. The return type must be the same as the type of the first argument. The size of this type can only be 8, 16, 32, or 64. @item Binary arithmetic operators: ``+'', ``-'', ``*'', ``/'' The corresponding operator declaration must have parameters and result type that have the same root numeric type (for example, all three are long_float types). This simplifies the definition of operations that use type checking to perform dimensional checks: @smallexample @c ada type Distance is new Long_Float; type Time is new Long_Float; type Velocity is new Long_Float; function "/" (D : Distance; T : Time) return Velocity; pragma Import (Intrinsic, "/"); @end smallexample @noindent This common idiom is often programmed with a generic definition and an explicit body. The pragma makes it simpler to introduce such declarations. It incurs no overhead in compilation time or code size, because it is implemented as a single machine instruction. @item General subprogram entities, to bind an Ada subprogram declaration to a compiler builtin by name with back-ends where such interfaces are available. A typical example is the set of ``__builtin'' functions exposed by the GCC back-end, as in the following example: @smallexample @c ada function builtin_sqrt (F : Float) return Float; pragma Import (Intrinsic, builtin_sqrt, "__builtin_sqrtf"); @end smallexample Most of the GCC builtins are accessible this way, and as for other import conventions (e.g. C), it is the user's responsibility to ensure that the Ada subprogram profile matches the underlying builtin expectations. @end itemize @noindent @ifset unw @findex Stdcall @cindex Convention Stdcall @item Stdcall This is relevant only to Windows XP/2000/NT implementations of GNAT, and specifies that the @code{Stdcall} calling sequence will be used, as defined by the NT API. Nevertheless, to ease building cross-platform bindings this convention will be handled as a @code{C} calling convention on non-Windows platforms. @findex DLL @cindex Convention DLL @item DLL This is equivalent to @code{Stdcall}. @findex Win32 @cindex Convention Win32 @item Win32 This is equivalent to @code{Stdcall}. @end ifset @findex Stubbed @cindex Convention Stubbed @item Stubbed This is a special convention that indicates that the compiler should provide a stub body that raises @code{Program_Error}. @end table @noindent GNAT additionally provides a useful pragma @code{Convention_Identifier} that can be used to parameterize conventions and allow additional synonyms to be specified. For example if you have legacy code in which the convention identifier Fortran77 was used for Fortran, you can use the configuration pragma: @smallexample @c ada pragma Convention_Identifier (Fortran77, Fortran); @end smallexample @noindent And from now on the identifier Fortran77 may be used as a convention identifier (for example in an @code{Import} pragma) with the same meaning as Fortran. @ifclear vms @node Building Mixed Ada & C++ Programs @section Building Mixed Ada and C++ Programs @noindent A programmer inexperienced with mixed-language development may find that building an application containing both Ada and C++ code can be a challenge. This section gives a few hints that should make this task easier. The first section addresses the differences between interfacing with C and interfacing with C++. The second section looks into the delicate problem of linking the complete application from its Ada and C++ parts. The last section gives some hints on how the GNAT run-time library can be adapted in order to allow inter-language dispatching with a new C++ compiler. @menu * Interfacing to C++:: * Linking a Mixed C++ & Ada Program:: * A Simple Example:: * Interfacing with C++ constructors:: * Interfacing with C++ at the Class Level:: @end menu @node Interfacing to C++ @subsection Interfacing to C++ @noindent GNAT supports interfacing with the G++ compiler (or any C++ compiler generating code that is compatible with the G++ Application Binary Interface ---see http://www.codesourcery.com/archives/cxx-abi). @noindent Interfacing can be done at 3 levels: simple data, subprograms, and classes. In the first two cases, GNAT offers a specific @code{Convention C_Plus_Plus} (or @code{CPP}) that behaves exactly like @code{Convention C}. Usually, C++ mangles the names of subprograms. To generate proper mangled names automatically, see @ref{Generating Ada Bindings for C and C++ headers}). This problem can also be addressed manually in two ways: @itemize @bullet @item by modifying the C++ code in order to force a C convention using the @code{extern "C"} syntax. @item by figuring out the mangled name (using e.g. @command{nm}) and using it as the Link_Name argument of the pragma import. @end itemize @noindent Interfacing at the class level can be achieved by using the GNAT specific pragmas such as @code{CPP_Constructor}. @xref{Interfacing to C++,,, gnat_rm, GNAT Reference Manual}, for additional information. @node Linking a Mixed C++ & Ada Program @subsection Linking a Mixed C++ & Ada Program @noindent Usually the linker of the C++ development system must be used to link mixed applications because most C++ systems will resolve elaboration issues (such as calling constructors on global class instances) transparently during the link phase. GNAT has been adapted to ease the use of a foreign linker for the last phase. Three cases can be considered: @enumerate @item Using GNAT and G++ (GNU C++ compiler) from the same GCC installation: The C++ linker can simply be called by using the C++ specific driver called @code{g++}. Note that if the C++ code uses inline functions, you will need to compile your C++ code with the @code{-fkeep-inline-functions} switch in order to provide an existing function implementation that the Ada code can link with. @smallexample $ g++ -c -fkeep-inline-functions file1.C $ g++ -c -fkeep-inline-functions file2.C $ gnatmake ada_unit -largs file1.o file2.o --LINK=g++ @end smallexample @item Using GNAT and G++ from two different GCC installations: If both compilers are on the @env{PATH}, the previous method may be used. It is important to note that environment variables such as @env{C_INCLUDE_PATH}, @env{GCC_EXEC_PREFIX}, @env{BINUTILS_ROOT}, and @env{GCC_ROOT} will affect both compilers at the same time and may make one of the two compilers operate improperly if set during invocation of the wrong compiler. It is also very important that the linker uses the proper @file{libgcc.a} GCC library -- that is, the one from the C++ compiler installation. The implicit link command as suggested in the @command{gnatmake} command from the former example can be replaced by an explicit link command with the full-verbosity option in order to verify which library is used: @smallexample $ gnatbind ada_unit $ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++ @end smallexample If there is a problem due to interfering environment variables, it can be worked around by using an intermediate script. The following example shows the proper script to use when GNAT has not been installed at its default location and g++ has been installed at its default location: @smallexample $ cat ./my_script #!/bin/sh unset BINUTILS_ROOT unset GCC_ROOT c++ $* $ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script @end smallexample @item Using a non-GNU C++ compiler: The commands previously described can be used to insure that the C++ linker is used. Nonetheless, you need to add a few more parameters to the link command line, depending on the exception mechanism used. If the @code{setjmp/longjmp} exception mechanism is used, only the paths to the libgcc libraries are required: @smallexample $ cat ./my_script #!/bin/sh CC $* `gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a` $ gnatlink ada_unit file1.o file2.o --LINK=./my_script @end smallexample Where CC is the name of the non-GNU C++ compiler. If the @code{zero cost} exception mechanism is used, and the platform supports automatic registration of exception tables (e.g.@: Solaris or IRIX), paths to more objects are required: @smallexample $ cat ./my_script #!/bin/sh CC `gcc -print-file-name=crtbegin.o` $* \ `gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a` \ `gcc -print-file-name=crtend.o` $ gnatlink ada_unit file1.o file2.o --LINK=./my_script @end smallexample If the @code{zero cost} exception mechanism is used, and the platform doesn't support automatic registration of exception tables (e.g.@: HP-UX, Tru64 or AIX), the simple approach described above will not work and a pre-linking phase using GNAT will be necessary. @end enumerate Another alternative is to use the @command{gprbuild} multi-language builder which has a large knowledge base and knows how to link Ada and C++ code together automatically in most cases. @node A Simple Example @subsection A Simple Example @noindent The following example, provided as part of the GNAT examples, shows how to achieve procedural interfacing between Ada and C++ in both directions. The C++ class A has two methods. The first method is exported to Ada by the means of an extern C wrapper function. The second method calls an Ada subprogram. On the Ada side, The C++ calls are modelled by a limited record with a layout comparable to the C++ class. The Ada subprogram, in turn, calls the C++ method. So, starting from the C++ main program, the process passes back and forth between the two languages. @noindent Here are the compilation commands: @smallexample $ gnatmake -c simple_cpp_interface $ g++ -c cpp_main.C $ g++ -c ex7.C $ gnatbind -n simple_cpp_interface $ gnatlink simple_cpp_interface -o cpp_main --LINK=g++ -lstdc++ ex7.o cpp_main.o @end smallexample @noindent Here are the corresponding sources: @smallexample //cpp_main.C #include "ex7.h" extern "C" @{ void adainit (void); void adafinal (void); void method1 (A *t); @} void method1 (A *t) @{ t->method1 (); @} int main () @{ A obj; adainit (); obj.method2 (3030); adafinal (); @} //ex7.h class Origin @{ public: int o_value; @}; class A : public Origin @{ public: void method1 (void); void method2 (int v); A(); int a_value; @}; //ex7.C #include "ex7.h" #include extern "C" @{ void ada_method2 (A *t, int v);@} void A::method1 (void) @{ a_value = 2020; printf ("in A::method1, a_value = %d \n",a_value); @} void A::method2 (int v) @{ ada_method2 (this, v); printf ("in A::method2, a_value = %d \n",a_value); @} A::A(void) @{ a_value = 1010; printf ("in A::A, a_value = %d \n",a_value); @} @end smallexample @smallexample @c ada -- Ada sources package body Simple_Cpp_Interface is procedure Ada_Method2 (This : in out A; V : Integer) is begin Method1 (This); This.A_Value := V; end Ada_Method2; end Simple_Cpp_Interface; with System; package Simple_Cpp_Interface is type A is limited record Vptr : System.Address; O_Value : Integer; A_Value : Integer; end record; pragma Convention (C, A); procedure Method1 (This : in out A); pragma Import (C, Method1); procedure Ada_Method2 (This : in out A; V : Integer); pragma Export (C, Ada_Method2); end Simple_Cpp_Interface; @end smallexample @node Interfacing with C++ constructors @subsection Interfacing with C++ constructors @noindent In order to interface with C++ constructors GNAT provides the @code{pragma CPP_Constructor} (@xref{Interfacing to C++,,, gnat_rm, GNAT Reference Manual}, for additional information). In this section we present some common uses of C++ constructors in mixed-languages programs in GNAT. Let us assume that we need to interface with the following C++ class: @smallexample @b{class} Root @{ @b{public}: int a_value; int b_value; @b{virtual} int Get_Value (); Root(); // Default constructor Root(int v); // 1st non-default constructor Root(int v, int w); // 2nd non-default constructor @}; @end smallexample For this purpose we can write the following package spec (further information on how to build this spec is available in @ref{Interfacing with C++ at the Class Level} and @ref{Generating Ada Bindings for C and C++ headers}). @smallexample @c ada with Interfaces.C; use Interfaces.C; package Pkg_Root is type Root is tagged limited record A_Value : int; B_Value : int; end record; pragma Import (CPP, Root); function Get_Value (Obj : Root) return int; pragma Import (CPP, Get_Value); function Constructor return Root; pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ev"); function Constructor (v : Integer) return Root; pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ei"); function Constructor (v, w : Integer) return Root; pragma Cpp_Constructor (Constructor, "_ZN4RootC1Eii"); end Pkg_Root; @end smallexample On the Ada side the constructor is represented by a function (whose name is arbitrary) that returns the classwide type corresponding to the imported C++ class. Although the constructor is described as a function, it is typically a procedure with an extra implicit argument (the object being initialized) at the implementation level. GNAT issues the appropriate call, whatever it is, to get the object properly initialized. Constructors can only appear in the following contexts: @itemize @bullet @item On the right side of an initialization of an object of type @var{T}. @item On the right side of an initialization of a record component of type @var{T}. @item In an Ada 2005 limited aggregate. @item In an Ada 2005 nested limited aggregate. @item In an Ada 2005 limited aggregate that initializes an object built in place by an extended return statement. @end itemize @noindent In a declaration of an object whose type is a class imported from C++, either the default C++ constructor is implicitly called by GNAT, or else the required C++ constructor must be explicitly called in the expression that initializes the object. For example: @smallexample @c ada Obj1 : Root; Obj2 : Root := Constructor; Obj3 : Root := Constructor (v => 10); Obj4 : Root := Constructor (30, 40); @end smallexample The first two declarations are equivalent: in both cases the default C++ constructor is invoked (in the former case the call to the constructor is implicit, and in the latter case the call is explicit in the object declaration). @code{Obj3} is initialized by the C++ non-default constructor that takes an integer argument, and @code{Obj4} is initialized by the non-default C++ constructor that takes two integers. Let us derive the imported C++ class in the Ada side. For example: @smallexample @c ada type DT is new Root with record C_Value : Natural := 2009; end record; @end smallexample In this case the components DT inherited from the C++ side must be initialized by a C++ constructor, and the additional Ada components of type DT are initialized by GNAT. The initialization of such an object is done either by default, or by means of a function returning an aggregate of type DT, or by means of an extension aggregate. @smallexample @c ada Obj5 : DT; Obj6 : DT := Function_Returning_DT (50); Obj7 : DT := (Constructor (30,40) with C_Value => 50); @end smallexample The declaration of @code{Obj5} invokes the default constructors: the C++ default constructor of the parent type takes care of the initialization of the components inherited from Root, and GNAT takes care of the default initialization of the additional Ada components of type DT (that is, @code{C_Value} is initialized to value 2009). The order of invocation of the constructors is consistent with the order of elaboration required by Ada and C++. That is, the constructor of the parent type is always called before the constructor of the derived type. Let us now consider a record that has components whose type is imported from C++. For example: @smallexample @c ada type Rec1 is limited record Data1 : Root := Constructor (10); Value : Natural := 1000; end record; type Rec2 (D : Integer := 20) is limited record Rec : Rec1; Data2 : Root := Constructor (D, 30); end record; @end smallexample The initialization of an object of type @code{Rec2} will call the non-default C++ constructors specified for the imported components. For example: @smallexample @c ada Obj8 : Rec2 (40); @end smallexample Using Ada 2005 we can use limited aggregates to initialize an object invoking C++ constructors that differ from those specified in the type declarations. For example: @smallexample @c ada Obj9 : Rec2 := (Rec => (Data1 => Constructor (15, 16), others => <>), others => <>); @end smallexample The above declaration uses an Ada 2005 limited aggregate to initialize @code{Obj9}, and the C++ constructor that has two integer arguments is invoked to initialize the @code{Data1} component instead of the constructor specified in the declaration of type @code{Rec1}. In Ada 2005 the box in the aggregate indicates that unspecified components are initialized using the expression (if any) available in the component declaration. That is, in this case discriminant @code{D} is initialized to value @code{20}, @code{Value} is initialized to value 1000, and the non-default C++ constructor that handles two integers takes care of initializing component @code{Data2} with values @code{20,30}. In Ada 2005 we can use the extended return statement to build the Ada equivalent to C++ non-default constructors. For example: @smallexample @c ada function Constructor (V : Integer) return Rec2 is begin return Obj : Rec2 := (Rec => (Data1 => Constructor (V, 20), others => <>), others => <>) do -- Further actions required for construction of -- objects of type Rec2 ... end record; end Constructor; @end smallexample In this example the extended return statement construct is used to build in place the returned object whose components are initialized by means of a limited aggregate. Any further action associated with the constructor can be placed inside the construct. @node Interfacing with C++ at the Class Level @subsection Interfacing with C++ at the Class Level @noindent In this section we demonstrate the GNAT features for interfacing with C++ by means of an example making use of Ada 2005 abstract interface types. This example consists of a classification of animals; classes have been used to model our main classification of animals, and interfaces provide support for the management of secondary classifications. We first demonstrate a case in which the types and constructors are defined on the C++ side and imported from the Ada side, and latter the reverse case. The root of our derivation will be the @code{Animal} class, with a single private attribute (the @code{Age} of the animal) and two public primitives to set and get the value of this attribute. @smallexample @b{class} Animal @{ @b{public}: @b{virtual} void Set_Age (int New_Age); @b{virtual} int Age (); @b{private}: int Age_Count; @}; @end smallexample Abstract interface types are defined in C++ by means of classes with pure virtual functions and no data members. In our example we will use two interfaces that provide support for the common management of @code{Carnivore} and @code{Domestic} animals: @smallexample @b{class} Carnivore @{ @b{public}: @b{virtual} int Number_Of_Teeth () = 0; @}; @b{class} Domestic @{ @b{public}: @b{virtual void} Set_Owner (char* Name) = 0; @}; @end smallexample Using these declarations, we can now say that a @code{Dog} is an animal that is both Carnivore and Domestic, that is: @smallexample @b{class} Dog : Animal, Carnivore, Domestic @{ @b{public}: @b{virtual} int Number_Of_Teeth (); @b{virtual} void Set_Owner (char* Name); Dog(); // Constructor @b{private}: int Tooth_Count; char *Owner; @}; @end smallexample In the following examples we will assume that the previous declarations are located in a file named @code{animals.h}. The following package demonstrates how to import these C++ declarations from the Ada side: @smallexample @c ada with Interfaces.C.Strings; use Interfaces.C.Strings; package Animals is type Carnivore is interface; pragma Convention (C_Plus_Plus, Carnivore); function Number_Of_Teeth (X : Carnivore) return Natural is abstract; type Domestic is interface; pragma Convention (C_Plus_Plus, Set_Owner); procedure Set_Owner (X : in out Domestic; Name : Chars_Ptr) is abstract; type Animal is tagged record Age : Natural := 0; end record; pragma Import (C_Plus_Plus, Animal); procedure Set_Age (X : in out Animal; Age : Integer); pragma Import (C_Plus_Plus, Set_Age); function Age (X : Animal) return Integer; pragma Import (C_Plus_Plus, Age); type Dog is new Animal and Carnivore and Domestic with record Tooth_Count : Natural; Owner : String (1 .. 30); end record; pragma Import (C_Plus_Plus, Dog); function Number_Of_Teeth (A : Dog) return Integer; pragma Import (C_Plus_Plus, Number_Of_Teeth); procedure Set_Owner (A : in out Dog; Name : Chars_Ptr); pragma Import (C_Plus_Plus, Set_Owner); function New_Dog return Dog; pragma CPP_Constructor (New_Dog); pragma Import (CPP, New_Dog, "_ZN3DogC2Ev"); end Animals; @end smallexample Thanks to the compatibility between GNAT run-time structures and the C++ ABI, interfacing with these C++ classes is easy. The only requirement is that all the primitives and components must be declared exactly in the same order in the two languages. Regarding the abstract interfaces, we must indicate to the GNAT compiler by means of a @code{pragma Convention (C_Plus_Plus)}, the convention used to pass the arguments to the called primitives will be the same as for C++. For the imported classes we use @code{pragma Import} with convention @code{C_Plus_Plus} to indicate that they have been defined on the C++ side; this is required because the dispatch table associated with these tagged types will be built in the C++ side and therefore will not contain the predefined Ada primitives which Ada would otherwise expect. As the reader can see there is no need to indicate the C++ mangled names associated with each subprogram because it is assumed that all the calls to these primitives will be dispatching calls. The only exception is the constructor, which must be registered with the compiler by means of @code{pragma CPP_Constructor} and needs to provide its associated C++ mangled name because the Ada compiler generates direct calls to it. With the above packages we can now declare objects of type Dog on the Ada side and dispatch calls to the corresponding subprograms on the C++ side. We can also extend the tagged type Dog with further fields and primitives, and override some of its C++ primitives on the Ada side. For example, here we have a type derivation defined on the Ada side that inherits all the dispatching primitives of the ancestor from the C++ side. @smallexample @b{with} Animals; @b{use} Animals; @b{package} Vaccinated_Animals @b{is} @b{type} Vaccinated_Dog @b{is new} Dog @b{with null record}; @b{function} Vaccination_Expired (A : Vaccinated_Dog) @b{return} Boolean; @b{end} Vaccinated_Animals; @end smallexample It is important to note that, because of the ABI compatibility, the programmer does not need to add any further information to indicate either the object layout or the dispatch table entry associated with each dispatching operation. Now let us define all the types and constructors on the Ada side and export them to C++, using the same hierarchy of our previous example: @smallexample @c ada with Interfaces.C.Strings; use Interfaces.C.Strings; package Animals is type Carnivore is interface; pragma Convention (C_Plus_Plus, Carnivore); function Number_Of_Teeth (X : Carnivore) return Natural is abstract; type Domestic is interface; pragma Convention (C_Plus_Plus, Set_Owner); procedure Set_Owner (X : in out Domestic; Name : Chars_Ptr) is abstract; type Animal is tagged record Age : Natural := 0; end record; pragma Convention (C_Plus_Plus, Animal); procedure Set_Age (X : in out Animal; Age : Integer); pragma Export (C_Plus_Plus, Set_Age); function Age (X : Animal) return Integer; pragma Export (C_Plus_Plus, Age); type Dog is new Animal and Carnivore and Domestic with record Tooth_Count : Natural; Owner : String (1 .. 30); end record; pragma Convention (C_Plus_Plus, Dog); function Number_Of_Teeth (A : Dog) return Integer; pragma Export (C_Plus_Plus, Number_Of_Teeth); procedure Set_Owner (A : in out Dog; Name : Chars_Ptr); pragma Export (C_Plus_Plus, Set_Owner); function New_Dog return Dog'Class; pragma Export (C_Plus_Plus, New_Dog); end Animals; @end smallexample Compared with our previous example the only difference is the use of @code{pragma Export} to indicate to the GNAT compiler that the primitives will be available to C++. Thanks to the ABI compatibility, on the C++ side there is nothing else to be done; as explained above, the only requirement is that all the primitives and components are declared in exactly the same order. For completeness, let us see a brief C++ main program that uses the declarations available in @code{animals.h} (presented in our first example) to import and use the declarations from the Ada side, properly initializing and finalizing the Ada run-time system along the way: @smallexample @b{#include} "animals.h" @b{#include} @b{using namespace} std; void Check_Carnivore (Carnivore *obj) @{@dots{}@} void Check_Domestic (Domestic *obj) @{@dots{}@} void Check_Animal (Animal *obj) @{@dots{}@} void Check_Dog (Dog *obj) @{@dots{}@} @b{extern} "C" @{ void adainit (void); void adafinal (void); Dog* new_dog (); @} void test () @{ Dog *obj = new_dog(); // Ada constructor Check_Carnivore (obj); // Check secondary DT Check_Domestic (obj); // Check secondary DT Check_Animal (obj); // Check primary DT Check_Dog (obj); // Check primary DT @} int main () @{ adainit (); test(); adafinal (); return 0; @} @end smallexample @node Comparison between GNAT and C/C++ Compilation Models @section Comparison between GNAT and C/C++ Compilation Models @noindent The GNAT model of compilation is close to the C and C++ models. You can think of Ada specs as corresponding to header files in C. As in C, you don't need to compile specs; they are compiled when they are used. The Ada @code{with} is similar in effect to the @code{#include} of a C header. One notable difference is that, in Ada, you may compile specs separately to check them for semantic and syntactic accuracy. This is not always possible with C headers because they are fragments of programs that have less specific syntactic or semantic rules. The other major difference is the requirement for running the binder, which performs two important functions. First, it checks for consistency. In C or C++, the only defense against assembling inconsistent programs lies outside the compiler, in a makefile, for example. The binder satisfies the Ada requirement that it be impossible to construct an inconsistent program when the compiler is used in normal mode. @cindex Elaboration order control The other important function of the binder is to deal with elaboration issues. There are also elaboration issues in C++ that are handled automatically. This automatic handling has the advantage of being simpler to use, but the C++ programmer has no control over elaboration. Where @code{gnatbind} might complain there was no valid order of elaboration, a C++ compiler would simply construct a program that malfunctioned at run time. @end ifclear @node Comparison between GNAT and Conventional Ada Library Models @section Comparison between GNAT and Conventional Ada Library Models @noindent This section is intended for Ada programmers who have used an Ada compiler implementing the traditional Ada library model, as described in the Ada Reference Manual. @cindex GNAT library In GNAT, there is no ``library'' in the normal sense. Instead, the set of source files themselves acts as the library. Compiling Ada programs does not generate any centralized information, but rather an object file and a ALI file, which are of interest only to the binder and linker. In a traditional system, the compiler reads information not only from the source file being compiled, but also from the centralized library. This means that the effect of a compilation depends on what has been previously compiled. In particular: @itemize @bullet @item When a unit is @code{with}'ed, the unit seen by the compiler corresponds to the version of the unit most recently compiled into the library. @item Inlining is effective only if the necessary body has already been compiled into the library. @item Compiling a unit may obsolete other units in the library. @end itemize @noindent In GNAT, compiling one unit never affects the compilation of any other units because the compiler reads only source files. Only changes to source files can affect the results of a compilation. In particular: @itemize @bullet @item When a unit is @code{with}'ed, the unit seen by the compiler corresponds to the source version of the unit that is currently accessible to the compiler. @item @cindex Inlining Inlining requires the appropriate source files for the package or subprogram bodies to be available to the compiler. Inlining is always effective, independent of the order in which units are complied. @item Compiling a unit never affects any other compilations. The editing of sources may cause previous compilations to be out of date if they depended on the source file being modified. @end itemize @noindent The most important result of these differences is that order of compilation is never significant in GNAT. There is no situation in which one is required to do one compilation before another. What shows up as order of compilation requirements in the traditional Ada library becomes, in GNAT, simple source dependencies; in other words, there is only a set of rules saying what source files must be present when a file is compiled. @ifset vms @node Placement of temporary files @section Placement of temporary files @cindex Temporary files (user control over placement) @noindent GNAT creates temporary files in the directory designated by the environment variable @env{TMPDIR}. (See the HP @emph{C RTL Reference Manual} on the function @code{getenv()} for detailed information on how environment variables are resolved. For most users the easiest way to make use of this feature is to simply define @env{TMPDIR} as a job level logical name). For example, if you wish to use a Ramdisk (assuming DECRAM is installed) for compiler temporary files, then you can include something like the following command in your @file{LOGIN.COM} file: @smallexample $ define/job TMPDIR "/disk$scratchram/000000/temp/" @end smallexample @noindent If @env{TMPDIR} is not defined, then GNAT uses the directory designated by @env{TMP}; if @env{TMP} is not defined, then GNAT uses the directory designated by @env{TEMP}. If none of these environment variables are defined then GNAT uses the directory designated by the logical name @code{SYS$SCRATCH:} (by default the user's home directory). If all else fails GNAT uses the current directory for temporary files. @end ifset @c ************************* @node Compiling Using gcc @chapter Compiling Using @command{gcc} @noindent This chapter discusses how to compile Ada programs using the @command{gcc} command. It also describes the set of switches that can be used to control the behavior of the compiler. @menu * Compiling Programs:: * Switches for gcc:: * Search Paths and the Run-Time Library (RTL):: * Order of Compilation Issues:: * Examples:: @end menu @node Compiling Programs @section Compiling Programs @noindent The first step in creating an executable program is to compile the units of the program using the @command{gcc} command. You must compile the following files: @itemize @bullet @item the body file (@file{.adb}) for a library level subprogram or generic subprogram @item the spec file (@file{.ads}) for a library level package or generic package that has no body @item the body file (@file{.adb}) for a library level package or generic package that has a body @end itemize @noindent You need @emph{not} compile the following files @itemize @bullet @item the spec of a library unit which has a body @item subunits @end itemize @noindent because they are compiled as part of compiling related units. GNAT package specs when the corresponding body is compiled, and subunits when the parent is compiled. @cindex cannot generate code If you attempt to compile any of these files, you will get one of the following error messages (where @var{fff} is the name of the file you compiled): @smallexample cannot generate code for file @var{fff} (package spec) to check package spec, use -gnatc cannot generate code for file @var{fff} (missing subunits) to check parent unit, use -gnatc cannot generate code for file @var{fff} (subprogram spec) to check subprogram spec, use -gnatc cannot generate code for file @var{fff} (subunit) to check subunit, use -gnatc @end smallexample @noindent As indicated by the above error messages, if you want to submit one of these files to the compiler to check for correct semantics without generating code, then use the @option{-gnatc} switch. The basic command for compiling a file containing an Ada unit is @smallexample @c $ gcc -c @ovar{switches} @file{file name} @c Expanding @ovar macro inline (explanation in macro def comments) $ gcc -c @r{[}@var{switches}@r{]} @file{file name} @end smallexample @noindent where @var{file name} is the name of the Ada file (usually having an extension @file{.ads} for a spec or @file{.adb} for a body). @ifclear vms You specify the @option{-c} switch to tell @command{gcc} to compile, but not link, the file. @end ifclear The result of a successful compilation is an object file, which has the same name as the source file but an extension of @file{.o} and an Ada Library Information (ALI) file, which also has the same name as the source file, but with @file{.ali} as the extension. GNAT creates these two output files in the current directory, but you may specify a source file in any directory using an absolute or relative path specification containing the directory information. @findex gnat1 @command{gcc} is actually a driver program that looks at the extensions of the file arguments and loads the appropriate compiler. For example, the GNU C compiler is @file{cc1}, and the Ada compiler is @file{gnat1}. These programs are in directories known to the driver program (in some configurations via environment variables you set), but need not be in your path. The @command{gcc} driver also calls the assembler and any other utilities needed to complete the generation of the required object files. It is possible to supply several file names on the same @command{gcc} command. This causes @command{gcc} to call the appropriate compiler for each file. For example, the following command lists three separate files to be compiled: @smallexample $ gcc -c x.adb y.adb z.c @end smallexample @noindent calls @code{gnat1} (the Ada compiler) twice to compile @file{x.adb} and @file{y.adb}, and @code{cc1} (the C compiler) once to compile @file{z.c}. The compiler generates three object files @file{x.o}, @file{y.o} and @file{z.o} and the two ALI files @file{x.ali} and @file{y.ali} from the Ada compilations. Any switches apply to all the files ^listed,^listed.^ @ifclear vms except for @option{-gnat@var{x}} switches, which apply only to Ada compilations. @end ifclear @node Switches for gcc @section Switches for @command{gcc} @noindent The @command{gcc} command accepts switches that control the compilation process. These switches are fully described in this section. First we briefly list all the switches, in alphabetical order, then we describe the switches in more detail in functionally grouped sections. More switches exist for GCC than those documented here, especially for specific targets. However, their use is not recommended as they may change code generation in ways that are incompatible with the Ada run-time library, or can cause inconsistencies between compilation units. @menu * Output and Error Message Control:: * Warning Message Control:: * Debugging and Assertion Control:: * Validity Checking:: * Style Checking:: * Run-Time Checks:: * Using gcc for Syntax Checking:: * Using gcc for Semantic Checking:: * Compiling Different Versions of Ada:: * Character Set Control:: * File Naming Control:: * Subprogram Inlining Control:: * Auxiliary Output Control:: * Debugging Control:: * Exception Handling Control:: * Units to Sources Mapping Files:: * Integrated Preprocessing:: * Code Generation Control:: @ifset vms * Return Codes:: @end ifset @end menu @table @option @c !sort! @ifclear vms @cindex @option{-b} (@command{gcc}) @item -b @var{target} Compile your program to run on @var{target}, which is the name of a system configuration. You must have a GNAT cross-compiler built if @var{target} is not the same as your host system. @item -B@var{dir} @cindex @option{-B} (@command{gcc}) Load compiler executables (for example, @code{gnat1}, the Ada compiler) from @var{dir} instead of the default location. Only use this switch when multiple versions of the GNAT compiler are available. @xref{Directory Options,, Options for Directory Search, gcc, Using the GNU Compiler Collection (GCC)}, for further details. You would normally use the @option{-b} or @option{-V} switch instead. @item -c @cindex @option{-c} (@command{gcc}) Compile. Always use this switch when compiling Ada programs. Note: for some other languages when using @command{gcc}, notably in the case of C and C++, it is possible to use use @command{gcc} without a @option{-c} switch to compile and link in one step. In the case of GNAT, you cannot use this approach, because the binder must be run and @command{gcc} cannot be used to run the GNAT binder. @end ifclear @item -fno-inline @cindex @option{-fno-inline} (@command{gcc}) Suppresses all back-end inlining, even if other optimization or inlining switches are set. This includes suppression of inlining that results from the use of the pragma @code{Inline_Always}. Any occurrences of pragma @code{Inline} or @code{Inline_Always} are ignored, and @option{-gnatn} and @option{-gnatN} have no effect if this switch is present. @item -fno-inline-functions @cindex @option{-fno-inline-functions} (@command{gcc}) Suppresses automatic inlining of subprograms, which is enabled if @option{-O3} is used. @item -fno-inline-small-functions @cindex @option{-fno-inline-small-functions} (@command{gcc}) Suppresses automatic inlining of small subprograms, which is enabled if @option{-O2} is used. @item -fno-inline-functions-called-once @cindex @option{-fno-inline-functions-called-once} (@command{gcc}) Suppresses inlining of subprograms local to the unit and called once from within it, which is enabled if @option{-O1} is used. @item -fno-ivopts @cindex @option{-fno-ivopts} (@command{gcc}) Suppresses high-level loop induction variable optimizations, which are enabled if @option{-O1} is used. These optimizations are generally profitable but, for some specific cases of loops with numerous uses of the iteration variable that follow a common pattern, they may end up destroying the regularity that could be exploited at a lower level and thus producing inferior code. @item -fno-strict-aliasing @cindex @option{-fno-strict-aliasing} (@command{gcc}) Causes the compiler to avoid assumptions regarding non-aliasing of objects of different types. See @ref{Optimization and Strict Aliasing} for details. @item -fstack-check @cindex @option{-fstack-check} (@command{gcc}) Activates stack checking. See @ref{Stack Overflow Checking} for details. @item -fstack-usage @cindex @option{-fstack-usage} (@command{gcc}) Makes the compiler output stack usage information for the program, on a per-function basis. See @ref{Static Stack Usage Analysis} for details. @item -fcallgraph-info@r{[}=su@r{]} @cindex @option{-fcallgraph-info} (@command{gcc}) Makes the compiler output callgraph information for the program, on a per-file basis. The information is generated in the VCG format. It can be decorated with stack-usage per-node information. @item ^-g^/DEBUG^ @cindex @option{^-g^/DEBUG^} (@command{gcc}) Generate debugging information. This information is stored in the object file and copied from there to the final executable file by the linker, where it can be read by the debugger. You must use the @option{^-g^/DEBUG^} switch if you plan on using the debugger. @item -gnat83 @cindex @option{-gnat83} (@command{gcc}) Enforce Ada 83 restrictions. @item -gnat95 @cindex @option{-gnat95} (@command{gcc}) Enforce Ada 95 restrictions. @item -gnat05 @cindex @option{-gnat05} (@command{gcc}) Allow full Ada 2005 features. @item -gnat2005 @cindex @option{-gnat2005} (@command{gcc}) Allow full Ada 2005 features (same as @option{-gnat05} @item -gnat12 @cindex @option{-gnat12} (@command{gcc}) @item -gnat2012 @cindex @option{-gnat2012} (@command{gcc}) Allow full Ada 2012 features (same as @option{-gnat12} @item -gnata @cindex @option{-gnata} (@command{gcc}) Assertions enabled. @code{Pragma Assert} and @code{pragma Debug} to be activated. Note that these pragmas can also be controlled using the configuration pragmas @code{Assertion_Policy} and @code{Debug_Policy}. It also activates pragmas @code{Check}, @code{Precondition}, and @code{Postcondition}. Note that these pragmas can also be controlled using the configuration pragma @code{Check_Policy}. @item -gnatA @cindex @option{-gnatA} (@command{gcc}) Avoid processing @file{gnat.adc}. If a @file{gnat.adc} file is present, it will be ignored. @item -gnatb @cindex @option{-gnatb} (@command{gcc}) Generate brief messages to @file{stderr} even if verbose mode set. @item -gnatB @cindex @option{-gnatB} (@command{gcc}) Assume no invalid (bad) values except for 'Valid attribute use (@pxref{Validity Checking}). @item -gnatc @cindex @option{-gnatc} (@command{gcc}) Check syntax and semantics only (no code generation attempted). @item -gnatC @cindex @option{-gnatC} (@command{gcc}) Generate CodePeer information (no code generation attempted). This switch will generate an intermediate representation suitable for use by CodePeer (@file{.scil} files). This switch is not compatible with code generation (it will, among other things, disable some switches such as -gnatn, and enable others such as -gnata). @item -gnatd @cindex @option{-gnatd} (@command{gcc}) Specify debug options for the compiler. The string of characters after the @option{-gnatd} specify the specific debug options. The possible characters are 0-9, a-z, A-Z, optionally preceded by a dot. See compiler source file @file{debug.adb} for details of the implemented debug options. Certain debug options are relevant to applications programmers, and these are documented at appropriate points in this users guide. @ifclear vms @item -gnatD @cindex @option{-gnatD[nn]} (@command{gcc}) @end ifclear @ifset vms @item /XDEBUG /LXDEBUG=nnn @end ifset Create expanded source files for source level debugging. This switch also suppress generation of cross-reference information (see @option{-gnatx}). @item -gnatec=@var{path} @cindex @option{-gnatec} (@command{gcc}) Specify a configuration pragma file @ifclear vms (the equal sign is optional) @end ifclear (@pxref{The Configuration Pragmas Files}). @item ^-gnateD^/DATA_PREPROCESSING=^symbol@r{[}=@var{value}@r{]} @cindex @option{-gnateD} (@command{gcc}) Defines a symbol, associated with @var{value}, for preprocessing. (@pxref{Integrated Preprocessing}). @item -gnatef @cindex @option{-gnatef} (@command{gcc}) Display full source path name in brief error messages. @item -gnateG @cindex @option{-gnateG} (@command{gcc}) Save result of preprocessing in a text file. @item -gnatem=@var{path} @cindex @option{-gnatem} (@command{gcc}) Specify a mapping file @ifclear vms (the equal sign is optional) @end ifclear (@pxref{Units to Sources Mapping Files}). @item -gnatep=@var{file} @cindex @option{-gnatep} (@command{gcc}) Specify a preprocessing data file @ifclear vms (the equal sign is optional) @end ifclear (@pxref{Integrated Preprocessing}). @item -gnateS @cindex @option{-gnateS} (@command{gcc}) Generate SCO (Source Coverage Obligation) information in the ALI file. This information is used by advanced coverage tools. See unit @file{SCOs} in the compiler sources for details in files @file{scos.ads} and @file{scos.adb}. @item -gnatE @cindex @option{-gnatE} (@command{gcc}) Full dynamic elaboration checks. @item -gnatf @cindex @option{-gnatf} (@command{gcc}) Full errors. Multiple errors per line, all undefined references, do not attempt to suppress cascaded errors. @item -gnatF @cindex @option{-gnatF} (@command{gcc}) Externals names are folded to all uppercase. @item ^-gnatg^/GNAT_INTERNAL^ @cindex @option{^-gnatg^/GNAT_INTERNAL^} (@command{gcc}) Internal GNAT implementation mode. This should not be used for applications programs, it is intended only for use by the compiler and its run-time library. For documentation, see the GNAT sources. Note that @option{^-gnatg^/GNAT_INTERNAL^} implies @option{^-gnatwae^/WARNINGS=ALL,ERRORS^} and @option{^-gnatyg^/STYLE_CHECKS=GNAT^} so that all standard warnings and all standard style options are turned on. All warnings and style messages are treated as errors. @ifclear vms @item -gnatG=nn @cindex @option{-gnatG[nn]} (@command{gcc}) @end ifclear @ifset vms @item /EXPAND_SOURCE, /LEXPAND_SOURCE=nnn @end ifset List generated expanded code in source form. @item ^-gnath^/HELP^ @cindex @option{^-gnath^/HELP^} (@command{gcc}) Output usage information. The output is written to @file{stdout}. @item ^-gnati^/IDENTIFIER_CHARACTER_SET=^@var{c} @cindex @option{^-gnati^/IDENTIFIER_CHARACTER_SET^} (@command{gcc}) Identifier character set @ifclear vms (@var{c}=1/2/3/4/8/9/p/f/n/w). @end ifclear For details of the possible selections for @var{c}, see @ref{Character Set Control}. @item ^-gnatI^/IGNORE_REP_CLAUSES^ @cindex @option{^-gnatI^IGNORE_REP_CLAUSES^} (@command{gcc}) Ignore representation clauses. When this switch is used, representation clauses are treated as comments. This is useful when initially porting code where you want to ignore rep clause problems, and also for compiling foreign code (particularly for use with ASIS). The representation clauses that are ignored are: enumeration_representation_clause, record_representation_clause, and attribute_definition_clause for the following attributes: Address, Alignment, Bit_Order, Component_Size, Machine_Radix, Object_Size, Size, Small, Stream_Size, and Value_Size. Note that this option should be used only for compiling -- the code is likely to malfunction at run time. @item -gnatjnn @cindex @option{-gnatjnn} (@command{gcc}) Reformat error messages to fit on nn character lines @item -gnatk=@var{n} @cindex @option{-gnatk} (@command{gcc}) Limit file names to @var{n} (1-999) characters ^(@code{k} = krunch)^^. @item -gnatl @cindex @option{-gnatl} (@command{gcc}) Output full source listing with embedded error messages. @item -gnatL @cindex @option{-gnatL} (@command{gcc}) Used in conjunction with -gnatG or -gnatD to intersperse original source lines (as comment lines with line numbers) in the expanded source output. @item -gnatm=@var{n} @cindex @option{-gnatm} (@command{gcc}) Limit number of detected error or warning messages to @var{n} where @var{n} is in the range 1..999999. The default setting if no switch is given is 9999. If the number of warnings reaches this limit, then a message is output and further warnings are suppressed, but the compilation is continued. If the number of error messages reaches this limit, then a message is output and the compilation is abandoned. The equal sign here is optional. A value of zero means that no limit applies. @item -gnatn @cindex @option{-gnatn} (@command{gcc}) Activate inlining for subprograms for which pragma @code{Inline} is specified. This inlining is performed by the GCC back-end. @item -gnatN @cindex @option{-gnatN} (@command{gcc}) Activate front end inlining for subprograms for which pragma @code{Inline} is specified. This inlining is performed by the front end and will be visible in the @option{-gnatG} output. When using a gcc-based back end (in practice this means using any version of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of @option{-gnatN} is deprecated, and the use of @option{-gnatn} is preferred. Historically front end inlining was more extensive than the gcc back end inlining, but that is no longer the case. @item -gnato @cindex @option{-gnato} (@command{gcc}) Enable numeric overflow checking (which is not normally enabled by default). Note that division by zero is a separate check that is not controlled by this switch (division by zero checking is on by default). @item -gnatp @cindex @option{-gnatp} (@command{gcc}) Suppress all checks. See @ref{Run-Time Checks} for details. This switch has no effect if cancelled by a subsequent @option{-gnat-p} switch. @item -gnat-p @cindex @option{-gnat-p} (@command{gcc}) Cancel effect of previous @option{-gnatp} switch. @item -gnatP @cindex @option{-gnatP} (@command{gcc}) Enable polling. This is required on some systems (notably Windows NT) to obtain asynchronous abort and asynchronous transfer of control capability. @xref{Pragma Polling,,, gnat_rm, GNAT Reference Manual}, for full details. @item -gnatq @cindex @option{-gnatq} (@command{gcc}) Don't quit. Try semantics, even if parse errors. @item -gnatQ @cindex @option{-gnatQ} (@command{gcc}) Don't quit. Generate @file{ALI} and tree files even if illegalities. @item -gnatr @cindex @option{-gnatr} (@command{gcc}) Treat pragma Restrictions as Restriction_Warnings. @item ^-gnatR@r{[}0@r{/}1@r{/}2@r{/}3@r{[}s@r{]]}^/REPRESENTATION_INFO^ @cindex @option{-gnatR} (@command{gcc}) Output representation information for declared types and objects. @item -gnats @cindex @option{-gnats} (@command{gcc}) Syntax check only. @item -gnatS @cindex @option{-gnatS} (@command{gcc}) Print package Standard. @item -gnatt @cindex @option{-gnatt} (@command{gcc}) Generate tree output file. @item ^-gnatT^/TABLE_MULTIPLIER=^@var{nnn} @cindex @option{^-gnatT^/TABLE_MULTIPLIER^} (@command{gcc}) All compiler tables start at @var{nnn} times usual starting size. @item -gnatu @cindex @option{-gnatu} (@command{gcc}) List units for this compilation. @item -gnatU @cindex @option{-gnatU} (@command{gcc}) Tag all error messages with the unique string ``error:'' @item -gnatv @cindex @option{-gnatv} (@command{gcc}) Verbose mode. Full error output with source lines to @file{stdout}. @item -gnatV @cindex @option{-gnatV} (@command{gcc}) Control level of validity checking (@pxref{Validity Checking}). @item ^-gnatw@var{xxx}^/WARNINGS=(@var{option}@r{[},@dots{}@r{]})^ @cindex @option{^-gnatw^/WARNINGS^} (@command{gcc}) Warning mode where ^@var{xxx} is a string of option letters that^the list of options^ denotes the exact warnings that are enabled or disabled (@pxref{Warning Message Control}). @item ^-gnatW^/WIDE_CHARACTER_ENCODING=^@var{e} @cindex @option{^-gnatW^/WIDE_CHARACTER_ENCODING^} (@command{gcc}) Wide character encoding method @ifclear vms (@var{e}=n/h/u/s/e/8). @end ifclear @ifset vms (@var{e}=@code{BRACKETS, NONE, HEX, UPPER, SHIFT_JIS, EUC, UTF8}) @end ifset @item -gnatx @cindex @option{-gnatx} (@command{gcc}) Suppress generation of cross-reference information. @item -gnatX @cindex @option{-gnatX} (@command{gcc}) Enable GNAT implementation extensions and latest Ada version. @item ^-gnaty^/STYLE_CHECKS=(option,option@dots{})^ @cindex @option{^-gnaty^/STYLE_CHECKS^} (@command{gcc}) Enable built-in style checks (@pxref{Style Checking}). @item ^-gnatz^/DISTRIBUTION_STUBS=^@var{m} @cindex @option{^-gnatz^/DISTRIBUTION_STUBS^} (@command{gcc}) Distribution stub generation and compilation @ifclear vms (@var{m}=r/c for receiver/caller stubs). @end ifclear @ifset vms (@var{m}=@code{RECEIVER} or @code{CALLER} to specify the type of stubs to be generated and compiled). @end ifset @item ^-I^/SEARCH=^@var{dir} @cindex @option{^-I^/SEARCH^} (@command{gcc}) @cindex RTL Direct GNAT to search the @var{dir} directory for source files needed by the current compilation (@pxref{Search Paths and the Run-Time Library (RTL)}). @item ^-I-^/NOCURRENT_DIRECTORY^ @cindex @option{^-I-^/NOCURRENT_DIRECTORY^} (@command{gcc}) @cindex RTL Except for the source file named in the command line, do not look for source files in the directory containing the source file named in the command line (@pxref{Search Paths and the Run-Time Library (RTL)}). @ifclear vms @item -mbig-switch @cindex @option{-mbig-switch} (@command{gcc}) @cindex @code{case} statement (effect of @option{-mbig-switch} option) This standard gcc switch causes the compiler to use larger offsets in its jump table representation for @code{case} statements. This may result in less efficient code, but is sometimes necessary (for example on HP-UX targets) @cindex HP-UX and @option{-mbig-switch} option in order to compile large and/or nested @code{case} statements. @item -o @var{file} @cindex @option{-o} (@command{gcc}) This switch is used in @command{gcc} to redirect the generated object file and its associated ALI file. Beware of this switch with GNAT, because it may cause the object file and ALI file to have different names which in turn may confuse the binder and the linker. @end ifclear @item -nostdinc @cindex @option{-nostdinc} (@command{gcc}) Inhibit the search of the default location for the GNAT Run Time Library (RTL) source files. @item -nostdlib @cindex @option{-nostdlib} (@command{gcc}) Inhibit the search of the default location for the GNAT Run Time Library (RTL) ALI files. @ifclear vms @c @item -O@ovar{n} @c Expanding @ovar macro inline (explanation in macro def comments) @item -O@r{[}@var{n}@r{]} @cindex @option{-O} (@command{gcc}) @var{n} controls the optimization level. @table @asis @item n = 0 No optimization, the default setting if no @option{-O} appears @item n = 1 Normal optimization, the default if you specify @option{-O} without an operand. A good compromise between code quality and compilation time. @item n = 2 Extensive optimization, may improve execution time, possibly at the cost of substantially increased compilation time. @item n = 3 Same as @option{-O2}, and also includes inline expansion for small subprograms in the same unit. @item n = s Optimize space usage @end table @noindent See also @ref{Optimization Levels}. @end ifclear @ifset vms @item /NOOPTIMIZE @cindex @option{/NOOPTIMIZE} (@code{GNAT COMPILE}) Equivalent to @option{/OPTIMIZE=NONE}. This is the default behavior in the absence of an @option{/OPTIMIZE} qualifier. @item /OPTIMIZE@r{[}=(keyword@r{[},@dots{}@r{]})@r{]} @cindex @option{/OPTIMIZE} (@code{GNAT COMPILE}) Selects the level of optimization for your program. The supported keywords are as follows: @table @code @item ALL Perform most optimizations, including those that are expensive. This is the default if the @option{/OPTIMIZE} qualifier is supplied without keyword options. @item NONE Do not do any optimizations. Same as @code{/NOOPTIMIZE}. @item SOME Perform some optimizations, but omit ones that are costly. @item DEVELOPMENT Same as @code{SOME}. @item INLINING Full optimization as in @option{/OPTIMIZE=ALL}, and also attempts automatic inlining of small subprograms within a unit @item UNROLL_LOOPS Try to unroll loops. This keyword may be specified together with any keyword above other than @code{NONE}. Loop unrolling usually, but not always, improves the performance of programs. @item SPACE Optimize space usage @end table @noindent See also @ref{Optimization Levels}. @end ifset @ifclear vms @item -pass-exit-codes @cindex @option{-pass-exit-codes} (@command{gcc}) Catch exit codes from the compiler and use the most meaningful as exit status. @end ifclear @item --RTS=@var{rts-path} @cindex @option{--RTS} (@command{gcc}) Specifies the default location of the runtime library. Same meaning as the equivalent @command{gnatmake} flag (@pxref{Switches for gnatmake}). @item ^-S^/ASM^ @cindex @option{^-S^/ASM^} (@command{gcc}) ^Used in place of @option{-c} to^Used to^ cause the assembler source file to be generated, using @file{^.s^.S^} as the extension, instead of the object file. This may be useful if you need to examine the generated assembly code. @item ^-fverbose-asm^/VERBOSE_ASM^ @cindex @option{^-fverbose-asm^/VERBOSE_ASM^} (@command{gcc}) ^Used in conjunction with @option{-S}^Used in place of @option{/ASM}^ to cause the generated assembly code file to be annotated with variable names, making it significantly easier to follow. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@command{gcc}) Show commands generated by the @command{gcc} driver. Normally used only for debugging purposes or if you need to be sure what version of the compiler you are executing. @ifclear vms @item -V @var{ver} @cindex @option{-V} (@command{gcc}) Execute @var{ver} version of the compiler. This is the @command{gcc} version, not the GNAT version. @end ifclear @item ^-w^/NO_BACK_END_WARNINGS^ @cindex @option{-w} (@command{gcc}) Turn off warnings generated by the back end of the compiler. Use of this switch also causes the default for front end warnings to be set to suppress (as though @option{-gnatws} had appeared at the start of the options). @end table @ifclear vms @c Combining qualifiers does not work on VMS You may combine a sequence of GNAT switches into a single switch. For example, the combined switch @cindex Combining GNAT switches @smallexample -gnatofi3 @end smallexample @noindent is equivalent to specifying the following sequence of switches: @smallexample -gnato -gnatf -gnati3 @end smallexample @end ifclear @noindent The following restrictions apply to the combination of switches in this manner: @itemize @bullet @item The switch @option{-gnatc} if combined with other switches must come first in the string. @item The switch @option{-gnats} if combined with other switches must come first in the string. @item The switches ^^@option{/DISTRIBUTION_STUBS=},^ @option{-gnatzc} and @option{-gnatzr} may not be combined with any other switches, and only one of them may appear in the command line. @item The switch @option{-gnat-p} may not be combined with any other switch. @ifclear vms @item Once a ``y'' appears in the string (that is a use of the @option{-gnaty} switch), then all further characters in the switch are interpreted as style modifiers (see description of @option{-gnaty}). @item Once a ``d'' appears in the string (that is a use of the @option{-gnatd} switch), then all further characters in the switch are interpreted as debug flags (see description of @option{-gnatd}). @item Once a ``w'' appears in the string (that is a use of the @option{-gnatw} switch), then all further characters in the switch are interpreted as warning mode modifiers (see description of @option{-gnatw}). @item Once a ``V'' appears in the string (that is a use of the @option{-gnatV} switch), then all further characters in the switch are interpreted as validity checking options (@pxref{Validity Checking}). @item Option ``em'', ``ec'', ``ep'', ``l='' and ``R'' must be the last options in a combined list of options. @end ifclear @end itemize @node Output and Error Message Control @subsection Output and Error Message Control @findex stderr @noindent The standard default format for error messages is called ``brief format''. Brief format messages are written to @file{stderr} (the standard error file) and have the following form: @smallexample e.adb:3:04: Incorrect spelling of keyword "function" e.adb:4:20: ";" should be "is" @end smallexample @noindent The first integer after the file name is the line number in the file, and the second integer is the column number within the line. @ifclear vms @code{GPS} can parse the error messages and point to the referenced character. @end ifclear The following switches provide control over the error message format: @table @option @c !sort! @item -gnatv @cindex @option{-gnatv} (@command{gcc}) @findex stdout @ifclear vms The v stands for verbose. @end ifclear The effect of this setting is to write long-format error messages to @file{stdout} (the standard output file. The same program compiled with the @option{-gnatv} switch would generate: @smallexample @cartouche 3. funcion X (Q : Integer) | >>> Incorrect spelling of keyword "function" 4. return Integer; | >>> ";" should be "is" @end cartouche @end smallexample @noindent The vertical bar indicates the location of the error, and the @samp{>>>} prefix can be used to search for error messages. When this switch is used the only source lines output are those with errors. @item -gnatl @cindex @option{-gnatl} (@command{gcc}) @ifclear vms The @code{l} stands for list. @end ifclear This switch causes a full listing of the file to be generated. In the case where a body is compiled, the corresponding spec is also listed, along with any subunits. Typical output from compiling a package body @file{p.adb} might look like: @smallexample @c ada @cartouche Compiling: p.adb 1. package body p is 2. procedure a; 3. procedure a is separate; 4. begin 5. null | >>> missing ";" 6. end; Compiling: p.ads 1. package p is 2. pragma Elaborate_Body | >>> missing ";" 3. end p; Compiling: p-a.adb 1. separate p | >>> missing "(" 2. procedure a is 3. begin 4. null | >>> missing ";" 5. end; @end cartouche @end smallexample @noindent @findex stderr When you specify the @option{-gnatv} or @option{-gnatl} switches and standard output is redirected, a brief summary is written to @file{stderr} (standard error) giving the number of error messages and warning messages generated. @item -^gnatl^OUTPUT_FILE^=file @cindex @option{^-gnatl^OUTPUT_FILE^=fname} (@command{gcc}) This has the same effect as @option{-gnatl} except that the output is written to a file instead of to standard output. If the given name @file{fname} does not start with a period, then it is the full name of the file to be written. If @file{fname} is an extension, it is appended to the name of the file being compiled. For example, if file @file{xyz.adb} is compiled with @option{^-gnatl^OUTPUT_FILE^=.lst}, then the output is written to file ^xyz.adb.lst^xyz.adb_lst^. @item -gnatU @cindex @option{-gnatU} (@command{gcc}) This switch forces all error messages to be preceded by the unique string ``error:''. This means that error messages take a few more characters in space, but allows easy searching for and identification of error messages. @item -gnatb @cindex @option{-gnatb} (@command{gcc}) @ifclear vms The @code{b} stands for brief. @end ifclear This switch causes GNAT to generate the brief format error messages to @file{stderr} (the standard error file) as well as the verbose format message or full listing (which as usual is written to @file{stdout} (the standard output file). @item -gnatm=@var{n} @cindex @option{-gnatm} (@command{gcc}) @ifclear vms The @code{m} stands for maximum. @end ifclear @var{n} is a decimal integer in the range of 1 to 999999 and limits the number of error or warning messages to be generated. For example, using @option{-gnatm2} might yield @smallexample e.adb:3:04: Incorrect spelling of keyword "function" e.adb:5:35: missing ".." fatal error: maximum number of errors detected compilation abandoned @end smallexample @noindent The default setting if no switch is given is 9999. If the number of warnings reaches this limit, then a message is output and further warnings are suppressed, but the compilation is continued. If the number of error messages reaches this limit, then a message is output and the compilation is abandoned. A value of zero means that no limit applies. @noindent Note that the equal sign is optional, so the switches @option{-gnatm2} and @option{-gnatm=2} are equivalent. @item -gnatf @cindex @option{-gnatf} (@command{gcc}) @cindex Error messages, suppressing @ifclear vms The @code{f} stands for full. @end ifclear Normally, the compiler suppresses error messages that are likely to be redundant. This switch causes all error messages to be generated. In particular, in the case of references to undefined variables. If a given variable is referenced several times, the normal format of messages is @smallexample e.adb:7:07: "V" is undefined (more references follow) @end smallexample @noindent where the parenthetical comment warns that there are additional references to the variable @code{V}. Compiling the same program with the @option{-gnatf} switch yields @smallexample e.adb:7:07: "V" is undefined e.adb:8:07: "V" is undefined e.adb:8:12: "V" is undefined e.adb:8:16: "V" is undefined e.adb:9:07: "V" is undefined e.adb:9:12: "V" is undefined @end smallexample @noindent The @option{-gnatf} switch also generates additional information for some error messages. Some examples are: @itemize @bullet @item Details on possibly non-portable unchecked conversion @item List possible interpretations for ambiguous calls @item Additional details on incorrect parameters @end itemize @item -gnatjnn @cindex @option{-gnatjnn} (@command{gcc}) In normal operation mode (or if @option{-gnatj0} is used, then error messages with continuation lines are treated as though the continuation lines were separate messages (and so a warning with two continuation lines counts as three warnings, and is listed as three separate messages). If the @option{-gnatjnn} switch is used with a positive value for nn, then messages are output in a different manner. A message and all its continuation lines are treated as a unit, and count as only one warning or message in the statistics totals. Furthermore, the message is reformatted so that no line is longer than nn characters. @item -gnatq @cindex @option{-gnatq} (@command{gcc}) @ifclear vms The @code{q} stands for quit (really ``don't quit''). @end ifclear In normal operation mode, the compiler first parses the program and determines if there are any syntax errors. If there are, appropriate error messages are generated and compilation is immediately terminated. This switch tells GNAT to continue with semantic analysis even if syntax errors have been found. This may enable the detection of more errors in a single run. On the other hand, the semantic analyzer is more likely to encounter some internal fatal error when given a syntactically invalid tree. @item -gnatQ @cindex @option{-gnatQ} (@command{gcc}) In normal operation mode, the @file{ALI} file is not generated if any illegalities are detected in the program. The use of @option{-gnatQ} forces generation of the @file{ALI} file. This file is marked as being in error, so it cannot be used for binding purposes, but it does contain reasonably complete cross-reference information, and thus may be useful for use by tools (e.g., semantic browsing tools or integrated development environments) that are driven from the @file{ALI} file. This switch implies @option{-gnatq}, since the semantic phase must be run to get a meaningful ALI file. In addition, if @option{-gnatt} is also specified, then the tree file is generated even if there are illegalities. It may be useful in this case to also specify @option{-gnatq} to ensure that full semantic processing occurs. The resulting tree file can be processed by ASIS, for the purpose of providing partial information about illegal units, but if the error causes the tree to be badly malformed, then ASIS may crash during the analysis. When @option{-gnatQ} is used and the generated @file{ALI} file is marked as being in error, @command{gnatmake} will attempt to recompile the source when it finds such an @file{ALI} file, including with switch @option{-gnatc}. Note that @option{-gnatQ} has no effect if @option{-gnats} is specified, since ALI files are never generated if @option{-gnats} is set. @end table @node Warning Message Control @subsection Warning Message Control @cindex Warning messages @noindent In addition to error messages, which correspond to illegalities as defined in the Ada Reference Manual, the compiler detects two kinds of warning situations. First, the compiler considers some constructs suspicious and generates a warning message to alert you to a possible error. Second, if the compiler detects a situation that is sure to raise an exception at run time, it generates a warning message. The following shows an example of warning messages: @smallexample e.adb:4:24: warning: creation of object may raise Storage_Error e.adb:10:17: warning: static value out of range e.adb:10:17: warning: "Constraint_Error" will be raised at run time @end smallexample @noindent GNAT considers a large number of situations as appropriate for the generation of warning messages. As always, warnings are not definite indications of errors. For example, if you do an out-of-range assignment with the deliberate intention of raising a @code{Constraint_Error} exception, then the warning that may be issued does not indicate an error. Some of the situations for which GNAT issues warnings (at least some of the time) are given in the following list. This list is not complete, and new warnings are often added to subsequent versions of GNAT. The list is intended to give a general idea of the kinds of warnings that are generated. @itemize @bullet @item Possible infinitely recursive calls @item Out-of-range values being assigned @item Possible order of elaboration problems @item Assertions (pragma Assert) that are sure to fail @item Unreachable code @item Address clauses with possibly unaligned values, or where an attempt is made to overlay a smaller variable with a larger one. @item Fixed-point type declarations with a null range @item Direct_IO or Sequential_IO instantiated with a type that has access values @item Variables that are never assigned a value @item Variables that are referenced before being initialized @item Task entries with no corresponding @code{accept} statement @item Duplicate accepts for the same task entry in a @code{select} @item Objects that take too much storage @item Unchecked conversion between types of differing sizes @item Missing @code{return} statement along some execution path in a function @item Incorrect (unrecognized) pragmas @item Incorrect external names @item Allocation from empty storage pool @item Potentially blocking operation in protected type @item Suspicious parenthesization of expressions @item Mismatching bounds in an aggregate @item Attempt to return local value by reference @item Premature instantiation of a generic body @item Attempt to pack aliased components @item Out of bounds array subscripts @item Wrong length on string assignment @item Violations of style rules if style checking is enabled @item Unused @code{with} clauses @item @code{Bit_Order} usage that does not have any effect @item @code{Standard.Duration} used to resolve universal fixed expression @item Dereference of possibly null value @item Declaration that is likely to cause storage error @item Internal GNAT unit @code{with}'ed by application unit @item Values known to be out of range at compile time @item Unreferenced labels and variables @item Address overlays that could clobber memory @item Unexpected initialization when address clause present @item Bad alignment for address clause @item Useless type conversions @item Redundant assignment statements and other redundant constructs @item Useless exception handlers @item Accidental hiding of name by child unit @item Access before elaboration detected at compile time @item A range in a @code{for} loop that is known to be null or might be null @end itemize @noindent The following section lists compiler switches that are available to control the handling of warning messages. It is also possible to exercise much finer control over what warnings are issued and suppressed using the GNAT pragma Warnings, @xref{Pragma Warnings,,, gnat_rm, GNAT Reference manual}. @table @option @c !sort! @item -gnatwa @emph{Activate all optional errors.} @cindex @option{-gnatwa} (@command{gcc}) This switch activates most optional warning messages, see remaining list in this section for details on optional warning messages that can be individually controlled. The warnings that are not turned on by this switch are @option{-gnatwd} (implicit dereferencing), @option{-gnatwh} (hiding), @option{-gnatw.h} (holes (gaps) in record layouts) @option{-gnatwl} (elaboration warnings), @option{-gnatw.o} (warn on values set by out parameters ignored) and @option{-gnatwt} (tracking of deleted conditional code). All other optional warnings are turned on. @item -gnatwA @emph{Suppress all optional errors.} @cindex @option{-gnatwA} (@command{gcc}) This switch suppresses all optional warning messages, see remaining list in this section for details on optional warning messages that can be individually controlled. @item -gnatw.a @emph{Activate warnings on failing assertions.} @cindex @option{-gnatw.a} (@command{gcc}) @cindex Assert failures This switch activates warnings for assertions where the compiler can tell at compile time that the assertion will fail. Note that this warning is given even if assertions are disabled. The default is that such warnings are generated. @item -gnatw.A @emph{Suppress warnings on failing assertions.} @cindex @option{-gnatw.A} (@command{gcc}) @cindex Assert failures This switch suppresses warnings for assertions where the compiler can tell at compile time that the assertion will fail. @item -gnatwb @emph{Activate warnings on bad fixed values.} @cindex @option{-gnatwb} (@command{gcc}) @cindex Bad fixed values @cindex Fixed-point Small value @cindex Small value This switch activates warnings for static fixed-point expressions whose value is not an exact multiple of Small. Such values are implementation dependent, since an implementation is free to choose either of the multiples that surround the value. GNAT always chooses the closer one, but this is not required behavior, and it is better to specify a value that is an exact multiple, ensuring predictable execution. The default is that such warnings are not generated. @item -gnatwB @emph{Suppress warnings on bad fixed values.} @cindex @option{-gnatwB} (@command{gcc}) This switch suppresses warnings for static fixed-point expressions whose value is not an exact multiple of Small. @item -gnatw.b @emph{Activate warnings on biased representation.} @cindex @option{-gnatw.b} (@command{gcc}) @cindex Biased representation This switch activates warnings when a size clause, value size clause, component clause, or component size clause forces the use of biased representation for an integer type (e.g. representing a range of 10..11 in a single bit by using 0/1 to represent 10/11). The default is that such warnings are generated. @item -gnatw.B @emph{Suppress warnings on biased representation.} @cindex @option{-gnatwB} (@command{gcc}) This switch suppresses warnings for representation clauses that force the use of biased representation. @item -gnatwc @emph{Activate warnings on conditionals.} @cindex @option{-gnatwc} (@command{gcc}) @cindex Conditionals, constant This switch activates warnings for conditional expressions used in tests that are known to be True or False at compile time. The default is that such warnings are not generated. Note that this warning does not get issued for the use of boolean variables or constants whose values are known at compile time, since this is a standard technique for conditional compilation in Ada, and this would generate too many false positive warnings. This warning option also activates a special test for comparisons using the operators ``>='' and`` <=''. If the compiler can tell that only the equality condition is possible, then it will warn that the ``>'' or ``<'' part of the test is useless and that the operator could be replaced by ``=''. An example would be comparing a @code{Natural} variable <= 0. This warning option also generates warnings if one or both tests is optimized away in a membership test for integer values if the result can be determined at compile time. Range tests on enumeration types are not included, since it is common for such tests to include an end point. This warning can also be turned on using @option{-gnatwa}. @item -gnatwC @emph{Suppress warnings on conditionals.} @cindex @option{-gnatwC} (@command{gcc}) This switch suppresses warnings for conditional expressions used in tests that are known to be True or False at compile time. @item -gnatw.c @emph{Activate warnings on missing component clauses.} @cindex @option{-gnatw.c} (@command{gcc}) @cindex Component clause, missing This switch activates warnings for record components where a record representation clause is present and has component clauses for the majority, but not all, of the components. A warning is given for each component for which no component clause is present. This warning can also be turned on using @option{-gnatwa}. @item -gnatw.C @emph{Suppress warnings on missing component clauses.} @cindex @option{-gnatwC} (@command{gcc}) This switch suppresses warnings for record components that are missing a component clause in the situation described above. @item -gnatwd @emph{Activate warnings on implicit dereferencing.} @cindex @option{-gnatwd} (@command{gcc}) If this switch is set, then the use of a prefix of an access type in an indexed component, slice, or selected component without an explicit @code{.all} will generate a warning. With this warning enabled, access checks occur only at points where an explicit @code{.all} appears in the source code (assuming no warnings are generated as a result of this switch). The default is that such warnings are not generated. Note that @option{-gnatwa} does not affect the setting of this warning option. @item -gnatwD @emph{Suppress warnings on implicit dereferencing.} @cindex @option{-gnatwD} (@command{gcc}) @cindex Implicit dereferencing @cindex Dereferencing, implicit This switch suppresses warnings for implicit dereferences in indexed components, slices, and selected components. @item -gnatwe @emph{Treat warnings and style checks as errors.} @cindex @option{-gnatwe} (@command{gcc}) @cindex Warnings, treat as error This switch causes warning messages and style check messages to be treated as errors. The warning string still appears, but the warning messages are counted as errors, and prevent the generation of an object file. Note that this is the only -gnatw switch that affects the handling of style check messages. @item -gnatw.e @emph{Activate every optional warning} @cindex @option{-gnatw.e} (@command{gcc}) @cindex Warnings, activate every optional warning This switch activates all optional warnings, including those which are not activated by @code{-gnatwa}. @item -gnatwf @emph{Activate warnings on unreferenced formals.} @cindex @option{-gnatwf} (@command{gcc}) @cindex Formals, unreferenced This switch causes a warning to be generated if a formal parameter is not referenced in the body of the subprogram. This warning can also be turned on using @option{-gnatwa} or @option{-gnatwu}. The default is that these warnings are not generated. @item -gnatwF @emph{Suppress warnings on unreferenced formals.} @cindex @option{-gnatwF} (@command{gcc}) This switch suppresses warnings for unreferenced formal parameters. Note that the combination @option{-gnatwu} followed by @option{-gnatwF} has the effect of warning on unreferenced entities other than subprogram formals. @item -gnatwg @emph{Activate warnings on unrecognized pragmas.} @cindex @option{-gnatwg} (@command{gcc}) @cindex Pragmas, unrecognized This switch causes a warning to be generated if an unrecognized pragma is encountered. Apart from issuing this warning, the pragma is ignored and has no effect. This warning can also be turned on using @option{-gnatwa}. The default is that such warnings are issued (satisfying the Ada Reference Manual requirement that such warnings appear). @item -gnatwG @emph{Suppress warnings on unrecognized pragmas.} @cindex @option{-gnatwG} (@command{gcc}) This switch suppresses warnings for unrecognized pragmas. @item -gnatwh @emph{Activate warnings on hiding.} @cindex @option{-gnatwh} (@command{gcc}) @cindex Hiding of Declarations This switch activates warnings on hiding declarations. A declaration is considered hiding if it is for a non-overloadable entity, and it declares an entity with the same name as some other entity that is directly or use-visible. The default is that such warnings are not generated. Note that @option{-gnatwa} does not affect the setting of this warning option. @item -gnatwH @emph{Suppress warnings on hiding.} @cindex @option{-gnatwH} (@command{gcc}) This switch suppresses warnings on hiding declarations. @item -gnatw.h @emph{Activate warnings on holes/gaps in records.} @cindex @option{-gnatw.h} (@command{gcc}) @cindex Record Representation (gaps) This switch activates warnings on component clauses in record representation clauses that leave holes (gaps) in the record layout. If this warning option is active, then record representation clauses should specify a contiguous layout, adding unused fill fields if needed. Note that @option{-gnatwa} does not affect the setting of this warning option. @item -gnatw.H @emph{Suppress warnings on holes/gaps in records.} @cindex @option{-gnatw.H} (@command{gcc}) This switch suppresses warnings on component clauses in record representation clauses that leave holes (haps) in the record layout. @item -gnatwi @emph{Activate warnings on implementation units.} @cindex @option{-gnatwi} (@command{gcc}) This switch activates warnings for a @code{with} of an internal GNAT implementation unit, defined as any unit from the @code{Ada}, @code{Interfaces}, @code{GNAT}, ^^@code{DEC},^ or @code{System} hierarchies that is not documented in either the Ada Reference Manual or the GNAT Programmer's Reference Manual. Such units are intended only for internal implementation purposes and should not be @code{with}'ed by user programs. The default is that such warnings are generated This warning can also be turned on using @option{-gnatwa}. @item -gnatwI @emph{Disable warnings on implementation units.} @cindex @option{-gnatwI} (@command{gcc}) This switch disables warnings for a @code{with} of an internal GNAT implementation unit. @item -gnatw.i @emph{Activate warnings on overlapping actuals.} @cindex @option{-gnatw.i} (@command{gcc}) This switch enables a warning on statically detectable overlapping actuals in a subprogram call, when one of the actuals is an in-out parameter, and the types of the actuals are not by-copy types. The warning is off by default, and is not included under -gnatwa. @item -gnatw.I @emph{Disable warnings on overlapping actuals.} @cindex @option{-gnatw.I} (@command{gcc}) This switch disables warnings on overlapping actuals in a call.. @item -gnatwj @emph{Activate warnings on obsolescent features (Annex J).} @cindex @option{-gnatwj} (@command{gcc}) @cindex Features, obsolescent @cindex Obsolescent features If this warning option is activated, then warnings are generated for calls to subprograms marked with @code{pragma Obsolescent} and for use of features in Annex J of the Ada Reference Manual. In the case of Annex J, not all features are flagged. In particular use of the renamed packages (like @code{Text_IO}) and use of package @code{ASCII} are not flagged, since these are very common and would generate many annoying positive warnings. The default is that such warnings are not generated. This warning is also turned on by the use of @option{-gnatwa}. In addition to the above cases, warnings are also generated for GNAT features that have been provided in past versions but which have been superseded (typically by features in the new Ada standard). For example, @code{pragma Ravenscar} will be flagged since its function is replaced by @code{pragma Profile(Ravenscar)}. Note that this warning option functions differently from the restriction @code{No_Obsolescent_Features} in two respects. First, the restriction applies only to annex J features. Second, the restriction does flag uses of package @code{ASCII}. @item -gnatwJ @emph{Suppress warnings on obsolescent features (Annex J).} @cindex @option{-gnatwJ} (@command{gcc}) This switch disables warnings on use of obsolescent features. @item -gnatwk @emph{Activate warnings on variables that could be constants.} @cindex @option{-gnatwk} (@command{gcc}) This switch activates warnings for variables that are initialized but never modified, and then could be declared constants. The default is that such warnings are not given. This warning can also be turned on using @option{-gnatwa}. @item -gnatwK @emph{Suppress warnings on variables that could be constants.} @cindex @option{-gnatwK} (@command{gcc}) This switch disables warnings on variables that could be declared constants. @item -gnatwl @emph{Activate warnings for elaboration pragmas.} @cindex @option{-gnatwl} (@command{gcc}) @cindex Elaboration, warnings This switch activates warnings on missing @code{Elaborate_All} and @code{Elaborate} pragmas. See the section in this guide on elaboration checking for details on when such pragmas should be used. In dynamic elaboration mode, this switch generations warnings about the need to add elaboration pragmas. Note however, that if you blindly follow these warnings, and add @code{Elaborate_All} warnings wherever they are recommended, you basically end up with the equivalent of the static elaboration model, which may not be what you want for legacy code for which the static model does not work. For the static model, the messages generated are labeled "info:" (for information messages). They are not warnings to add elaboration pragmas, merely informational messages showing what implicit elaboration pragmas have been added, for use in analyzing elaboration circularity problems. Warnings are also generated if you are using the static mode of elaboration, and a @code{pragma Elaborate} is encountered. The default is that such warnings are not generated. This warning is not automatically turned on by the use of @option{-gnatwa}. @item -gnatwL @emph{Suppress warnings for elaboration pragmas.} @cindex @option{-gnatwL} (@command{gcc}) This switch suppresses warnings on missing Elaborate and Elaborate_All pragmas. See the section in this guide on elaboration checking for details on when such pragmas should be used. @item -gnatwm @emph{Activate warnings on modified but unreferenced variables.} @cindex @option{-gnatwm} (@command{gcc}) This switch activates warnings for variables that are assigned (using an initialization value or with one or more assignment statements) but whose value is never read. The warning is suppressed for volatile variables and also for variables that are renamings of other variables or for which an address clause is given. This warning can also be turned on using @option{-gnatwa}. The default is that these warnings are not given. @item -gnatwM @emph{Disable warnings on modified but unreferenced variables.} @cindex @option{-gnatwM} (@command{gcc}) This switch disables warnings for variables that are assigned or initialized, but never read. @item -gnatw.m @emph{Activate warnings on suspicious modulus values.} @cindex @option{-gnatw.m} (@command{gcc}) This switch activates warnings for modulus values that seem suspicious. The cases caught are where the size is the same as the modulus (e.g. a modulus of 7 with a size of 7 bits), and modulus values of 32 or 64 with no size clause. The guess in both cases is that 2**x was intended rather than x. The default is that these warnings are given. @item -gnatw.M @emph{Disable warnings on suspicious modulus values.} @cindex @option{-gnatw.M} (@command{gcc}) This switch disables warnings for suspicious modulus values. @item -gnatwn @emph{Set normal warnings mode.} @cindex @option{-gnatwn} (@command{gcc}) This switch sets normal warning mode, in which enabled warnings are issued and treated as warnings rather than errors. This is the default mode. the switch @option{-gnatwn} can be used to cancel the effect of an explicit @option{-gnatws} or @option{-gnatwe}. It also cancels the effect of the implicit @option{-gnatwe} that is activated by the use of @option{-gnatg}. @item -gnatwo @emph{Activate warnings on address clause overlays.} @cindex @option{-gnatwo} (@command{gcc}) @cindex Address Clauses, warnings This switch activates warnings for possibly unintended initialization effects of defining address clauses that cause one variable to overlap another. The default is that such warnings are generated. This warning can also be turned on using @option{-gnatwa}. @item -gnatwO @emph{Suppress warnings on address clause overlays.} @cindex @option{-gnatwO} (@command{gcc}) This switch suppresses warnings on possibly unintended initialization effects of defining address clauses that cause one variable to overlap another. @item -gnatw.o @emph{Activate warnings on modified but unreferenced out parameters.} @cindex @option{-gnatw.o} (@command{gcc}) This switch activates warnings for variables that are modified by using them as actuals for a call to a procedure with an out mode formal, where the resulting assigned value is never read. It is applicable in the case where there is more than one out mode formal. If there is only one out mode formal, the warning is issued by default (controlled by -gnatwu). The warning is suppressed for volatile variables and also for variables that are renamings of other variables or for which an address clause is given. The default is that these warnings are not given. Note that this warning is not included in -gnatwa, it must be activated explicitly. @item -gnatw.O @emph{Disable warnings on modified but unreferenced out parameters.} @cindex @option{-gnatw.O} (@command{gcc}) This switch suppresses warnings for variables that are modified by using them as actuals for a call to a procedure with an out mode formal, where the resulting assigned value is never read. @item -gnatwp @emph{Activate warnings on ineffective pragma Inlines.} @cindex @option{-gnatwp} (@command{gcc}) @cindex Inlining, warnings This switch activates warnings for failure of front end inlining (activated by @option{-gnatN}) to inline a particular call. There are many reasons for not being able to inline a call, including most commonly that the call is too complex to inline. The default is that such warnings are not given. This warning can also be turned on using @option{-gnatwa}. Warnings on ineffective inlining by the gcc back-end can be activated separately, using the gcc switch -Winline. @item -gnatwP @emph{Suppress warnings on ineffective pragma Inlines.} @cindex @option{-gnatwP} (@command{gcc}) This switch suppresses warnings on ineffective pragma Inlines. If the inlining mechanism cannot inline a call, it will simply ignore the request silently. @item -gnatw.p @emph{Activate warnings on parameter ordering.} @cindex @option{-gnatw.p} (@command{gcc}) @cindex Parameter order, warnings This switch activates warnings for cases of suspicious parameter ordering when the list of arguments are all simple identifiers that match the names of the formals, but are in a different order. The warning is suppressed if any use of named parameter notation is used, so this is the appropriate way to suppress a false positive (and serves to emphasize that the "misordering" is deliberate). The default is that such warnings are not given. This warning can also be turned on using @option{-gnatwa}. @item -gnatw.P @emph{Suppress warnings on parameter ordering.} @cindex @option{-gnatw.P} (@command{gcc}) This switch suppresses warnings on cases of suspicious parameter ordering. @item -gnatwq @emph{Activate warnings on questionable missing parentheses.} @cindex @option{-gnatwq} (@command{gcc}) @cindex Parentheses, warnings This switch activates warnings for cases where parentheses are not used and the result is potential ambiguity from a readers point of view. For example (not a > b) when a and b are modular means ((not a) > b) and very likely the programmer intended (not (a > b)). Similarly (-x mod 5) means (-(x mod 5)) and quite likely ((-x) mod 5) was intended. In such situations it seems best to follow the rule of always parenthesizing to make the association clear, and this warning switch warns if such parentheses are not present. The default is that these warnings are given. This warning can also be turned on using @option{-gnatwa}. @item -gnatwQ @emph{Suppress warnings on questionable missing parentheses.} @cindex @option{-gnatwQ} (@command{gcc}) This switch suppresses warnings for cases where the association is not clear and the use of parentheses is preferred. @item -gnatwr @emph{Activate warnings on redundant constructs.} @cindex @option{-gnatwr} (@command{gcc}) This switch activates warnings for redundant constructs. The following is the current list of constructs regarded as redundant: @itemize @bullet @item Assignment of an item to itself. @item Type conversion that converts an expression to its own type. @item Use of the attribute @code{Base} where @code{typ'Base} is the same as @code{typ}. @item Use of pragma @code{Pack} when all components are placed by a record representation clause. @item Exception handler containing only a reraise statement (raise with no operand) which has no effect. @item Use of the operator abs on an operand that is known at compile time to be non-negative @item Comparison of boolean expressions to an explicit True value. @end itemize This warning can also be turned on using @option{-gnatwa}. The default is that warnings for redundant constructs are not given. @item -gnatwR @emph{Suppress warnings on redundant constructs.} @cindex @option{-gnatwR} (@command{gcc}) This switch suppresses warnings for redundant constructs. @item -gnatw.r @emph{Activate warnings for object renaming function.} @cindex @option{-gnatw.r} (@command{gcc}) This switch activates warnings for an object renaming that renames a function call, which is equivalent to a constant declaration (as opposed to renaming the function itself). The default is that these warnings are given. This warning can also be turned on using @option{-gnatwa}. @item -gnatw.R @emph{Suppress warnings for object renaming function.} @cindex @option{-gnatwT} (@command{gcc}) This switch suppresses warnings for object renaming function. @item -gnatws @emph{Suppress all warnings.} @cindex @option{-gnatws} (@command{gcc}) This switch completely suppresses the output of all warning messages from the GNAT front end. Note that it does not suppress warnings from the @command{gcc} back end. To suppress these back end warnings as well, use the switch @option{-w} in addition to @option{-gnatws}. Also this switch has no effect on the handling of style check messages. @item -gnatw.s @emph{Activate warnings on overridden size clauses.} @cindex @option{-gnatw.s} (@command{gcc}) @cindex Record Representation (component sizes) This switch activates warnings on component clauses in record representation clauses where the length given overrides that specified by an explicit size clause for the component type. A warning is similarly given in the array case if a specified component size overrides an explicit size clause for the array component type. Note that @option{-gnatwa} does not affect the setting of this warning option. @item -gnatw.S @emph{Suppress warnings on overriddebn size clauses.} @cindex @option{-gnatw.S} (@command{gcc}) This switch suppresses warnings on component clauses in record representation clauses that override size clauses, and similar warnings when an array component size overrides a size clause. @item -gnatwt @emph{Activate warnings for tracking of deleted conditional code.} @cindex @option{-gnatwt} (@command{gcc}) @cindex Deactivated code, warnings @cindex Deleted code, warnings This switch activates warnings for tracking of code in conditionals (IF and CASE statements) that is detected to be dead code which cannot be executed, and which is removed by the front end. This warning is off by default, and is not turned on by @option{-gnatwa}, it has to be turned on explicitly. This may be useful for detecting deactivated code in certified applications. @item -gnatwT @emph{Suppress warnings for tracking of deleted conditional code.} @cindex @option{-gnatwT} (@command{gcc}) This switch suppresses warnings for tracking of deleted conditional code. @item -gnatwu @emph{Activate warnings on unused entities.} @cindex @option{-gnatwu} (@command{gcc}) This switch activates warnings to be generated for entities that are declared but not referenced, and for units that are @code{with}'ed and not referenced. In the case of packages, a warning is also generated if no entities in the package are referenced. This means that if the package is referenced but the only references are in @code{use} clauses or @code{renames} declarations, a warning is still generated. A warning is also generated for a generic package that is @code{with}'ed but never instantiated. In the case where a package or subprogram body is compiled, and there is a @code{with} on the corresponding spec that is only referenced in the body, a warning is also generated, noting that the @code{with} can be moved to the body. The default is that such warnings are not generated. This switch also activates warnings on unreferenced formals (it includes the effect of @option{-gnatwf}). This warning can also be turned on using @option{-gnatwa}. @item -gnatwU @emph{Suppress warnings on unused entities.} @cindex @option{-gnatwU} (@command{gcc}) This switch suppresses warnings for unused entities and packages. It also turns off warnings on unreferenced formals (and thus includes the effect of @option{-gnatwF}). @item -gnatw.u @emph{Activate warnings on unordered enumeration types.} @cindex @option{-gnatw.u} (@command{gcc}) This switch causes enumeration types to be considered as conceptually unordered, unless an explicit pragma @code{Ordered} is given for the type. The effect is to generate warnings in clients that use explicit comparisons or subranges, since these constructs both treat objects of the type as ordered. (A @emph{client} is defined as a unit that is other than the unit in which the type is declared, or its body or subunits.) Please refer to the description of pragma @code{Ordered} in the @cite{@value{EDITION} Reference Manual} for further details. @item -gnatw.U @emph{Deactivate warnings on unordered enumeration types.} @cindex @option{-gnatw.U} (@command{gcc}) This switch causes all enumeration types to be considered as ordered, so that no warnings are given for comparisons or subranges for any type. @item -gnatwv @emph{Activate warnings on unassigned variables.} @cindex @option{-gnatwv} (@command{gcc}) @cindex Unassigned variable warnings This switch activates warnings for access to variables which may not be properly initialized. The default is that such warnings are generated. This warning can also be turned on using @option{-gnatwa}. @item -gnatwV @emph{Suppress warnings on unassigned variables.} @cindex @option{-gnatwV} (@command{gcc}) This switch suppresses warnings for access to variables which may not be properly initialized. For variables of a composite type, the warning can also be suppressed in Ada 2005 by using a default initialization with a box. For example, if Table is an array of records whose components are only partially uninitialized, then the following code: @smallexample @c ada Tab : Table := (others => <>); @end smallexample will suppress warnings on subsequent statements that access components of variable Tab. @item -gnatww @emph{Activate warnings on wrong low bound assumption.} @cindex @option{-gnatww} (@command{gcc}) @cindex String indexing warnings This switch activates warnings for indexing an unconstrained string parameter with a literal or S'Length. This is a case where the code is assuming that the low bound is one, which is in general not true (for example when a slice is passed). The default is that such warnings are generated. This warning can also be turned on using @option{-gnatwa}. @item -gnatwW @emph{Suppress warnings on wrong low bound assumption.} @cindex @option{-gnatwW} (@command{gcc}) This switch suppresses warnings for indexing an unconstrained string parameter with a literal or S'Length. Note that this warning can also be suppressed in a particular case by adding an assertion that the lower bound is 1, as shown in the following example. @smallexample @c ada procedure K (S : String) is pragma Assert (S'First = 1); @dots{} @end smallexample @item -gnatw.w @emph{Activate warnings on unnecessary Warnings Off pragmas} @cindex @option{-gnatw.w} (@command{gcc}) @cindex Warnings Off control This switch activates warnings for use of @code{pragma Warnings (Off, entity} where either the pragma is entirely useless (because it suppresses no warnings), or it could be replaced by @code{pragma Unreferenced} or @code{pragma Unmodified}.The default is that these warnings are not given. Note that this warning is not included in -gnatwa, it must be activated explicitly. @item -gnatw.W @emph{Suppress warnings on unnecessary Warnings Off pragmas} @cindex @option{-gnatw.W} (@command{gcc}) This switch suppresses warnings for use of @code{pragma Warnings (Off, entity}. @item -gnatwx @emph{Activate warnings on Export/Import pragmas.} @cindex @option{-gnatwx} (@command{gcc}) @cindex Export/Import pragma warnings This switch activates warnings on Export/Import pragmas when the compiler detects a possible conflict between the Ada and foreign language calling sequences. For example, the use of default parameters in a convention C procedure is dubious because the C compiler cannot supply the proper default, so a warning is issued. The default is that such warnings are generated. This warning can also be turned on using @option{-gnatwa}. @item -gnatwX @emph{Suppress warnings on Export/Import pragmas.} @cindex @option{-gnatwX} (@command{gcc}) This switch suppresses warnings on Export/Import pragmas. The sense of this is that you are telling the compiler that you know what you are doing in writing the pragma, and it should not complain at you. @item -gnatw.x @emph{Activate warnings for No_Exception_Propagation mode.} @cindex @option{-gnatwm} (@command{gcc}) This switch activates warnings for exception usage when pragma Restrictions (No_Exception_Propagation) is in effect. Warnings are given for implicit or explicit exception raises which are not covered by a local handler, and for exception handlers which do not cover a local raise. The default is that these warnings are not given. @item -gnatw.X @emph{Disable warnings for No_Exception_Propagation mode.} This switch disables warnings for exception usage when pragma Restrictions (No_Exception_Propagation) is in effect. @item -gnatwy @emph{Activate warnings for Ada 2005 compatibility issues.} @cindex @option{-gnatwy} (@command{gcc}) @cindex Ada 2005 compatibility issues warnings For the most part Ada 2005 is upwards compatible with Ada 95, but there are some exceptions (for example the fact that @code{interface} is now a reserved word in Ada 2005). This switch activates several warnings to help in identifying and correcting such incompatibilities. The default is that these warnings are generated. Note that at one point Ada 2005 was called Ada 0Y, hence the choice of character. This warning can also be turned on using @option{-gnatwa}. @item -gnatwY @emph{Disable warnings for Ada 2005 compatibility issues.} @cindex @option{-gnatwY} (@command{gcc}) @cindex Ada 2005 compatibility issues warnings This switch suppresses several warnings intended to help in identifying incompatibilities between Ada 95 and Ada 2005. @item -gnatwz @emph{Activate warnings on unchecked conversions.} @cindex @option{-gnatwz} (@command{gcc}) @cindex Unchecked_Conversion warnings This switch activates warnings for unchecked conversions where the types are known at compile time to have different sizes. The default is that such warnings are generated. Warnings are also generated for subprogram pointers with different conventions, and, on VMS only, for data pointers with different conventions. This warning can also be turned on using @option{-gnatwa}. @item -gnatwZ @emph{Suppress warnings on unchecked conversions.} @cindex @option{-gnatwZ} (@command{gcc}) This switch suppresses warnings for unchecked conversions where the types are known at compile time to have different sizes or conventions. @item ^-Wunused^WARNINGS=UNUSED^ @cindex @option{-Wunused} The warnings controlled by the @option{-gnatw} switch are generated by the front end of the compiler. The @option{GCC} back end can provide additional warnings and they are controlled by the @option{-W} switch. For example, @option{^-Wunused^WARNINGS=UNUSED^} activates back end warnings for entities that are declared but not referenced. @item ^-Wuninitialized^WARNINGS=UNINITIALIZED^ @cindex @option{-Wuninitialized} Similarly, @option{^-Wuninitialized^WARNINGS=UNINITIALIZED^} activates the back end warning for uninitialized variables. This switch must be used in conjunction with an optimization level greater than zero. @item ^-Wall^/ALL_BACK_END_WARNINGS^ @cindex @option{-Wall} This switch enables all the above warnings from the @option{GCC} back end. The code generator detects a number of warning situations that are missed by the @option{GNAT} front end, and this switch can be used to activate them. The use of this switch also sets the default front end warning mode to @option{-gnatwa}, that is, most front end warnings activated as well. @item ^-w^/NO_BACK_END_WARNINGS^ @cindex @option{-w} Conversely, this switch suppresses warnings from the @option{GCC} back end. The use of this switch also sets the default front end warning mode to @option{-gnatws}, that is, front end warnings suppressed as well. @end table @noindent @ifclear vms A string of warning parameters can be used in the same parameter. For example: @smallexample -gnatwaLe @end smallexample @noindent will turn on all optional warnings except for elaboration pragma warnings, and also specify that warnings should be treated as errors. @end ifclear When no switch @option{^-gnatw^/WARNINGS^} is used, this is equivalent to: @table @option @c !sort! @item -gnatwC @item -gnatwD @item -gnatwF @item -gnatwg @item -gnatwH @item -gnatwi @item -gnatwJ @item -gnatwK @item -gnatwL @item -gnatwM @item -gnatwn @item -gnatwo @item -gnatwP @item -gnatwR @item -gnatwU @item -gnatwv @item -gnatwz @item -gnatwx @end table @node Debugging and Assertion Control @subsection Debugging and Assertion Control @table @option @item -gnata @cindex @option{-gnata} (@command{gcc}) @findex Assert @findex Debug @cindex Assertions @noindent The pragmas @code{Assert} and @code{Debug} normally have no effect and are ignored. This switch, where @samp{a} stands for assert, causes @code{Assert} and @code{Debug} pragmas to be activated. The pragmas have the form: @smallexample @cartouche @b{pragma} Assert (@var{Boolean-expression} @r{[}, @var{static-string-expression}@r{]}) @b{pragma} Debug (@var{procedure call}) @end cartouche @end smallexample @noindent The @code{Assert} pragma causes @var{Boolean-expression} to be tested. If the result is @code{True}, the pragma has no effect (other than possible side effects from evaluating the expression). If the result is @code{False}, the exception @code{Assert_Failure} declared in the package @code{System.Assertions} is raised (passing @var{static-string-expression}, if present, as the message associated with the exception). If no string expression is given the default is a string giving the file name and line number of the pragma. The @code{Debug} pragma causes @var{procedure} to be called. Note that @code{pragma Debug} may appear within a declaration sequence, allowing debugging procedures to be called between declarations. @ifset vms @item /DEBUG@r{[}=debug-level@r{]} @itemx /NODEBUG Specifies how much debugging information is to be included in the resulting object file where 'debug-level' is one of the following: @table @code @item TRACEBACK Include both debugger symbol records and traceback the object file. This is the default setting. @item ALL Include both debugger symbol records and traceback in object file. @item NONE Excludes both debugger symbol records and traceback the object file. Same as /NODEBUG. @item SYMBOLS Includes only debugger symbol records in the object file. Note that this doesn't include traceback information. @end table @end ifset @end table @node Validity Checking @subsection Validity Checking @findex Validity Checking @noindent The Ada Reference Manual defines the concept of invalid values (see RM 13.9.1). The primary source of invalid values is uninitialized variables. A scalar variable that is left uninitialized may contain an invalid value; the concept of invalid does not apply to access or composite types. It is an error to read an invalid value, but the RM does not require run-time checks to detect such errors, except for some minimal checking to prevent erroneous execution (i.e. unpredictable behavior). This corresponds to the @option{-gnatVd} switch below, which is the default. For example, by default, if the expression of a case statement is invalid, it will raise Constraint_Error rather than causing a wild jump, and if an array index on the left-hand side of an assignment is invalid, it will raise Constraint_Error rather than overwriting an arbitrary memory location. The @option{-gnatVa} may be used to enable additional validity checks, which are not required by the RM. These checks are often very expensive (which is why the RM does not require them). These checks are useful in tracking down uninitialized variables, but they are not usually recommended for production builds. The other @option{-gnatV^@var{x}^^} switches below allow finer-grained control; you can enable whichever validity checks you desire. However, for most debugging purposes, @option{-gnatVa} is sufficient, and the default @option{-gnatVd} (i.e. standard Ada behavior) is usually sufficient for non-debugging use. The @option{-gnatB} switch tells the compiler to assume that all values are valid (that is, within their declared subtype range) except in the context of a use of the Valid attribute. This means the compiler can generate more efficient code, since the range of values is better known at compile time. However, an uninitialized variable can cause wild jumps and memory corruption in this mode. The @option{-gnatV^@var{x}^^} switch allows control over the validity checking mode as described below. @ifclear vms The @code{x} argument is a string of letters that indicate validity checks that are performed or not performed in addition to the default checks required by Ada as described above. @end ifclear @ifset vms The options allowed for this qualifier indicate validity checks that are performed or not performed in addition to the default checks required by Ada as described above. @end ifset @table @option @c !sort! @item -gnatVa @emph{All validity checks.} @cindex @option{-gnatVa} (@command{gcc}) All validity checks are turned on. @ifclear vms That is, @option{-gnatVa} is equivalent to @option{gnatVcdfimorst}. @end ifclear @item -gnatVc @emph{Validity checks for copies.} @cindex @option{-gnatVc} (@command{gcc}) The right hand side of assignments, and the initializing values of object declarations are validity checked. @item -gnatVd @emph{Default (RM) validity checks.} @cindex @option{-gnatVd} (@command{gcc}) Some validity checks are done by default following normal Ada semantics (RM 13.9.1 (9-11)). A check is done in case statements that the expression is within the range of the subtype. If it is not, Constraint_Error is raised. For assignments to array components, a check is done that the expression used as index is within the range. If it is not, Constraint_Error is raised. Both these validity checks may be turned off using switch @option{-gnatVD}. They are turned on by default. If @option{-gnatVD} is specified, a subsequent switch @option{-gnatVd} will leave the checks turned on. Switch @option{-gnatVD} should be used only if you are sure that all such expressions have valid values. If you use this switch and invalid values are present, then the program is erroneous, and wild jumps or memory overwriting may occur. @item -gnatVe @emph{Validity checks for elementary components.} @cindex @option{-gnatVe} (@command{gcc}) In the absence of this switch, assignments to record or array components are not validity checked, even if validity checks for assignments generally (@option{-gnatVc}) are turned on. In Ada, assignment of composite values do not require valid data, but assignment of individual components does. So for example, there is a difference between copying the elements of an array with a slice assignment, compared to assigning element by element in a loop. This switch allows you to turn off validity checking for components, even when they are assigned component by component. @item -gnatVf @emph{Validity checks for floating-point values.} @cindex @option{-gnatVf} (@command{gcc}) In the absence of this switch, validity checking occurs only for discrete values. If @option{-gnatVf} is specified, then validity checking also applies for floating-point values, and NaNs and infinities are considered invalid, as well as out of range values for constrained types. Note that this means that standard IEEE infinity mode is not allowed. The exact contexts in which floating-point values are checked depends on the setting of other options. For example, @option{^-gnatVif^VALIDITY_CHECKING=(IN_PARAMS,FLOATS)^} or @option{^-gnatVfi^VALIDITY_CHECKING=(FLOATS,IN_PARAMS)^} (the order does not matter) specifies that floating-point parameters of mode @code{in} should be validity checked. @item -gnatVi @emph{Validity checks for @code{in} mode parameters} @cindex @option{-gnatVi} (@command{gcc}) Arguments for parameters of mode @code{in} are validity checked in function and procedure calls at the point of call. @item -gnatVm @emph{Validity checks for @code{in out} mode parameters.} @cindex @option{-gnatVm} (@command{gcc}) Arguments for parameters of mode @code{in out} are validity checked in procedure calls at the point of call. The @code{'m'} here stands for modify, since this concerns parameters that can be modified by the call. Note that there is no specific option to test @code{out} parameters, but any reference within the subprogram will be tested in the usual manner, and if an invalid value is copied back, any reference to it will be subject to validity checking. @item -gnatVn @emph{No validity checks.} @cindex @option{-gnatVn} (@command{gcc}) This switch turns off all validity checking, including the default checking for case statements and left hand side subscripts. Note that the use of the switch @option{-gnatp} suppresses all run-time checks, including validity checks, and thus implies @option{-gnatVn}. When this switch is used, it cancels any other @option{-gnatV} previously issued. @item -gnatVo @emph{Validity checks for operator and attribute operands.} @cindex @option{-gnatVo} (@command{gcc}) Arguments for predefined operators and attributes are validity checked. This includes all operators in package @code{Standard}, the shift operators defined as intrinsic in package @code{Interfaces} and operands for attributes such as @code{Pos}. Checks are also made on individual component values for composite comparisons, and on the expressions in type conversions and qualified expressions. Checks are also made on explicit ranges using @samp{..} (e.g.@: slices, loops etc). @item -gnatVp @emph{Validity checks for parameters.} @cindex @option{-gnatVp} (@command{gcc}) This controls the treatment of parameters within a subprogram (as opposed to @option{-gnatVi} and @option{-gnatVm} which control validity testing of parameters on a call. If either of these call options is used, then normally an assumption is made within a subprogram that the input arguments have been validity checking at the point of call, and do not need checking again within a subprogram). If @option{-gnatVp} is set, then this assumption is not made, and parameters are not assumed to be valid, so their validity will be checked (or rechecked) within the subprogram. @item -gnatVr @emph{Validity checks for function returns.} @cindex @option{-gnatVr} (@command{gcc}) The expression in @code{return} statements in functions is validity checked. @item -gnatVs @emph{Validity checks for subscripts.} @cindex @option{-gnatVs} (@command{gcc}) All subscripts expressions are checked for validity, whether they appear on the right side or left side (in default mode only left side subscripts are validity checked). @item -gnatVt @emph{Validity checks for tests.} @cindex @option{-gnatVt} (@command{gcc}) Expressions used as conditions in @code{if}, @code{while} or @code{exit} statements are checked, as well as guard expressions in entry calls. @end table @noindent The @option{-gnatV} switch may be followed by ^a string of letters^a list of options^ to turn on a series of validity checking options. For example, @option{^-gnatVcr^/VALIDITY_CHECKING=(COPIES, RETURNS)^} specifies that in addition to the default validity checking, copies and function return expressions are to be validity checked. In order to make it easier to specify the desired combination of effects, @ifclear vms the upper case letters @code{CDFIMORST} may be used to turn off the corresponding lower case option. @end ifclear @ifset vms the prefix @code{NO} on an option turns off the corresponding validity checking: @itemize @bullet @item @code{NOCOPIES} @item @code{NODEFAULT} @item @code{NOFLOATS} @item @code{NOIN_PARAMS} @item @code{NOMOD_PARAMS} @item @code{NOOPERANDS} @item @code{NORETURNS} @item @code{NOSUBSCRIPTS} @item @code{NOTESTS} @end itemize @end ifset Thus @option{^-gnatVaM^/VALIDITY_CHECKING=(ALL, NOMOD_PARAMS)^} turns on all validity checking options except for checking of @code{@b{in out}} procedure arguments. The specification of additional validity checking generates extra code (and in the case of @option{-gnatVa} the code expansion can be substantial). However, these additional checks can be very useful in detecting uninitialized variables, incorrect use of unchecked conversion, and other errors leading to invalid values. The use of pragma @code{Initialize_Scalars} is useful in conjunction with the extra validity checking, since this ensures that wherever possible uninitialized variables have invalid values. See also the pragma @code{Validity_Checks} which allows modification of the validity checking mode at the program source level, and also allows for temporary disabling of validity checks. @node Style Checking @subsection Style Checking @findex Style checking @noindent The @option{-gnaty^x^(option,option,@dots{})^} switch @cindex @option{-gnaty} (@command{gcc}) causes the compiler to enforce specified style rules. A limited set of style rules has been used in writing the GNAT sources themselves. This switch allows user programs to activate all or some of these checks. If the source program fails a specified style check, an appropriate message is given, preceded by the character sequence ``(style)''. This message does not prevent successful compilation (unless the @option{-gnatwe} switch is used). Note that this is by no means intended to be a general facility for checking arbitrary coding standards. It is simply an embedding of the style rules we have chosen for the GNAT sources. If you are starting a project which does not have established style standards, you may find it useful to adopt the entire set of GNAT coding standards, or some subset of them. If you already have an established set of coding standards, then it may be that selected style checking options do indeed correspond to choices you have made, but for general checking of an existing set of coding rules, you should look to the gnatcheck tool, which is designed for that purpose. @ifset vms @code{(option,option,@dots{})} is a sequence of keywords @end ifset @ifclear vms The string @var{x} is a sequence of letters or digits @end ifclear indicating the particular style checks to be performed. The following checks are defined: @table @option @c !sort! @item 0-9 @emph{Specify indentation level.} If a digit from 1-9 appears ^in the string after @option{-gnaty}^as an option for /STYLE_CHECKS^ then proper indentation is checked, with the digit indicating the indentation level required. A value of zero turns off this style check. The general style of required indentation is as specified by the examples in the Ada Reference Manual. Full line comments must be aligned with the @code{--} starting on a column that is a multiple of the alignment level, or they may be aligned the same way as the following non-blank line (this is useful when full line comments appear in the middle of a statement. @item ^a^ATTRIBUTE^ @emph{Check attribute casing.} Attribute names, including the case of keywords such as @code{digits} used as attributes names, must be written in mixed case, that is, the initial letter and any letter following an underscore must be uppercase. All other letters must be lowercase. @item ^A^ARRAY_INDEXES^ @emph{Use of array index numbers in array attributes.} When using the array attributes First, Last, Range, or Length, the index number must be omitted for one-dimensional arrays and is required for multi-dimensional arrays. @item ^b^BLANKS^ @emph{Blanks not allowed at statement end.} Trailing blanks are not allowed at the end of statements. The purpose of this rule, together with h (no horizontal tabs), is to enforce a canonical format for the use of blanks to separate source tokens. @item ^B^BOOLEAN_OPERATORS^ @emph{Check Boolean operators.} The use of AND/OR operators is not permitted except in the cases of modular operands, array operands, and simple stand-alone boolean variables or boolean constants. In all other cases AND THEN/OR ELSE are required. @item ^c^COMMENTS^ @emph{Check comments.} Comments must meet the following set of rules: @itemize @bullet @item The ``@code{--}'' that starts the column must either start in column one, or else at least one blank must precede this sequence. @item Comments that follow other tokens on a line must have at least one blank following the ``@code{--}'' at the start of the comment. @item Full line comments must have at least two blanks following the ``@code{--}'' that starts the comment, with the following exceptions. @item A line consisting only of the ``@code{--}'' characters, possibly preceded by blanks is permitted. @item A comment starting with ``@code{--x}'' where @code{x} is a special character is permitted. This allows proper processing of the output generated by specialized tools including @command{gnatprep} (where ``@code{--!}'' is used) and the SPARK annotation language (where ``@code{--#}'' is used). For the purposes of this rule, a special character is defined as being in one of the ASCII ranges @code{16#21#@dots{}16#2F#} or @code{16#3A#@dots{}16#3F#}. Note that this usage is not permitted in GNAT implementation units (i.e., when @option{-gnatg} is used). @item A line consisting entirely of minus signs, possibly preceded by blanks, is permitted. This allows the construction of box comments where lines of minus signs are used to form the top and bottom of the box. @item A comment that starts and ends with ``@code{--}'' is permitted as long as at least one blank follows the initial ``@code{--}''. Together with the preceding rule, this allows the construction of box comments, as shown in the following example: @smallexample --------------------------- -- This is a box comment -- -- with two text lines. -- --------------------------- @end smallexample @end itemize @item ^d^DOS_LINE_ENDINGS^ @emph{Check no DOS line terminators present.} All lines must be terminated by a single ASCII.LF character (in particular the DOS line terminator sequence CR/LF is not allowed). @item ^e^END^ @emph{Check end/exit labels.} Optional labels on @code{end} statements ending subprograms and on @code{exit} statements exiting named loops, are required to be present. @item ^f^VTABS^ @emph{No form feeds or vertical tabs.} Neither form feeds nor vertical tab characters are permitted in the source text. @item ^g^GNAT^ @emph{GNAT style mode} The set of style check switches is set to match that used by the GNAT sources. This may be useful when developing code that is eventually intended to be incorporated into GNAT. For further details, see GNAT sources. @item ^h^HTABS^ @emph{No horizontal tabs.} Horizontal tab characters are not permitted in the source text. Together with the b (no blanks at end of line) check, this enforces a canonical form for the use of blanks to separate source tokens. @item ^i^IF_THEN^ @emph{Check if-then layout.} The keyword @code{then} must appear either on the same line as corresponding @code{if}, or on a line on its own, lined up under the @code{if} with at least one non-blank line in between containing all or part of the condition to be tested. @item ^I^IN_MODE^ @emph{check mode IN keywords} Mode @code{in} (the default mode) is not allowed to be given explicitly. @code{in out} is fine, but not @code{in} on its own. @item ^k^KEYWORD^ @emph{Check keyword casing.} All keywords must be in lower case (with the exception of keywords such as @code{digits} used as attribute names to which this check does not apply). @item ^l^LAYOUT^ @emph{Check layout.} Layout of statement and declaration constructs must follow the recommendations in the Ada Reference Manual, as indicated by the form of the syntax rules. For example an @code{else} keyword must be lined up with the corresponding @code{if} keyword. There are two respects in which the style rule enforced by this check option are more liberal than those in the Ada Reference Manual. First in the case of record declarations, it is permissible to put the @code{record} keyword on the same line as the @code{type} keyword, and then the @code{end} in @code{end record} must line up under @code{type}. This is also permitted when the type declaration is split on two lines. For example, any of the following three layouts is acceptable: @smallexample @c ada @cartouche type q is record a : integer; b : integer; end record; type q is record a : integer; b : integer; end record; type q is record a : integer; b : integer; end record; @end cartouche @end smallexample @noindent Second, in the case of a block statement, a permitted alternative is to put the block label on the same line as the @code{declare} or @code{begin} keyword, and then line the @code{end} keyword up under the block label. For example both the following are permitted: @smallexample @c ada @cartouche Block : declare A : Integer := 3; begin Proc (A, A); end Block; Block : declare A : Integer := 3; begin Proc (A, A); end Block; @end cartouche @end smallexample @noindent The same alternative format is allowed for loops. For example, both of the following are permitted: @smallexample @c ada @cartouche Clear : while J < 10 loop A (J) := 0; end loop Clear; Clear : while J < 10 loop A (J) := 0; end loop Clear; @end cartouche @end smallexample @item ^Lnnn^MAX_NESTING=nnn^ @emph{Set maximum nesting level} The maximum level of nesting of constructs (including subprograms, loops, blocks, packages, and conditionals) may not exceed the given value @option{nnn}. A value of zero disconnects this style check. @item ^m^LINE_LENGTH^ @emph{Check maximum line length.} The length of source lines must not exceed 79 characters, including any trailing blanks. The value of 79 allows convenient display on an 80 character wide device or window, allowing for possible special treatment of 80 character lines. Note that this count is of characters in the source text. This means that a tab character counts as one character in this count but a wide character sequence counts as a single character (however many bytes are needed in the encoding). @item ^Mnnn^MAX_LENGTH=nnn^ @emph{Set maximum line length.} The length of lines must not exceed the given value @option{nnn}. The maximum value that can be specified is 32767. @item ^n^STANDARD_CASING^ @emph{Check casing of entities in Standard.} Any identifier from Standard must be cased to match the presentation in the Ada Reference Manual (for example, @code{Integer} and @code{ASCII.NUL}). @item ^N^NONE^ @emph{Turn off all style checks} All style check options are turned off. @item ^o^ORDERED_SUBPROGRAMS^ @emph{Check order of subprogram bodies.} All subprogram bodies in a given scope (e.g.@: a package body) must be in alphabetical order. The ordering rule uses normal Ada rules for comparing strings, ignoring casing of letters, except that if there is a trailing numeric suffix, then the value of this suffix is used in the ordering (e.g.@: Junk2 comes before Junk10). @item ^O^OVERRIDING_INDICATORS^ @emph{Check that overriding subprograms are explicitly marked as such.} The declaration of a primitive operation of a type extension that overrides an inherited operation must carry an overriding indicator. @item ^p^PRAGMA^ @emph{Check pragma casing.} Pragma names must be written in mixed case, that is, the initial letter and any letter following an underscore must be uppercase. All other letters must be lowercase. @item ^r^REFERENCES^ @emph{Check references.} All identifier references must be cased in the same way as the corresponding declaration. No specific casing style is imposed on identifiers. The only requirement is for consistency of references with declarations. @item ^S^STATEMENTS_AFTER_THEN_ELSE^ @emph{Check no statements after THEN/ELSE.} No statements are allowed on the same line as a THEN or ELSE keyword following the keyword in an IF statement. OR ELSE and AND THEN are not affected, and a special exception allows a pragma to appear after ELSE. @item ^s^SPECS^ @emph{Check separate specs.} Separate declarations (``specs'') are required for subprograms (a body is not allowed to serve as its own declaration). The only exception is that parameterless library level procedures are not required to have a separate declaration. This exception covers the most frequent form of main program procedures. @item ^t^TOKEN^ @emph{Check token spacing.} The following token spacing rules are enforced: @itemize @bullet @item The keywords @code{@b{abs}} and @code{@b{not}} must be followed by a space. @item The token @code{=>} must be surrounded by spaces. @item The token @code{<>} must be preceded by a space or a left parenthesis. @item Binary operators other than @code{**} must be surrounded by spaces. There is no restriction on the layout of the @code{**} binary operator. @item Colon must be surrounded by spaces. @item Colon-equal (assignment, initialization) must be surrounded by spaces. @item Comma must be the first non-blank character on the line, or be immediately preceded by a non-blank character, and must be followed by a space. @item If the token preceding a left parenthesis ends with a letter or digit, then a space must separate the two tokens. @item if the token following a right parenthesis starts with a letter or digit, then a space must separate the two tokens. @item A right parenthesis must either be the first non-blank character on a line, or it must be preceded by a non-blank character. @item A semicolon must not be preceded by a space, and must not be followed by a non-blank character. @item A unary plus or minus may not be followed by a space. @item A vertical bar must be surrounded by spaces. @end itemize @item ^u^UNNECESSARY_BLANK_LINES^ @emph{Check unnecessary blank lines.} Unnecessary blank lines are not allowed. A blank line is considered unnecessary if it appears at the end of the file, or if more than one blank line occurs in sequence. @item ^x^XTRA_PARENS^ @emph{Check extra parentheses.} Unnecessary extra level of parentheses (C-style) are not allowed around conditions in @code{if} statements, @code{while} statements and @code{exit} statements. @item ^y^ALL_BUILTIN^ @emph{Set all standard style check options} This is equivalent to @code{gnaty3aAbcefhiklmnprst}, that is all checking options enabled with the exception of @option{-gnatyo}, @option{-gnatyI}, @option{-gnatyS}, @option{-gnatyLnnn}, @option{-gnatyd}, @option{-gnatyu}, and @option{-gnatyx}. @ifclear vms @item - @emph{Remove style check options} This causes any subsequent options in the string to act as canceling the corresponding style check option. To cancel maximum nesting level control, use @option{L} parameter witout any integer value after that, because any digit following @option{-} in the parameter string of the @option{-gnaty} option will be threated as canceling indentation check. The same is true for @option{M} parameter. @option{y} and @option{N} parameters are not allowed after @option{-}. @item + This causes any subsequent options in the string to enable the corresponding style check option. That is, it cancels the effect of a previous ^-^REMOVE^, if any. @end ifclear @ifset vms @item NOxxx @emph{Removing style check options} If the name of a style check is preceded by @option{NO} then the corresponding style check is turned off. For example @option{NOCOMMENTS} turns off style checking for comments. @end ifset @end table @noindent In the above rules, appearing in column one is always permitted, that is, counts as meeting either a requirement for a required preceding space, or as meeting a requirement for no preceding space. Appearing at the end of a line is also always permitted, that is, counts as meeting either a requirement for a following space, or as meeting a requirement for no following space. @noindent If any of these style rules is violated, a message is generated giving details on the violation. The initial characters of such messages are always ``@code{(style)}''. Note that these messages are treated as warning messages, so they normally do not prevent the generation of an object file. The @option{-gnatwe} switch can be used to treat warning messages, including style messages, as fatal errors. The switch @ifclear vms @option{-gnaty} on its own (that is not followed by any letters or digits), then the effect is equivalent to the use of @option{-gnatyy}, as described above, that is all built-in standard style check options are enabled. @end ifclear @ifset vms /STYLE_CHECKS=ALL_BUILTIN enables all checking options with the exception of ORDERED_SUBPROGRAMS, UNNECESSARY_BLANK_LINES, XTRA_PARENS, and DOS_LINE_ENDINGS. In addition @end ifset The switch @ifclear vms @option{-gnatyN} @end ifclear @ifset vms /STYLE_CHECKS=NONE @end ifset clears any previously set style checks. @node Run-Time Checks @subsection Run-Time Checks @cindex Division by zero @cindex Access before elaboration @cindex Checks, division by zero @cindex Checks, access before elaboration @cindex Checks, stack overflow checking @noindent By default, the following checks are suppressed: integer overflow checks, stack overflow checks, and checks for access before elaboration on subprogram calls. All other checks, including range checks and array bounds checks, are turned on by default. The following @command{gcc} switches refine this default behavior. @table @option @c !sort! @item -gnatp @cindex @option{-gnatp} (@command{gcc}) @cindex Suppressing checks @cindex Checks, suppressing @findex Suppress This switch causes the unit to be compiled as though @code{pragma Suppress (All_checks)} had been present in the source. Validity checks are also eliminated (in other words @option{-gnatp} also implies @option{-gnatVn}. Use this switch to improve the performance of the code at the expense of safety in the presence of invalid data or program bugs. Note that when checks are suppressed, the compiler is allowed, but not required, to omit the checking code. If the run-time cost of the checking code is zero or near-zero, the compiler will generate it even if checks are suppressed. In particular, if the compiler can prove that a certain check will necessarily fail, it will generate code to do an unconditional ``raise'', even if checks are suppressed. The compiler warns in this case. Another case in which checks may not be eliminated is when they are embedded in certain run time routines such as math library routines. Of course, run-time checks are omitted whenever the compiler can prove that they will not fail, whether or not checks are suppressed. Note that if you suppress a check that would have failed, program execution is erroneous, which means the behavior is totally unpredictable. The program might crash, or print wrong answers, or do anything else. It might even do exactly what you wanted it to do (and then it might start failing mysteriously next week or next year). The compiler will generate code based on the assumption that the condition being checked is true, which can result in disaster if that assumption is wrong. The @option{-gnatp} switch has no effect if a subsequent @option{-gnat-p} switch appears. @item -gnat-p @cindex @option{-gnat-p} (@command{gcc}) @cindex Suppressing checks @cindex Checks, suppressing @findex Suppress This switch cancels the effect of a previous @option{gnatp} switch. @item -gnato @cindex @option{-gnato} (@command{gcc}) @cindex Overflow checks @cindex Check, overflow Enables overflow checking for integer operations. This causes GNAT to generate slower and larger executable programs by adding code to check for overflow (resulting in raising @code{Constraint_Error} as required by standard Ada semantics). These overflow checks correspond to situations in which the true value of the result of an operation may be outside the base range of the result type. The following example shows the distinction: @smallexample @c ada X1 : Integer := "Integer'Last"; X2 : Integer range 1 .. 5 := "5"; X3 : Integer := "Integer'Last"; X4 : Integer range 1 .. 5 := "5"; F : Float := "2.0E+20"; @dots{} X1 := X1 + 1; X2 := X2 + 1; X3 := Integer (F); X4 := Integer (F); @end smallexample @noindent Note that if explicit values are assigned at compile time, the compiler may be able to detect overflow at compile time, in which case no actual run-time checking code is required, and Constraint_Error will be raised unconditionally, with or without @option{-gnato}. That's why the assigned values in the above fragment are in quotes, the meaning is "assign a value not known to the compiler that happens to be equal to ...". The remaining discussion assumes that the compiler cannot detect the values at compile time. Here the first addition results in a value that is outside the base range of Integer, and hence requires an overflow check for detection of the constraint error. Thus the first assignment to @code{X1} raises a @code{Constraint_Error} exception only if @option{-gnato} is set. The second increment operation results in a violation of the explicit range constraint; such range checks are performed by default, and are unaffected by @option{-gnato}. The two conversions of @code{F} both result in values that are outside the base range of type @code{Integer} and thus will raise @code{Constraint_Error} exceptions only if @option{-gnato} is used. The fact that the result of the second conversion is assigned to variable @code{X4} with a restricted range is irrelevant, since the problem is in the conversion, not the assignment. Basically the rule is that in the default mode (@option{-gnato} not used), the generated code assures that all integer variables stay within their declared ranges, or within the base range if there is no declared range. This prevents any serious problems like indexes out of range for array operations. What is not checked in default mode is an overflow that results in an in-range, but incorrect value. In the above example, the assignments to @code{X1}, @code{X2}, @code{X3} all give results that are within the range of the target variable, but the result is wrong in the sense that it is too large to be represented correctly. Typically the assignment to @code{X1} will result in wrap around to the largest negative number. The conversions of @code{F} will result in some @code{Integer} value and if that integer value is out of the @code{X4} range then the subsequent assignment would generate an exception. @findex Machine_Overflows Note that the @option{-gnato} switch does not affect the code generated for any floating-point operations; it applies only to integer semantics). For floating-point, GNAT has the @code{Machine_Overflows} attribute set to @code{False} and the normal mode of operation is to generate IEEE NaN and infinite values on overflow or invalid operations (such as dividing 0.0 by 0.0). The reason that we distinguish overflow checking from other kinds of range constraint checking is that a failure of an overflow check, unlike for example the failure of a range check, can result in an incorrect value, but cannot cause random memory destruction (like an out of range subscript), or a wild jump (from an out of range case value). Overflow checking is also quite expensive in time and space, since in general it requires the use of double length arithmetic. Note again that @option{-gnato} is off by default, so overflow checking is not performed in default mode. This means that out of the box, with the default settings, GNAT does not do all the checks expected from the language description in the Ada Reference Manual. If you want all constraint checks to be performed, as described in this Manual, then you must explicitly use the -gnato switch either on the @command{gnatmake} or @command{gcc} command. @item -gnatE @cindex @option{-gnatE} (@command{gcc}) @cindex Elaboration checks @cindex Check, elaboration Enables dynamic checks for access-before-elaboration on subprogram calls and generic instantiations. Note that @option{-gnatE} is not necessary for safety, because in the default mode, GNAT ensures statically that the checks would not fail. For full details of the effect and use of this switch, @xref{Compiling Using gcc}. @item -fstack-check @cindex @option{-fstack-check} (@command{gcc}) @cindex Stack Overflow Checking @cindex Checks, stack overflow checking Activates stack overflow checking. For full details of the effect and use of this switch see @ref{Stack Overflow Checking}. @end table @findex Unsuppress @noindent The setting of these switches only controls the default setting of the checks. You may modify them using either @code{Suppress} (to remove checks) or @code{Unsuppress} (to add back suppressed checks) pragmas in the program source. @node Using gcc for Syntax Checking @subsection Using @command{gcc} for Syntax Checking @table @option @item -gnats @cindex @option{-gnats} (@command{gcc}) @ifclear vms @noindent The @code{s} stands for ``syntax''. @end ifclear Run GNAT in syntax checking only mode. For example, the command @smallexample $ gcc -c -gnats x.adb @end smallexample @noindent compiles file @file{x.adb} in syntax-check-only mode. You can check a series of files in a single command @ifclear vms , and can use wild cards to specify such a group of files. Note that you must specify the @option{-c} (compile only) flag in addition to the @option{-gnats} flag. @end ifclear . You may use other switches in conjunction with @option{-gnats}. In particular, @option{-gnatl} and @option{-gnatv} are useful to control the format of any generated error messages. When the source file is empty or contains only empty lines and/or comments, the output is a warning: @smallexample $ gcc -c -gnats -x ada toto.txt toto.txt:1:01: warning: empty file, contains no compilation units $ @end smallexample Otherwise, the output is simply the error messages, if any. No object file or ALI file is generated by a syntax-only compilation. Also, no units other than the one specified are accessed. For example, if a unit @code{X} @code{with}'s a unit @code{Y}, compiling unit @code{X} in syntax check only mode does not access the source file containing unit @code{Y}. @cindex Multiple units, syntax checking Normally, GNAT allows only a single unit in a source file. However, this restriction does not apply in syntax-check-only mode, and it is possible to check a file containing multiple compilation units concatenated together. This is primarily used by the @code{gnatchop} utility (@pxref{Renaming Files Using gnatchop}). @end table @node Using gcc for Semantic Checking @subsection Using @command{gcc} for Semantic Checking @table @option @item -gnatc @cindex @option{-gnatc} (@command{gcc}) @ifclear vms @noindent The @code{c} stands for ``check''. @end ifclear Causes the compiler to operate in semantic check mode, with full checking for all illegalities specified in the Ada Reference Manual, but without generation of any object code (no object file is generated). Because dependent files must be accessed, you must follow the GNAT semantic restrictions on file structuring to operate in this mode: @itemize @bullet @item The needed source files must be accessible (@pxref{Search Paths and the Run-Time Library (RTL)}). @item Each file must contain only one compilation unit. @item The file name and unit name must match (@pxref{File Naming Rules}). @end itemize The output consists of error messages as appropriate. No object file is generated. An @file{ALI} file is generated for use in the context of cross-reference tools, but this file is marked as not being suitable for binding (since no object file is generated). The checking corresponds exactly to the notion of legality in the Ada Reference Manual. Any unit can be compiled in semantics-checking-only mode, including units that would not normally be compiled (subunits, and specifications where a separate body is present). @end table @node Compiling Different Versions of Ada @subsection Compiling Different Versions of Ada @noindent The switches described in this section allow you to explicitly specify the version of the Ada language that your programs are written in. By default @value{EDITION} assumes @value{DEFAULTLANGUAGEVERSION}, but you can also specify @value{NONDEFAULTLANGUAGEVERSION} or indicate Ada 83 compatibility mode. @table @option @cindex Compatibility with Ada 83 @item -gnat83 (Ada 83 Compatibility Mode) @cindex @option{-gnat83} (@command{gcc}) @cindex ACVC, Ada 83 tests @cindex Ada 83 mode @noindent Although GNAT is primarily an Ada 95 / Ada 2005 compiler, this switch specifies that the program is to be compiled in Ada 83 mode. With @option{-gnat83}, GNAT rejects most post-Ada 83 extensions and applies Ada 83 semantics where this can be done easily. It is not possible to guarantee this switch does a perfect job; some subtle tests, such as are found in earlier ACVC tests (and that have been removed from the ACATS suite for Ada 95), might not compile correctly. Nevertheless, this switch may be useful in some circumstances, for example where, due to contractual reasons, existing code needs to be maintained using only Ada 83 features. With few exceptions (most notably the need to use @code{<>} on @cindex Generic formal parameters unconstrained generic formal parameters, the use of the new Ada 95 / Ada 2005 reserved words, and the use of packages with optional bodies), it is not necessary to specify the @option{-gnat83} switch when compiling Ada 83 programs, because, with rare exceptions, Ada 95 and Ada 2005 are upwardly compatible with Ada 83. Thus a correct Ada 83 program is usually also a correct program in these later versions of the language standard. For further information, please refer to @ref{Compatibility and Porting Guide}. @item -gnat95 (Ada 95 mode) @cindex @option{-gnat95} (@command{gcc}) @cindex Ada 95 mode @noindent This switch directs the compiler to implement the Ada 95 version of the language. Since Ada 95 is almost completely upwards compatible with Ada 83, Ada 83 programs may generally be compiled using this switch (see the description of the @option{-gnat83} switch for further information about Ada 83 mode). If an Ada 2005 program is compiled in Ada 95 mode, uses of the new Ada 2005 features will cause error messages or warnings. This switch also can be used to cancel the effect of a previous @option{-gnat83}, @option{-gnat05/2005}, or @option{-gnat12/2012} switch earlier in the command line. @item -gnat05 or -gnat2005 (Ada 2005 mode) @cindex @option{-gnat05} (@command{gcc}) @cindex @option{-gnat2005} (@command{gcc}) @cindex Ada 2005 mode @noindent This switch directs the compiler to implement the Ada 2005 version of the language, as documented in the official Ada standards document. Since Ada 2005 is almost completely upwards compatible with Ada 95 (and thus also with Ada 83), Ada 83 and Ada 95 programs may generally be compiled using this switch (see the description of the @option{-gnat83} and @option{-gnat95} switches for further information). @ifset PROEDITION Note that even though Ada 2005 is the current official version of the language, GNAT still compiles in Ada 95 mode by default, so if you are using Ada 2005 features in your program, you must use this switch (or the equivalent Ada_05 or Ada_2005 configuration pragmas). @end ifset @item -gnat12 or -gnat2012 (Ada 2012 mode) @cindex @option{-gnat12} (@command{gcc}) @cindex @option{-gnat2012} (@command{gcc}) @cindex Ada 2012 mode @noindent This switch directs the compiler to implement the Ada 2012 version of the language. Since Ada 2012 is almost completely upwards compatible with Ada 2005 (and thus also with Ada 83, and Ada 95), Ada 83 and Ada 95 programs may generally be compiled using this switch (see the description of the @option{-gnat83}, @option{-gnat95}, and @option{-gnat05/2005} switches for further information). For information about the approved ``Ada Issues'' that have been incorporated into Ada 2012, see @url{http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs}. Included with GNAT releases is a file @file{features-ada12} that describes the set of implemented Ada 2012 features. @item -gnatX (Enable GNAT Extensions) @cindex @option{-gnatX} (@command{gcc}) @cindex Ada language extensions @cindex GNAT extensions @noindent This switch directs the compiler to implement the latest version of the language (currently Ada 2012) and also to enable certain GNAT implementation extensions that are not part of any Ada standard. For a full list of these extensions, see the GNAT reference manual. @end table @node Character Set Control @subsection Character Set Control @table @option @item ^-gnati^/IDENTIFIER_CHARACTER_SET=^@var{c} @cindex @option{^-gnati^/IDENTIFIER_CHARACTER_SET^} (@command{gcc}) @noindent Normally GNAT recognizes the Latin-1 character set in source program identifiers, as described in the Ada Reference Manual. This switch causes GNAT to recognize alternate character sets in identifiers. @var{c} is a single character ^^or word^ indicating the character set, as follows: @table @code @item 1 ISO 8859-1 (Latin-1) identifiers @item 2 ISO 8859-2 (Latin-2) letters allowed in identifiers @item 3 ISO 8859-3 (Latin-3) letters allowed in identifiers @item 4 ISO 8859-4 (Latin-4) letters allowed in identifiers @item 5 ISO 8859-5 (Cyrillic) letters allowed in identifiers @item 9 ISO 8859-15 (Latin-9) letters allowed in identifiers @item ^p^PC^ IBM PC letters (code page 437) allowed in identifiers @item ^8^PC850^ IBM PC letters (code page 850) allowed in identifiers @item ^f^FULL_UPPER^ Full upper-half codes allowed in identifiers @item ^n^NO_UPPER^ No upper-half codes allowed in identifiers @item ^w^WIDE^ Wide-character codes (that is, codes greater than 255) allowed in identifiers @end table @xref{Foreign Language Representation}, for full details on the implementation of these character sets. @item ^-gnatW^/WIDE_CHARACTER_ENCODING=^@var{e} @cindex @option{^-gnatW^/WIDE_CHARACTER_ENCODING^} (@command{gcc}) Specify the method of encoding for wide characters. @var{e} is one of the following: @table @code @item ^h^HEX^ Hex encoding (brackets coding also recognized) @item ^u^UPPER^ Upper half encoding (brackets encoding also recognized) @item ^s^SHIFT_JIS^ Shift/JIS encoding (brackets encoding also recognized) @item ^e^EUC^ EUC encoding (brackets encoding also recognized) @item ^8^UTF8^ UTF-8 encoding (brackets encoding also recognized) @item ^b^BRACKETS^ Brackets encoding only (default value) @end table For full details on these encoding methods see @ref{Wide Character Encodings}. Note that brackets coding is always accepted, even if one of the other options is specified, so for example @option{-gnatW8} specifies that both brackets and UTF-8 encodings will be recognized. The units that are with'ed directly or indirectly will be scanned using the specified representation scheme, and so if one of the non-brackets scheme is used, it must be used consistently throughout the program. However, since brackets encoding is always recognized, it may be conveniently used in standard libraries, allowing these libraries to be used with any of the available coding schemes. scheme. If no @option{-gnatW?} parameter is present, then the default representation is normally Brackets encoding only. However, if the first three characters of the file are 16#EF# 16#BB# 16#BF# (the standard byte order mark or BOM for UTF-8), then these three characters are skipped and the default representation for the file is set to UTF-8. Note that the wide character representation that is specified (explicitly or by default) for the main program also acts as the default encoding used for Wide_Text_IO files if not specifically overridden by a WCEM form parameter. @end table @node File Naming Control @subsection File Naming Control @table @option @item ^-gnatk^/FILE_NAME_MAX_LENGTH=^@var{n} @cindex @option{-gnatk} (@command{gcc}) Activates file name ``krunching''. @var{n}, a decimal integer in the range 1-999, indicates the maximum allowable length of a file name (not including the @file{.ads} or @file{.adb} extension). The default is not to enable file name krunching. For the source file naming rules, @xref{File Naming Rules}. @end table @node Subprogram Inlining Control @subsection Subprogram Inlining Control @table @option @c !sort! @item -gnatn @cindex @option{-gnatn} (@command{gcc}) @ifclear vms The @code{n} here is intended to suggest the first syllable of the word ``inline''. @end ifclear GNAT recognizes and processes @code{Inline} pragmas. However, for the inlining to actually occur, optimization must be enabled. To enable inlining of subprograms specified by pragma @code{Inline}, you must also specify this switch. In the absence of this switch, GNAT does not attempt inlining and does not need to access the bodies of subprograms for which @code{pragma Inline} is specified if they are not in the current unit. If you specify this switch the compiler will access these bodies, creating an extra source dependency for the resulting object file, and where possible, the call will be inlined. For further details on when inlining is possible see @ref{Inlining of Subprograms}. @item -gnatN @cindex @option{-gnatN} (@command{gcc}) This switch activates front-end inlining which also generates additional dependencies. When using a gcc-based back end (in practice this means using any version of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of @option{-gnatN} is deprecated, and the use of @option{-gnatn} is preferred. Historically front end inlining was more extensive than the gcc back end inlining, but that is no longer the case. @end table @node Auxiliary Output Control @subsection Auxiliary Output Control @table @option @item -gnatt @cindex @option{-gnatt} (@command{gcc}) @cindex Writing internal trees @cindex Internal trees, writing to file Causes GNAT to write the internal tree for a unit to a file (with the extension @file{.adt}. This not normally required, but is used by separate analysis tools. Typically these tools do the necessary compilations automatically, so you should not have to specify this switch in normal operation. Note that the combination of switches @option{-gnatct} generates a tree in the form required by ASIS applications. @item -gnatu @cindex @option{-gnatu} (@command{gcc}) Print a list of units required by this compilation on @file{stdout}. The listing includes all units on which the unit being compiled depends either directly or indirectly. @ifclear vms @item -pass-exit-codes @cindex @option{-pass-exit-codes} (@command{gcc}) If this switch is not used, the exit code returned by @command{gcc} when compiling multiple files indicates whether all source files have been successfully used to generate object files or not. When @option{-pass-exit-codes} is used, @command{gcc} exits with an extended exit status and allows an integrated development environment to better react to a compilation failure. Those exit status are: @table @asis @item 5 There was an error in at least one source file. @item 3 At least one source file did not generate an object file. @item 2 The compiler died unexpectedly (internal error for example). @item 0 An object file has been generated for every source file. @end table @end ifclear @end table @node Debugging Control @subsection Debugging Control @table @option @c !sort! @cindex Debugging options @ifclear vms @item -gnatd@var{x} @cindex @option{-gnatd} (@command{gcc}) Activate internal debugging switches. @var{x} is a letter or digit, or string of letters or digits, which specifies the type of debugging outputs desired. Normally these are used only for internal development or system debugging purposes. You can find full documentation for these switches in the body of the @code{Debug} unit in the compiler source file @file{debug.adb}. @end ifclear @item -gnatG[=nn] @cindex @option{-gnatG} (@command{gcc}) This switch causes the compiler to generate auxiliary output containing a pseudo-source listing of the generated expanded code. Like most Ada compilers, GNAT works by first transforming the high level Ada code into lower level constructs. For example, tasking operations are transformed into calls to the tasking run-time routines. A unique capability of GNAT is to list this expanded code in a form very close to normal Ada source. This is very useful in understanding the implications of various Ada usage on the efficiency of the generated code. There are many cases in Ada (e.g.@: the use of controlled types), where simple Ada statements can generate a lot of run-time code. By using @option{-gnatG} you can identify these cases, and consider whether it may be desirable to modify the coding approach to improve efficiency. The optional parameter @code{nn} if present after -gnatG specifies an alternative maximum line length that overrides the normal default of 72. This value is in the range 40-999999, values less than 40 being silently reset to 40. The equal sign is optional. The format of the output is very similar to standard Ada source, and is easily understood by an Ada programmer. The following special syntactic additions correspond to low level features used in the generated code that do not have any exact analogies in pure Ada source form. The following is a partial list of these special constructions. See the spec of package @code{Sprint} in file @file{sprint.ads} for a full list. If the switch @option{-gnatL} is used in conjunction with @cindex @option{-gnatL} (@command{gcc}) @option{-gnatG}, then the original source lines are interspersed in the expanded source (as comment lines with the original line number). @table @code @item new @var{xxx} @r{[}storage_pool = @var{yyy}@r{]} Shows the storage pool being used for an allocator. @item at end @var{procedure-name}; Shows the finalization (cleanup) procedure for a scope. @item (if @var{expr} then @var{expr} else @var{expr}) Conditional expression equivalent to the @code{x?y:z} construction in C. @item @var{target}^^^(@var{source}) A conversion with floating-point truncation instead of rounding. @item @var{target}?(@var{source}) A conversion that bypasses normal Ada semantic checking. In particular enumeration types and fixed-point types are treated simply as integers. @item @var{target}?^^^(@var{source}) Combines the above two cases. @item @var{x} #/ @var{y} @itemx @var{x} #mod @var{y} @itemx @var{x} #* @var{y} @itemx @var{x} #rem @var{y} A division or multiplication of fixed-point values which are treated as integers without any kind of scaling. @item free @var{expr} @r{[}storage_pool = @var{xxx}@r{]} Shows the storage pool associated with a @code{free} statement. @item [subtype or type declaration] Used to list an equivalent declaration for an internally generated type that is referenced elsewhere in the listing. @c @item freeze @var{type-name} @ovar{actions} @c Expanding @ovar macro inline (explanation in macro def comments) @item freeze @var{type-name} @r{[}@var{actions}@r{]} Shows the point at which @var{type-name} is frozen, with possible associated actions to be performed at the freeze point. @item reference @var{itype} Reference (and hence definition) to internal type @var{itype}. @item @var{function-name}! (@var{arg}, @var{arg}, @var{arg}) Intrinsic function call. @item @var{label-name} : label Declaration of label @var{labelname}. @item #$ @var{subprogram-name} An implicit call to a run-time support routine (to meet the requirement of H.3.1(9) in a convenient manner). @item @var{expr} && @var{expr} && @var{expr} @dots{} && @var{expr} A multiple concatenation (same effect as @var{expr} & @var{expr} & @var{expr}, but handled more efficiently). @item [constraint_error] Raise the @code{Constraint_Error} exception. @item @var{expression}'reference A pointer to the result of evaluating @var{expression}. @item @var{target-type}!(@var{source-expression}) An unchecked conversion of @var{source-expression} to @var{target-type}. @item [@var{numerator}/@var{denominator}] Used to represent internal real literals (that) have no exact representation in base 2-16 (for example, the result of compile time evaluation of the expression 1.0/27.0). @end table @item -gnatD[=nn] @cindex @option{-gnatD} (@command{gcc}) When used in conjunction with @option{-gnatG}, this switch causes the expanded source, as described above for @option{-gnatG} to be written to files with names @file{^xxx.dg^XXX_DG^}, where @file{xxx} is the normal file name, instead of to the standard output file. For example, if the source file name is @file{hello.adb}, then a file @file{^hello.adb.dg^HELLO.ADB_DG^} will be written. The debugging information generated by the @command{gcc} @option{^-g^/DEBUG^} switch will refer to the generated @file{^xxx.dg^XXX_DG^} file. This allows you to do source level debugging using the generated code which is sometimes useful for complex code, for example to find out exactly which part of a complex construction raised an exception. This switch also suppress generation of cross-reference information (see @option{-gnatx}) since otherwise the cross-reference information would refer to the @file{^.dg^.DG^} file, which would cause confusion since this is not the original source file. Note that @option{-gnatD} actually implies @option{-gnatG} automatically, so it is not necessary to give both options. In other words @option{-gnatD} is equivalent to @option{-gnatDG}). If the switch @option{-gnatL} is used in conjunction with @cindex @option{-gnatL} (@command{gcc}) @option{-gnatDG}, then the original source lines are interspersed in the expanded source (as comment lines with the original line number). The optional parameter @code{nn} if present after -gnatD specifies an alternative maximum line length that overrides the normal default of 72. This value is in the range 40-999999, values less than 40 being silently reset to 40. The equal sign is optional. @item -gnatr @cindex @option{-gnatr} (@command{gcc}) @cindex pragma Restrictions This switch causes pragma Restrictions to be treated as Restriction_Warnings so that violation of restrictions causes warnings rather than illegalities. This is useful during the development process when new restrictions are added or investigated. The switch also causes pragma Profile to be treated as Profile_Warnings, and pragma Restricted_Run_Time and pragma Ravenscar set restriction warnings rather than restrictions. @ifclear vms @item -gnatR@r{[}0@r{|}1@r{|}2@r{|}3@r{[}s@r{]]} @cindex @option{-gnatR} (@command{gcc}) This switch controls output from the compiler of a listing showing representation information for declared types and objects. For @option{-gnatR0}, no information is output (equivalent to omitting the @option{-gnatR} switch). For @option{-gnatR1} (which is the default, so @option{-gnatR} with no parameter has the same effect), size and alignment information is listed for declared array and record types. For @option{-gnatR2}, size and alignment information is listed for all declared types and objects. Finally @option{-gnatR3} includes symbolic expressions for values that are computed at run time for variant records. These symbolic expressions have a mostly obvious format with #n being used to represent the value of the n'th discriminant. See source files @file{repinfo.ads/adb} in the @code{GNAT} sources for full details on the format of @option{-gnatR3} output. If the switch is followed by an s (e.g.@: @option{-gnatR2s}), then the output is to a file with the name @file{^file.rep^file_REP^} where file is the name of the corresponding source file. @end ifclear @ifset vms @item /REPRESENTATION_INFO @cindex @option{/REPRESENTATION_INFO} (@command{gcc}) This qualifier controls output from the compiler of a listing showing representation information for declared types and objects. For @option{/REPRESENTATION_INFO=NONE}, no information is output (equivalent to omitting the @option{/REPRESENTATION_INFO} qualifier). @option{/REPRESENTATION_INFO} without option is equivalent to @option{/REPRESENTATION_INFO=ARRAYS}. For @option{/REPRESENTATION_INFO=ARRAYS}, size and alignment information is listed for declared array and record types. For @option{/REPRESENTATION_INFO=OBJECTS}, size and alignment information is listed for all expression information for values that are computed at run time for variant records. These symbolic expressions have a mostly obvious format with #n being used to represent the value of the n'th discriminant. See source files @file{REPINFO.ADS/ADB} in the @code{GNAT} sources for full details on the format of @option{/REPRESENTATION_INFO=SYMBOLIC} output. If _FILE is added at the end of an option (e.g.@: @option{/REPRESENTATION_INFO=ARRAYS_FILE}), then the output is to a file with the name @file{file_REP} where file is the name of the corresponding source file. @end ifset Note that it is possible for record components to have zero size. In this case, the component clause uses an obvious extension of permitted Ada syntax, for example @code{at 0 range 0 .. -1}. Representation information requires that code be generated (since it is the code generator that lays out complex data structures). If an attempt is made to output representation information when no code is generated, for example when a subunit is compiled on its own, then no information can be generated and the compiler outputs a message to this effect. @item -gnatS @cindex @option{-gnatS} (@command{gcc}) The use of the switch @option{-gnatS} for an Ada compilation will cause the compiler to output a representation of package Standard in a form very close to standard Ada. It is not quite possible to do this entirely in standard Ada (since new numeric base types cannot be created in standard Ada), but the output is easily readable to any Ada programmer, and is useful to determine the characteristics of target dependent types in package Standard. @item -gnatx @cindex @option{-gnatx} (@command{gcc}) Normally the compiler generates full cross-referencing information in the @file{ALI} file. This information is used by a number of tools, including @code{gnatfind} and @code{gnatxref}. The @option{-gnatx} switch suppresses this information. This saves some space and may slightly speed up compilation, but means that these tools cannot be used. @end table @node Exception Handling Control @subsection Exception Handling Control @noindent GNAT uses two methods for handling exceptions at run-time. The @code{setjmp/longjmp} method saves the context when entering a frame with an exception handler. Then when an exception is raised, the context can be restored immediately, without the need for tracing stack frames. This method provides very fast exception propagation, but introduces significant overhead for the use of exception handlers, even if no exception is raised. The other approach is called ``zero cost'' exception handling. With this method, the compiler builds static tables to describe the exception ranges. No dynamic code is required when entering a frame containing an exception handler. When an exception is raised, the tables are used to control a back trace of the subprogram invocation stack to locate the required exception handler. This method has considerably poorer performance for the propagation of exceptions, but there is no overhead for exception handlers if no exception is raised. Note that in this mode and in the context of mixed Ada and C/C++ programming, to propagate an exception through a C/C++ code, the C/C++ code must be compiled with the @option{-funwind-tables} GCC's option. The following switches may be used to control which of the two exception handling methods is used. @table @option @c !sort! @item --RTS=sjlj @cindex @option{--RTS=sjlj} (@command{gnatmake}) This switch causes the setjmp/longjmp run-time (when available) to be used for exception handling. If the default mechanism for the target is zero cost exceptions, then this switch can be used to modify this default, and must be used for all units in the partition. This option is rarely used. One case in which it may be advantageous is if you have an application where exception raising is common and the overall performance of the application is improved by favoring exception propagation. @item --RTS=zcx @cindex @option{--RTS=zcx} (@command{gnatmake}) @cindex Zero Cost Exceptions This switch causes the zero cost approach to be used for exception handling. If this is the default mechanism for the target (see below), then this switch is unneeded. If the default mechanism for the target is setjmp/longjmp exceptions, then this switch can be used to modify this default, and must be used for all units in the partition. This option can only be used if the zero cost approach is available for the target in use, otherwise it will generate an error. @end table @noindent The same option @option{--RTS} must be used both for @command{gcc} and @command{gnatbind}. Passing this option to @command{gnatmake} (@pxref{Switches for gnatmake}) will ensure the required consistency through the compilation and binding steps. @node Units to Sources Mapping Files @subsection Units to Sources Mapping Files @table @option @item -gnatem=@var{path} @cindex @option{-gnatem} (@command{gcc}) A mapping file is a way to communicate to the compiler two mappings: from unit names to file names (without any directory information) and from file names to path names (with full directory information). These mappings are used by the compiler to short-circuit the path search. The use of mapping files is not required for correct operation of the compiler, but mapping files can improve efficiency, particularly when sources are read over a slow network connection. In normal operation, you need not be concerned with the format or use of mapping files, and the @option{-gnatem} switch is not a switch that you would use explicitly. It is intended primarily for use by automatic tools such as @command{gnatmake} running under the project file facility. The description here of the format of mapping files is provided for completeness and for possible use by other tools. A mapping file is a sequence of sets of three lines. In each set, the first line is the unit name, in lower case, with @code{%s} appended for specs and @code{%b} appended for bodies; the second line is the file name; and the third line is the path name. Example: @smallexample main%b main.2.ada /gnat/project1/sources/main.2.ada @end smallexample When the switch @option{-gnatem} is specified, the compiler will create in memory the two mappings from the specified file. If there is any problem (nonexistent file, truncated file or duplicate entries), no mapping will be created. Several @option{-gnatem} switches may be specified; however, only the last one on the command line will be taken into account. When using a project file, @command{gnatmake} creates a temporary mapping file and communicates it to the compiler using this switch. @end table @node Integrated Preprocessing @subsection Integrated Preprocessing @noindent GNAT sources may be preprocessed immediately before compilation. In this case, the actual text of the source is not the text of the source file, but is derived from it through a process called preprocessing. Integrated preprocessing is specified through switches @option{-gnatep} and/or @option{-gnateD}. @option{-gnatep} indicates, through a text file, the preprocessing data to be used. @option{-gnateD} specifies or modifies the values of preprocessing symbol. @noindent Note that when integrated preprocessing is used, the output from the preprocessor is not written to any external file. Instead it is passed internally to the compiler. If you need to preserve the result of preprocessing in a file, then you should use @command{gnatprep} to perform the desired preprocessing in stand-alone mode. @noindent It is recommended that @command{gnatmake} switch ^-s^/SWITCH_CHECK^ should be used when Integrated Preprocessing is used. The reason is that preprocessing with another Preprocessing Data file without changing the sources will not trigger recompilation without this switch. @noindent Note that @command{gnatmake} switch ^-m^/MINIMAL_RECOMPILATION^ will almost always trigger recompilation for sources that are preprocessed, because @command{gnatmake} cannot compute the checksum of the source after preprocessing. @noindent The actual preprocessing function is described in details in section @ref{Preprocessing Using gnatprep}. This section only describes how integrated preprocessing is triggered and parameterized. @table @code @item -gnatep=@var{file} @cindex @option{-gnatep} (@command{gcc}) This switch indicates to the compiler the file name (without directory information) of the preprocessor data file to use. The preprocessor data file should be found in the source directories. @noindent A preprocessing data file is a text file with significant lines indicating how should be preprocessed either a specific source or all sources not mentioned in other lines. A significant line is a nonempty, non-comment line. Comments are similar to Ada comments. @noindent Each significant line starts with either a literal string or the character '*'. A literal string is the file name (without directory information) of the source to preprocess. A character '*' indicates the preprocessing for all the sources that are not specified explicitly on other lines (order of the lines is not significant). It is an error to have two lines with the same file name or two lines starting with the character '*'. @noindent After the file name or the character '*', another optional literal string indicating the file name of the definition file to be used for preprocessing (@pxref{Form of Definitions File}). The definition files are found by the compiler in one of the source directories. In some cases, when compiling a source in a directory other than the current directory, if the definition file is in the current directory, it may be necessary to add the current directory as a source directory through switch ^-I.^/SEARCH=[]^, otherwise the compiler would not find the definition file. @noindent Then, optionally, ^switches^switches^ similar to those of @code{gnatprep} may be found. Those ^switches^switches^ are: @table @code @item -b Causes both preprocessor lines and the lines deleted by preprocessing to be replaced by blank lines, preserving the line number. This ^switch^switch^ is always implied; however, if specified after @option{-c} it cancels the effect of @option{-c}. @item -c Causes both preprocessor lines and the lines deleted by preprocessing to be retained as comments marked with the special string ``@code{--! }''. @item -Dsymbol=value Define or redefine a symbol, associated with value. A symbol is an Ada identifier, or an Ada reserved word, with the exception of @code{if}, @code{else}, @code{elsif}, @code{end}, @code{and}, @code{or} and @code{then}. @code{value} is either a literal string, an Ada identifier or any Ada reserved word. A symbol declared with this ^switch^switch^ replaces a symbol with the same name defined in a definition file. @item -s Causes a sorted list of symbol names and values to be listed on the standard output file. @item -u Causes undefined symbols to be treated as having the value @code{FALSE} in the context of a preprocessor test. In the absence of this option, an undefined symbol in a @code{#if} or @code{#elsif} test will be treated as an error. @end table @noindent Examples of valid lines in a preprocessor data file: @smallexample "toto.adb" "prep.def" -u -- preprocess "toto.adb", using definition file "prep.def", -- undefined symbol are False. * -c -DVERSION=V101 -- preprocess all other sources without a definition file; -- suppressed lined are commented; symbol VERSION has the value V101. "titi.adb" "prep2.def" -s -- preprocess "titi.adb", using definition file "prep2.def"; -- list all symbols with their values. @end smallexample @item ^-gnateD^/DATA_PREPROCESSING=^symbol@r{[}=value@r{]} @cindex @option{-gnateD} (@command{gcc}) Define or redefine a preprocessing symbol, associated with value. If no value is given on the command line, then the value of the symbol is @code{True}. A symbol is an identifier, following normal Ada (case-insensitive) rules for its syntax, and value is any sequence (including an empty sequence) of characters from the set (letters, digits, period, underline). Ada reserved words may be used as symbols, with the exceptions of @code{if}, @code{else}, @code{elsif}, @code{end}, @code{and}, @code{or} and @code{then}. @noindent A symbol declared with this ^switch^switch^ on the command line replaces a symbol with the same name either in a definition file or specified with a ^switch^switch^ -D in the preprocessor data file. @noindent This switch is similar to switch @option{^-D^/ASSOCIATE^} of @code{gnatprep}. @item -gnateG When integrated preprocessing is performed and the preprocessor modifies the source text, write the result of this preprocessing into a file ^.prep^_prep^. @end table @node Code Generation Control @subsection Code Generation Control @noindent The GCC technology provides a wide range of target dependent @option{-m} switches for controlling details of code generation with respect to different versions of architectures. This includes variations in instruction sets (e.g.@: different members of the power pc family), and different requirements for optimal arrangement of instructions (e.g.@: different members of the x86 family). The list of available @option{-m} switches may be found in the GCC documentation. Use of these @option{-m} switches may in some cases result in improved code performance. The GNAT Pro technology is tested and qualified without any @option{-m} switches, so generally the most reliable approach is to avoid the use of these switches. However, we generally expect most of these switches to work successfully with GNAT Pro, and many customers have reported successful use of these options. Our general advice is to avoid the use of @option{-m} switches unless special needs lead to requirements in this area. In particular, there is no point in using @option{-m} switches to improve performance unless you actually see a performance improvement. @ifset vms @node Return Codes @subsection Return Codes @cindex Return Codes @cindex @option{/RETURN_CODES=VMS} @noindent On VMS, GNAT compiled programs return POSIX-style codes by default, e.g.@: @option{/RETURN_CODES=POSIX}. To enable VMS style return codes, use GNAT BIND and LINK with the option @option{/RETURN_CODES=VMS}. For example: @smallexample GNAT BIND MYMAIN.ALI /RETURN_CODES=VMS GNAT LINK MYMAIN.ALI /RETURN_CODES=VMS @end smallexample @noindent Programs built with /RETURN_CODES=VMS are suitable to be called in VMS DCL scripts. Programs compiled with the default /RETURN_CODES=POSIX are suitable for spawning with appropriate GNAT RTL routines. @end ifset @node Search Paths and the Run-Time Library (RTL) @section Search Paths and the Run-Time Library (RTL) @noindent With the GNAT source-based library system, the compiler must be able to find source files for units that are needed by the unit being compiled. Search paths are used to guide this process. The compiler compiles one source file whose name must be given explicitly on the command line. In other words, no searching is done for this file. To find all other source files that are needed (the most common being the specs of units), the compiler examines the following directories, in the following order: @enumerate @item The directory containing the source file of the main unit being compiled (the file name on the command line). @item Each directory named by an @option{^-I^/SOURCE_SEARCH^} switch given on the @command{gcc} command line, in the order given. @item @findex ADA_PRJ_INCLUDE_FILE Each of the directories listed in the text file whose name is given by the @env{ADA_PRJ_INCLUDE_FILE} ^environment variable^logical name^. @noindent @env{ADA_PRJ_INCLUDE_FILE} is normally set by gnatmake or by the ^gnat^GNAT^ driver when project files are used. It should not normally be set by other means. @item @findex ADA_INCLUDE_PATH Each of the directories listed in the value of the @env{ADA_INCLUDE_PATH} ^environment variable^logical name^. @ifclear vms Construct this value exactly as the @env{PATH} environment variable: a list of directory names separated by colons (semicolons when working with the NT version). @end ifclear @ifset vms Normally, define this value as a logical name containing a comma separated list of directory names. This variable can also be defined by means of an environment string (an argument to the HP C exec* set of functions). Logical Name: @smallexample DEFINE ANOTHER_PATH FOO:[BAG] DEFINE ADA_INCLUDE_PATH ANOTHER_PATH,FOO:[BAM],FOO:[BAR] @end smallexample By default, the path includes GNU:[LIB.OPENVMS7_x.2_8_x.DECLIB] first, followed by the standard Ada libraries in GNU:[LIB.OPENVMS7_x.2_8_x.ADAINCLUDE]. If this is not redefined, the user will obtain the HP Ada 83 IO packages (Text_IO, Sequential_IO, etc) instead of the standard Ada packages. Thus, in order to get the standard Ada packages by default, ADA_INCLUDE_PATH must be redefined. @end ifset @item The content of the @file{ada_source_path} file which is part of the GNAT installation tree and is used to store standard libraries such as the GNAT Run Time Library (RTL) source files. @ifclear vms @ref{Installing a library} @end ifclear @end enumerate @noindent Specifying the switch @option{^-I-^/NOCURRENT_DIRECTORY^} inhibits the use of the directory containing the source file named in the command line. You can still have this directory on your search path, but in this case it must be explicitly requested with a @option{^-I^/SOURCE_SEARCH^} switch. Specifying the switch @option{-nostdinc} inhibits the search of the default location for the GNAT Run Time Library (RTL) source files. The compiler outputs its object files and ALI files in the current working directory. @ifclear vms Caution: The object file can be redirected with the @option{-o} switch; however, @command{gcc} and @code{gnat1} have not been coordinated on this so the @file{ALI} file will not go to the right place. Therefore, you should avoid using the @option{-o} switch. @end ifclear @findex System.IO The packages @code{Ada}, @code{System}, and @code{Interfaces} and their children make up the GNAT RTL, together with the simple @code{System.IO} package used in the @code{"Hello World"} example. The sources for these units are needed by the compiler and are kept together in one directory. Not all of the bodies are needed, but all of the sources are kept together anyway. In a normal installation, you need not specify these directory names when compiling or binding. Either the environment variables or the built-in defaults cause these files to be found. In addition to the language-defined hierarchies (@code{System}, @code{Ada} and @code{Interfaces}), the GNAT distribution provides a fourth hierarchy, consisting of child units of @code{GNAT}. This is a collection of generally useful types, subprograms, etc. @xref{Top, GNAT Reference Manual, About This Guid, gnat_rm, GNAT Reference Manual}, for further details. Besides simplifying access to the RTL, a major use of search paths is in compiling sources from multiple directories. This can make development environments much more flexible. @node Order of Compilation Issues @section Order of Compilation Issues @noindent If, in our earlier example, there was a spec for the @code{hello} procedure, it would be contained in the file @file{hello.ads}; yet this file would not have to be explicitly compiled. This is the result of the model we chose to implement library management. Some of the consequences of this model are as follows: @itemize @bullet @item There is no point in compiling specs (except for package specs with no bodies) because these are compiled as needed by clients. If you attempt a useless compilation, you will receive an error message. It is also useless to compile subunits because they are compiled as needed by the parent. @item There are no order of compilation requirements: performing a compilation never obsoletes anything. The only way you can obsolete something and require recompilations is to modify one of the source files on which it depends. @item There is no library as such, apart from the ALI files (@pxref{The Ada Library Information Files}, for information on the format of these files). For now we find it convenient to create separate ALI files, but eventually the information therein may be incorporated into the object file directly. @item When you compile a unit, the source files for the specs of all units that it @code{with}'s, all its subunits, and the bodies of any generics it instantiates must be available (reachable by the search-paths mechanism described above), or you will receive a fatal error message. @end itemize @node Examples @section Examples @noindent The following are some typical Ada compilation command line examples: @table @code @item $ gcc -c xyz.adb Compile body in file @file{xyz.adb} with all default options. @ifclear vms @item $ gcc -c -O2 -gnata xyz-def.adb @end ifclear @ifset vms @item $ GNAT COMPILE /OPTIMIZE=ALL -gnata xyz-def.adb @end ifset Compile the child unit package in file @file{xyz-def.adb} with extensive optimizations, and pragma @code{Assert}/@code{Debug} statements enabled. @item $ gcc -c -gnatc abc-def.adb Compile the subunit in file @file{abc-def.adb} in semantic-checking-only mode. @end table @node Binding Using gnatbind @chapter Binding Using @code{gnatbind} @findex gnatbind @menu * Running gnatbind:: * Switches for gnatbind:: * Command-Line Access:: * Search Paths for gnatbind:: * Examples of gnatbind Usage:: @end menu @noindent This chapter describes the GNAT binder, @code{gnatbind}, which is used to bind compiled GNAT objects. Note: to invoke @code{gnatbind} with a project file, use the @code{gnat} driver (see @ref{The GNAT Driver and Project Files}). The @code{gnatbind} program performs four separate functions: @enumerate @item Checks that a program is consistent, in accordance with the rules in Chapter 10 of the Ada Reference Manual. In particular, error messages are generated if a program uses inconsistent versions of a given unit. @item Checks that an acceptable order of elaboration exists for the program and issues an error message if it cannot find an order of elaboration that satisfies the rules in Chapter 10 of the Ada Language Manual. @item Generates a main program incorporating the given elaboration order. This program is a small Ada package (body and spec) that must be subsequently compiled using the GNAT compiler. The necessary compilation step is usually performed automatically by @command{gnatlink}. The two most important functions of this program are to call the elaboration routines of units in an appropriate order and to call the main program. @item Determines the set of object files required by the given main program. This information is output in the forms of comments in the generated program, to be read by the @command{gnatlink} utility used to link the Ada application. @end enumerate @node Running gnatbind @section Running @code{gnatbind} @noindent The form of the @code{gnatbind} command is @smallexample @c $ gnatbind @ovar{switches} @var{mainprog}@r{[}.ali@r{]} @ovar{switches} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatbind @r{[}@var{switches}@r{]} @var{mainprog}@r{[}.ali@r{]} @r{[}@var{switches}@r{]} @end smallexample @noindent where @file{@var{mainprog}.adb} is the Ada file containing the main program unit body. @code{gnatbind} constructs an Ada package in two files whose names are @file{b~@var{mainprog}.ads}, and @file{b~@var{mainprog}.adb}. For example, if given the parameter @file{hello.ali}, for a main program contained in file @file{hello.adb}, the binder output files would be @file{b~hello.ads} and @file{b~hello.adb}. When doing consistency checking, the binder takes into consideration any source files it can locate. For example, if the binder determines that the given main program requires the package @code{Pack}, whose @file{.ALI} file is @file{pack.ali} and whose corresponding source spec file is @file{pack.ads}, it attempts to locate the source file @file{pack.ads} (using the same search path conventions as previously described for the @command{gcc} command). If it can locate this source file, it checks that the time stamps or source checksums of the source and its references to in @file{ALI} files match. In other words, any @file{ALI} files that mentions this spec must have resulted from compiling this version of the source file (or in the case where the source checksums match, a version close enough that the difference does not matter). @cindex Source files, use by binder The effect of this consistency checking, which includes source files, is that the binder ensures that the program is consistent with the latest version of the source files that can be located at bind time. Editing a source file without compiling files that depend on the source file cause error messages to be generated by the binder. For example, suppose you have a main program @file{hello.adb} and a package @code{P}, from file @file{p.ads} and you perform the following steps: @enumerate @item Enter @code{gcc -c hello.adb} to compile the main program. @item Enter @code{gcc -c p.ads} to compile package @code{P}. @item Edit file @file{p.ads}. @item Enter @code{gnatbind hello}. @end enumerate @noindent At this point, the file @file{p.ali} contains an out-of-date time stamp because the file @file{p.ads} has been edited. The attempt at binding fails, and the binder generates the following error messages: @smallexample error: "hello.adb" must be recompiled ("p.ads" has been modified) error: "p.ads" has been modified and must be recompiled @end smallexample @noindent Now both files must be recompiled as indicated, and then the bind can succeed, generating a main program. You need not normally be concerned with the contents of this file, but for reference purposes a sample binder output file is given in @ref{Example of Binder Output File}. In most normal usage, the default mode of @command{gnatbind} which is to generate the main package in Ada, as described in the previous section. In particular, this means that any Ada programmer can read and understand the generated main program. It can also be debugged just like any other Ada code provided the @option{^-g^/DEBUG^} switch is used for @command{gnatbind} and @command{gnatlink}. @node Switches for gnatbind @section Switches for @command{gnatbind} @noindent The following switches are available with @code{gnatbind}; details will be presented in subsequent sections. @menu * Consistency-Checking Modes:: * Binder Error Message Control:: * Elaboration Control:: * Output Control:: * Dynamic Allocation Control:: * Binding with Non-Ada Main Programs:: * Binding Programs with No Main Subprogram:: @end menu @table @option @c !sort! @item --version @cindex @option{--version} @command{gnatbind} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatbind} If @option{--version} was not used, display usage, then exit disregarding all other options. @item -a @cindex @option{-a} @command{gnatbind} Indicates that, if supported by the platform, the adainit procedure should be treated as an initialisation routine by the linker (a constructor). This is intended to be used by the Project Manager to automatically initialize shared Stand-Alone Libraries. @item ^-aO^/OBJECT_SEARCH^ @cindex @option{^-aO^/OBJECT_SEARCH^} (@command{gnatbind}) Specify directory to be searched for ALI files. @item ^-aI^/SOURCE_SEARCH^ @cindex @option{^-aI^/SOURCE_SEARCH^} (@command{gnatbind}) Specify directory to be searched for source file. @item ^-A^/ALI_LIST^@r{[=}@var{filename}@r{]} @cindex @option{^-A^/ALI_LIST^} (@command{gnatbind}) Output ALI list (to standard output or to the named file). @item ^-b^/REPORT_ERRORS=BRIEF^ @cindex @option{^-b^/REPORT_ERRORS=BRIEF^} (@command{gnatbind}) Generate brief messages to @file{stderr} even if verbose mode set. @item ^-c^/NOOUTPUT^ @cindex @option{^-c^/NOOUTPUT^} (@command{gnatbind}) Check only, no generation of binder output file. @item ^-d^/DEFAULT_STACK_SIZE=^@var{nn}@r{[}k@r{|}m@r{]} @cindex @option{^-d^/DEFAULT_STACK_SIZE=^@var{nn}@r{[}k@r{|}m@r{]}} (@command{gnatbind}) This switch can be used to change the default task stack size value to a specified size @var{nn}, which is expressed in bytes by default, or in kilobytes when suffixed with @var{k} or in megabytes when suffixed with @var{m}. In the absence of a @samp{@r{[}k@r{|}m@r{]}} suffix, this switch is equivalent, in effect, to completing all task specs with @smallexample @c ada pragma Storage_Size (nn); @end smallexample When they do not already have such a pragma. @item ^-D^/DEFAULT_SECONDARY_STACK_SIZE=^@var{nn}@r{[}k@r{|}m@r{]} @cindex @option{^-D^/DEFAULT_SECONDARY_STACK_SIZE=nnnnn^} (@command{gnatbind}) This switch can be used to change the default secondary stack size value to a specified size @var{nn}, which is expressed in bytes by default, or in kilobytes when suffixed with @var{k} or in megabytes when suffixed with @var{m}. The secondary stack is used to deal with functions that return a variable sized result, for example a function returning an unconstrained String. There are two ways in which this secondary stack is allocated. For most targets, the secondary stack is growing on demand and is allocated as a chain of blocks in the heap. The -D option is not very relevant. It only give some control over the size of the allocated blocks (whose size is the minimum of the default secondary stack size value, and the actual size needed for the current allocation request). For certain targets, notably VxWorks 653, the secondary stack is allocated by carving off a fixed ratio chunk of the primary task stack. The -D option is used to define the size of the environment task's secondary stack. @item ^-e^/ELABORATION_DEPENDENCIES^ @cindex @option{^-e^/ELABORATION_DEPENDENCIES^} (@command{gnatbind}) Output complete list of elaboration-order dependencies. @item ^-E^/STORE_TRACEBACKS^ @cindex @option{^-E^/STORE_TRACEBACKS^} (@command{gnatbind}) Store tracebacks in exception occurrences when the target supports it. @ignore @c The following may get moved to an appendix This option is currently supported on the following targets: all x86 ports, Solaris, Windows, HP-UX, AIX, PowerPC VxWorks and Alpha VxWorks. @end ignore See also the packages @code{GNAT.Traceback} and @code{GNAT.Traceback.Symbolic} for more information. @ifclear vms Note that on x86 ports, you must not use @option{-fomit-frame-pointer} @command{gcc} option. @end ifclear @item ^-F^/FORCE_ELABS_FLAGS^ @cindex @option{^-F^/FORCE_ELABS_FLAGS^} (@command{gnatbind}) Force the checks of elaboration flags. @command{gnatbind} does not normally generate checks of elaboration flags for the main executable, except when a Stand-Alone Library is used. However, there are cases when this cannot be detected by gnatbind. An example is importing an interface of a Stand-Alone Library through a pragma Import and only specifying through a linker switch this Stand-Alone Library. This switch is used to guarantee that elaboration flag checks are generated. @item ^-h^/HELP^ @cindex @option{^-h^/HELP^} (@command{gnatbind}) Output usage (help) information @item ^-H32^/32_MALLOC^ @cindex @option{^-H32^/32_MALLOC^} (@command{gnatbind}) Use 32-bit allocations for @code{__gnat_malloc} (and thus for access types). For further details see @ref{Dynamic Allocation Control}. @item ^-H64^/64_MALLOC^ @cindex @option{^-H32^/32_MALLOC^} (@command{gnatbind}) Use 64-bit allocations for @code{__gnat_malloc} (and thus for access types). @cindex @code{__gnat_malloc} For further details see @ref{Dynamic Allocation Control}. @item ^-I^/SEARCH^ @cindex @option{^-I^/SEARCH^} (@command{gnatbind}) Specify directory to be searched for source and ALI files. @item ^-I-^/NOCURRENT_DIRECTORY^ @cindex @option{^-I-^/NOCURRENT_DIRECTORY^} (@command{gnatbind}) Do not look for sources in the current directory where @code{gnatbind} was invoked, and do not look for ALI files in the directory containing the ALI file named in the @code{gnatbind} command line. @item ^-l^/ORDER_OF_ELABORATION^ @cindex @option{^-l^/ORDER_OF_ELABORATION^} (@command{gnatbind}) Output chosen elaboration order. @item ^-L@var{xxx}^/BUILD_LIBRARY=@var{xxx}^ @cindex @option{^-L^/BUILD_LIBRARY^} (@command{gnatbind}) Bind the units for library building. In this case the adainit and adafinal procedures (@pxref{Binding with Non-Ada Main Programs}) are renamed to ^@var{xxx}init^@var{XXX}INIT^ and ^@var{xxx}final^@var{XXX}FINAL^. Implies ^-n^/NOCOMPILE^. @ifclear vms (@xref{GNAT and Libraries}, for more details.) @end ifclear @ifset vms On OpenVMS, these init and final procedures are exported in uppercase letters. For example if /BUILD_LIBRARY=toto is used, the exported name of the init procedure will be "TOTOINIT" and the exported name of the final procedure will be "TOTOFINAL". @end ifset @item ^-Mxyz^/RENAME_MAIN=xyz^ @cindex @option{^-M^/RENAME_MAIN^} (@command{gnatbind}) Rename generated main program from main to xyz. This option is supported on cross environments only. @item ^-m^/ERROR_LIMIT=^@var{n} @cindex @option{^-m^/ERROR_LIMIT^} (@command{gnatbind}) Limit number of detected errors or warnings to @var{n}, where @var{n} is in the range 1..999999. The default value if no switch is given is 9999. If the number of warnings reaches this limit, then a message is output and further warnings are suppressed, the bind continues in this case. If the number of errors reaches this limit, then a message is output and the bind is abandoned. A value of zero means that no limit is enforced. The equal sign is optional. @ifset unw Furthermore, under Windows, the sources pointed to by the libraries path set in the registry are not searched for. @end ifset @item ^-n^/NOMAIN^ @cindex @option{^-n^/NOMAIN^} (@command{gnatbind}) No main program. @item -nostdinc @cindex @option{-nostdinc} (@command{gnatbind}) Do not look for sources in the system default directory. @item -nostdlib @cindex @option{-nostdlib} (@command{gnatbind}) Do not look for library files in the system default directory. @item --RTS=@var{rts-path} @cindex @option{--RTS} (@code{gnatbind}) Specifies the default location of the runtime library. Same meaning as the equivalent @command{gnatmake} flag (@pxref{Switches for gnatmake}). @item ^-o ^/OUTPUT=^@var{file} @cindex @option{^-o ^/OUTPUT^} (@command{gnatbind}) Name the output file @var{file} (default is @file{b~@var{xxx}.adb}). Note that if this option is used, then linking must be done manually, gnatlink cannot be used. @item ^-O^/OBJECT_LIST^@r{[=}@var{filename}@r{]} @cindex @option{^-O^/OBJECT_LIST^} (@command{gnatbind}) Output object list (to standard output or to the named file). @item ^-p^/PESSIMISTIC_ELABORATION^ @cindex @option{^-p^/PESSIMISTIC_ELABORATION^} (@command{gnatbind}) Pessimistic (worst-case) elaboration order @item ^-R^-R^ @cindex @option{^-R^-R^} (@command{gnatbind}) Output closure source list. @item ^-s^/READ_SOURCES=ALL^ @cindex @option{^-s^/READ_SOURCES=ALL^} (@command{gnatbind}) Require all source files to be present. @item ^-S@var{xxx}^/INITIALIZE_SCALARS=@var{xxx}^ @cindex @option{^-S^/INITIALIZE_SCALARS^} (@command{gnatbind}) Specifies the value to be used when detecting uninitialized scalar objects with pragma Initialize_Scalars. The @var{xxx} ^string specified with the switch^option^ may be either @itemize @bullet @item ``@option{^in^INVALID^}'' requesting an invalid value where possible @item ``@option{^lo^LOW^}'' for the lowest possible value @item ``@option{^hi^HIGH^}'' for the highest possible value @item ``@option{@var{xx}}'' for a value consisting of repeated bytes with the value @code{16#@var{xx}#} (i.e., @var{xx} is a string of two hexadecimal digits). @end itemize In addition, you can specify @option{-Sev} to indicate that the value is to be set at run time. In this case, the program will look for an environment @cindex GNAT_INIT_SCALARS variable of the form @env{GNAT_INIT_SCALARS=@var{xx}}, where @var{xx} is one of @option{in/lo/hi/@var{xx}} with the same meanings as above. If no environment variable is found, or if it does not have a valid value, then the default is @option{in} (invalid values). @ifclear vms @item -static @cindex @option{-static} (@code{gnatbind}) Link against a static GNAT run time. @item -shared @cindex @option{-shared} (@code{gnatbind}) Link against a shared GNAT run time when available. @end ifclear @item ^-t^/NOTIME_STAMP_CHECK^ @cindex @option{^-t^/NOTIME_STAMP_CHECK^} (@code{gnatbind}) Tolerate time stamp and other consistency errors @item ^-T@var{n}^/TIME_SLICE=@var{n}^ @cindex @option{^-T^/TIME_SLICE^} (@code{gnatbind}) Set the time slice value to @var{n} milliseconds. If the system supports the specification of a specific time slice value, then the indicated value is used. If the system does not support specific time slice values, but does support some general notion of round-robin scheduling, then any nonzero value will activate round-robin scheduling. A value of zero is treated specially. It turns off time slicing, and in addition, indicates to the tasking run time that the semantics should match as closely as possible the Annex D requirements of the Ada RM, and in particular sets the default scheduling policy to @code{FIFO_Within_Priorities}. @item ^-u@var{n}^/DYNAMIC_STACK_USAGE=@var{n}^ @cindex @option{^-u^/DYNAMIC_STACK_USAGE^} (@code{gnatbind}) Enable dynamic stack usage, with @var{n} results stored and displayed at program termination. A result is generated when a task terminates. Results that can't be stored are displayed on the fly, at task termination. This option is currently not supported on Itanium platforms. (See @ref{Dynamic Stack Usage Analysis} for details.) @item ^-v^/REPORT_ERRORS=VERBOSE^ @cindex @option{^-v^/REPORT_ERRORS=VERBOSE^} (@code{gnatbind}) Verbose mode. Write error messages, header, summary output to @file{stdout}. @ifclear vms @item -w@var{x} @cindex @option{-w} (@code{gnatbind}) Warning mode (@var{x}=s/e for suppress/treat as error) @end ifclear @ifset vms @item /WARNINGS=NORMAL @cindex @option{/WARNINGS} (@code{gnatbind}) Normal warnings mode. Warnings are issued but ignored @item /WARNINGS=SUPPRESS @cindex @option{/WARNINGS} (@code{gnatbind}) All warning messages are suppressed @item /WARNINGS=ERROR @cindex @option{/WARNINGS} (@code{gnatbind}) Warning messages are treated as fatal errors @end ifset @item ^-Wx^/WIDE_CHARACTER_ENCODING=^@var{e} @cindex @option{^-Wx^/WIDE_CHARACTER_ENCODING^} (@code{gnatbind}) Override default wide character encoding for standard Text_IO files. @item ^-x^/READ_SOURCES=NONE^ @cindex @option{^-x^/READ_SOURCES^} (@code{gnatbind}) Exclude source files (check object consistency only). @ifset vms @item /READ_SOURCES=AVAILABLE @cindex @option{/READ_SOURCES} (@code{gnatbind}) Default mode, in which sources are checked for consistency only if they are available. @end ifset @item ^-y^/ENABLE_LEAP_SECONDS^ @cindex @option{^-y^/ENABLE_LEAP_SECONDS^} (@code{gnatbind}) Enable leap seconds support in @code{Ada.Calendar} and its children. @item ^-z^/ZERO_MAIN^ @cindex @option{^-z^/ZERO_MAIN^} (@code{gnatbind}) No main subprogram. @end table @ifclear vms @noindent You may obtain this listing of switches by running @code{gnatbind} with no arguments. @end ifclear @node Consistency-Checking Modes @subsection Consistency-Checking Modes @noindent As described earlier, by default @code{gnatbind} checks that object files are consistent with one another and are consistent with any source files it can locate. The following switches control binder access to sources. @table @option @c !sort! @item ^-s^/READ_SOURCES=ALL^ @cindex @option{^-s^/READ_SOURCES=ALL^} (@code{gnatbind}) Require source files to be present. In this mode, the binder must be able to locate all source files that are referenced, in order to check their consistency. In normal mode, if a source file cannot be located it is simply ignored. If you specify this switch, a missing source file is an error. @item ^-Wx^/WIDE_CHARACTER_ENCODING=^@var{e} @cindex @option{^-Wx^/WIDE_CHARACTER_ENCODING^} (@code{gnatbind}) Override default wide character encoding for standard Text_IO files. Normally the default wide character encoding method used for standard [Wide_[Wide_]]Text_IO files is taken from the encoding specified for the main source input (see description of switch @option{^-gnatWx^/WIDE_CHARACTER_ENCODING^} for the compiler). The use of this switch for the binder (which has the same set of possible arguments) overrides this default as specified. @item ^-x^/READ_SOURCES=NONE^ @cindex @option{^-x^/READ_SOURCES=NONE^} (@code{gnatbind}) Exclude source files. In this mode, the binder only checks that ALI files are consistent with one another. Source files are not accessed. The binder runs faster in this mode, and there is still a guarantee that the resulting program is self-consistent. If a source file has been edited since it was last compiled, and you specify this switch, the binder will not detect that the object file is out of date with respect to the source file. Note that this is the mode that is automatically used by @command{gnatmake} because in this case the checking against sources has already been performed by @command{gnatmake} in the course of compilation (i.e.@: before binding). @ifset vms @item /READ_SOURCES=AVAILABLE @cindex @code{/READ_SOURCES=AVAILABLE} (@code{gnatbind}) This is the default mode in which source files are checked if they are available, and ignored if they are not available. @end ifset @end table @node Binder Error Message Control @subsection Binder Error Message Control @noindent The following switches provide control over the generation of error messages from the binder: @table @option @c !sort! @item ^-v^/REPORT_ERRORS=VERBOSE^ @cindex @option{^-v^/REPORT_ERRORS=VERBOSE^} (@code{gnatbind}) Verbose mode. In the normal mode, brief error messages are generated to @file{stderr}. If this switch is present, a header is written to @file{stdout} and any error messages are directed to @file{stdout}. All that is written to @file{stderr} is a brief summary message. @item ^-b^/REPORT_ERRORS=BRIEF^ @cindex @option{^-b^/REPORT_ERRORS=BRIEF^} (@code{gnatbind}) Generate brief error messages to @file{stderr} even if verbose mode is specified. This is relevant only when used with the @option{^-v^/REPORT_ERRORS=VERBOSE^} switch. @ifclear vms @item -m@var{n} @cindex @option{-m} (@code{gnatbind}) Limits the number of error messages to @var{n}, a decimal integer in the range 1-999. The binder terminates immediately if this limit is reached. @item -M@var{xxx} @cindex @option{-M} (@code{gnatbind}) Renames the generated main program from @code{main} to @code{xxx}. This is useful in the case of some cross-building environments, where the actual main program is separate from the one generated by @code{gnatbind}. @end ifclear @item ^-ws^/WARNINGS=SUPPRESS^ @cindex @option{^-ws^/WARNINGS=SUPPRESS^} (@code{gnatbind}) @cindex Warnings Suppress all warning messages. @item ^-we^/WARNINGS=ERROR^ @cindex @option{^-we^/WARNINGS=ERROR^} (@code{gnatbind}) Treat any warning messages as fatal errors. @ifset vms @item /WARNINGS=NORMAL Standard mode with warnings generated, but warnings do not get treated as errors. @end ifset @item ^-t^/NOTIME_STAMP_CHECK^ @cindex @option{^-t^/NOTIME_STAMP_CHECK^} (@code{gnatbind}) @cindex Time stamp checks, in binder @cindex Binder consistency checks @cindex Consistency checks, in binder The binder performs a number of consistency checks including: @itemize @bullet @item Check that time stamps of a given source unit are consistent @item Check that checksums of a given source unit are consistent @item Check that consistent versions of @code{GNAT} were used for compilation @item Check consistency of configuration pragmas as required @end itemize @noindent Normally failure of such checks, in accordance with the consistency requirements of the Ada Reference Manual, causes error messages to be generated which abort the binder and prevent the output of a binder file and subsequent link to obtain an executable. The @option{^-t^/NOTIME_STAMP_CHECK^} switch converts these error messages into warnings, so that binding and linking can continue to completion even in the presence of such errors. The result may be a failed link (due to missing symbols), or a non-functional executable which has undefined semantics. @emph{This means that @option{^-t^/NOTIME_STAMP_CHECK^} should be used only in unusual situations, with extreme care.} @end table @node Elaboration Control @subsection Elaboration Control @noindent The following switches provide additional control over the elaboration order. For full details see @ref{Elaboration Order Handling in GNAT}. @table @option @item ^-p^/PESSIMISTIC_ELABORATION^ @cindex @option{^-p^/PESSIMISTIC_ELABORATION^} (@code{gnatbind}) Normally the binder attempts to choose an elaboration order that is likely to minimize the likelihood of an elaboration order error resulting in raising a @code{Program_Error} exception. This switch reverses the action of the binder, and requests that it deliberately choose an order that is likely to maximize the likelihood of an elaboration error. This is useful in ensuring portability and avoiding dependence on accidental fortuitous elaboration ordering. Normally it only makes sense to use the @option{^-p^/PESSIMISTIC_ELABORATION^} switch if dynamic elaboration checking is used (@option{-gnatE} switch used for compilation). This is because in the default static elaboration mode, all necessary @code{Elaborate} and @code{Elaborate_All} pragmas are implicitly inserted. These implicit pragmas are still respected by the binder in @option{^-p^/PESSIMISTIC_ELABORATION^} mode, so a safe elaboration order is assured. @end table @node Output Control @subsection Output Control @noindent The following switches allow additional control over the output generated by the binder. @table @option @c !sort! @item ^-c^/NOOUTPUT^ @cindex @option{^-c^/NOOUTPUT^} (@code{gnatbind}) Check only. Do not generate the binder output file. In this mode the binder performs all error checks but does not generate an output file. @item ^-e^/ELABORATION_DEPENDENCIES^ @cindex @option{^-e^/ELABORATION_DEPENDENCIES^} (@code{gnatbind}) Output complete list of elaboration-order dependencies, showing the reason for each dependency. This output can be rather extensive but may be useful in diagnosing problems with elaboration order. The output is written to @file{stdout}. @item ^-h^/HELP^ @cindex @option{^-h^/HELP^} (@code{gnatbind}) Output usage information. The output is written to @file{stdout}. @item ^-K^/LINKER_OPTION_LIST^ @cindex @option{^-K^/LINKER_OPTION_LIST^} (@code{gnatbind}) Output linker options to @file{stdout}. Includes library search paths, contents of pragmas Ident and Linker_Options, and libraries added by @code{gnatbind}. @item ^-l^/ORDER_OF_ELABORATION^ @cindex @option{^-l^/ORDER_OF_ELABORATION^} (@code{gnatbind}) Output chosen elaboration order. The output is written to @file{stdout}. @item ^-O^/OBJECT_LIST^ @cindex @option{^-O^/OBJECT_LIST^} (@code{gnatbind}) Output full names of all the object files that must be linked to provide the Ada component of the program. The output is written to @file{stdout}. This list includes the files explicitly supplied and referenced by the user as well as implicitly referenced run-time unit files. The latter are omitted if the corresponding units reside in shared libraries. The directory names for the run-time units depend on the system configuration. @item ^-o ^/OUTPUT=^@var{file} @cindex @option{^-o^/OUTPUT^} (@code{gnatbind}) Set name of output file to @var{file} instead of the normal @file{b~@var{mainprog}.adb} default. Note that @var{file} denote the Ada binder generated body filename. Note that if this option is used, then linking must be done manually. It is not possible to use gnatlink in this case, since it cannot locate the binder file. @item ^-r^/RESTRICTION_LIST^ @cindex @option{^-r^/RESTRICTION_LIST^} (@code{gnatbind}) Generate list of @code{pragma Restrictions} that could be applied to the current unit. This is useful for code audit purposes, and also may be used to improve code generation in some cases. @end table @node Dynamic Allocation Control @subsection Dynamic Allocation Control @noindent The heap control switches -- @option{-H32} and @option{-H64} -- determine whether dynamic allocation uses 32-bit or 64-bit memory. They only affect compiler-generated allocations via @code{__gnat_malloc}; explicit calls to @code{malloc} and related functions from the C run-time library are unaffected. @table @option @item -H32 Allocate memory on 32-bit heap @item -H64 Allocate memory on 64-bit heap. This is the default unless explicitly overridden by a @code{'Size} clause on the access type. @end table @ifset vms @noindent See also @ref{Access types and 32/64-bit allocation}. @end ifset @ifclear vms @noindent These switches are only effective on VMS platforms. @end ifclear @node Binding with Non-Ada Main Programs @subsection Binding with Non-Ada Main Programs @noindent In our description so far we have assumed that the main program is in Ada, and that the task of the binder is to generate a corresponding function @code{main} that invokes this Ada main program. GNAT also supports the building of executable programs where the main program is not in Ada, but some of the called routines are written in Ada and compiled using GNAT (@pxref{Mixed Language Programming}). The following switch is used in this situation: @table @option @item ^-n^/NOMAIN^ @cindex @option{^-n^/NOMAIN^} (@code{gnatbind}) No main program. The main program is not in Ada. @end table @noindent In this case, most of the functions of the binder are still required, but instead of generating a main program, the binder generates a file containing the following callable routines: @table @code @item adainit @findex adainit You must call this routine to initialize the Ada part of the program by calling the necessary elaboration routines. A call to @code{adainit} is required before the first call to an Ada subprogram. Note that it is assumed that the basic execution environment must be setup to be appropriate for Ada execution at the point where the first Ada subprogram is called. In particular, if the Ada code will do any floating-point operations, then the FPU must be setup in an appropriate manner. For the case of the x86, for example, full precision mode is required. The procedure GNAT.Float_Control.Reset may be used to ensure that the FPU is in the right state. @item adafinal @findex adafinal You must call this routine to perform any library-level finalization required by the Ada subprograms. A call to @code{adafinal} is required after the last call to an Ada subprogram, and before the program terminates. @end table @noindent If the @option{^-n^/NOMAIN^} switch @cindex @option{^-n^/NOMAIN^} (@command{gnatbind}) @cindex Binder, multiple input files is given, more than one ALI file may appear on the command line for @code{gnatbind}. The normal @dfn{closure} calculation is performed for each of the specified units. Calculating the closure means finding out the set of units involved by tracing @code{with} references. The reason it is necessary to be able to specify more than one ALI file is that a given program may invoke two or more quite separate groups of Ada units. The binder takes the name of its output file from the last specified ALI file, unless overridden by the use of the @option{^-o file^/OUTPUT=file^}. @cindex @option{^-o^/OUTPUT^} (@command{gnatbind}) The output is an Ada unit in source form that can be compiled with GNAT. This compilation occurs automatically as part of the @command{gnatlink} processing. Currently the GNAT run time requires a FPU using 80 bits mode precision. Under targets where this is not the default it is required to call GNAT.Float_Control.Reset before using floating point numbers (this include float computation, float input and output) in the Ada code. A side effect is that this could be the wrong mode for the foreign code where floating point computation could be broken after this call. @node Binding Programs with No Main Subprogram @subsection Binding Programs with No Main Subprogram @noindent It is possible to have an Ada program which does not have a main subprogram. This program will call the elaboration routines of all the packages, then the finalization routines. The following switch is used to bind programs organized in this manner: @table @option @item ^-z^/ZERO_MAIN^ @cindex @option{^-z^/ZERO_MAIN^} (@code{gnatbind}) Normally the binder checks that the unit name given on the command line corresponds to a suitable main subprogram. When this switch is used, a list of ALI files can be given, and the execution of the program consists of elaboration of these units in an appropriate order. Note that the default wide character encoding method for standard Text_IO files is always set to Brackets if this switch is set (you can use the binder switch @option{^-Wx^WIDE_CHARACTER_ENCODING^} to override this default). @end table @node Command-Line Access @section Command-Line Access @noindent The package @code{Ada.Command_Line} provides access to the command-line arguments and program name. In order for this interface to operate correctly, the two variables @smallexample @group int gnat_argc; char **gnat_argv; @end group @end smallexample @noindent @findex gnat_argv @findex gnat_argc are declared in one of the GNAT library routines. These variables must be set from the actual @code{argc} and @code{argv} values passed to the main program. With no @option{^n^/NOMAIN^} present, @code{gnatbind} generates the C main program to automatically set these variables. If the @option{^n^/NOMAIN^} switch is used, there is no automatic way to set these variables. If they are not set, the procedures in @code{Ada.Command_Line} will not be available, and any attempt to use them will raise @code{Constraint_Error}. If command line access is required, your main program must set @code{gnat_argc} and @code{gnat_argv} from the @code{argc} and @code{argv} values passed to it. @node Search Paths for gnatbind @section Search Paths for @code{gnatbind} @noindent The binder takes the name of an ALI file as its argument and needs to locate source files as well as other ALI files to verify object consistency. For source files, it follows exactly the same search rules as @command{gcc} (@pxref{Search Paths and the Run-Time Library (RTL)}). For ALI files the directories searched are: @enumerate @item The directory containing the ALI file named in the command line, unless the switch @option{^-I-^/NOCURRENT_DIRECTORY^} is specified. @item All directories specified by @option{^-I^/SEARCH^} switches on the @code{gnatbind} command line, in the order given. @item @findex ADA_PRJ_OBJECTS_FILE Each of the directories listed in the text file whose name is given by the @env{ADA_PRJ_OBJECTS_FILE} ^environment variable^logical name^. @noindent @env{ADA_PRJ_OBJECTS_FILE} is normally set by gnatmake or by the ^gnat^GNAT^ driver when project files are used. It should not normally be set by other means. @item @findex ADA_OBJECTS_PATH Each of the directories listed in the value of the @env{ADA_OBJECTS_PATH} ^environment variable^logical name^. @ifset unw Construct this value exactly as the @env{PATH} environment variable: a list of directory names separated by colons (semicolons when working with the NT version of GNAT). @end ifset @ifset vms Normally, define this value as a logical name containing a comma separated list of directory names. This variable can also be defined by means of an environment string (an argument to the HP C exec* set of functions). Logical Name: @smallexample DEFINE ANOTHER_PATH FOO:[BAG] DEFINE ADA_OBJECTS_PATH ANOTHER_PATH,FOO:[BAM],FOO:[BAR] @end smallexample By default, the path includes GNU:[LIB.OPENVMS7_x.2_8_x.DECLIB] first, followed by the standard Ada libraries in GNU:[LIB.OPENVMS7_x.2_8_x.ADALIB]. If this is not redefined, the user will obtain the HP Ada 83 IO packages (Text_IO, Sequential_IO, etc) instead of the standard Ada packages. Thus, in order to get the standard Ada packages by default, ADA_OBJECTS_PATH must be redefined. @end ifset @item The content of the @file{ada_object_path} file which is part of the GNAT installation tree and is used to store standard libraries such as the GNAT Run Time Library (RTL) unless the switch @option{-nostdlib} is specified. @ifclear vms @ref{Installing a library} @end ifclear @end enumerate @noindent In the binder the switch @option{^-I^/SEARCH^} @cindex @option{^-I^/SEARCH^} (@command{gnatbind}) is used to specify both source and library file paths. Use @option{^-aI^/SOURCE_SEARCH^} @cindex @option{^-aI^/SOURCE_SEARCH^} (@command{gnatbind}) instead if you want to specify source paths only, and @option{^-aO^/LIBRARY_SEARCH^} @cindex @option{^-aO^/LIBRARY_SEARCH^} (@command{gnatbind}) if you want to specify library paths only. This means that for the binder @option{^-I^/SEARCH=^}@var{dir} is equivalent to @option{^-aI^/SOURCE_SEARCH=^}@var{dir} @option{^-aO^/OBJECT_SEARCH=^}@var{dir}. The binder generates the bind file (a C language source file) in the current working directory. @findex Ada @findex System @findex Interfaces @findex GNAT The packages @code{Ada}, @code{System}, and @code{Interfaces} and their children make up the GNAT Run-Time Library, together with the package GNAT and its children, which contain a set of useful additional library functions provided by GNAT. The sources for these units are needed by the compiler and are kept together in one directory. The ALI files and object files generated by compiling the RTL are needed by the binder and the linker and are kept together in one directory, typically different from the directory containing the sources. In a normal installation, you need not specify these directory names when compiling or binding. Either the environment variables or the built-in defaults cause these files to be found. Besides simplifying access to the RTL, a major use of search paths is in compiling sources from multiple directories. This can make development environments much more flexible. @node Examples of gnatbind Usage @section Examples of @code{gnatbind} Usage @noindent This section contains a number of examples of using the GNAT binding utility @code{gnatbind}. @table @code @item gnatbind hello The main program @code{Hello} (source program in @file{hello.adb}) is bound using the standard switch settings. The generated main program is @file{b~hello.adb}. This is the normal, default use of the binder. @ifclear vms @item gnatbind hello -o mainprog.adb @end ifclear @ifset vms @item gnatbind HELLO.ALI /OUTPUT=Mainprog.ADB @end ifset The main program @code{Hello} (source program in @file{hello.adb}) is bound using the standard switch settings. The generated main program is @file{mainprog.adb} with the associated spec in @file{mainprog.ads}. Note that you must specify the body here not the spec. Note that if this option is used, then linking must be done manually, since gnatlink will not be able to find the generated file. @end table @c ------------------------------------ @node Linking Using gnatlink @chapter Linking Using @command{gnatlink} @c ------------------------------------ @findex gnatlink @noindent This chapter discusses @command{gnatlink}, a tool that links an Ada program and builds an executable file. This utility invokes the system linker ^(via the @command{gcc} command)^^ with a correct list of object files and library references. @command{gnatlink} automatically determines the list of files and references for the Ada part of a program. It uses the binder file generated by the @command{gnatbind} to determine this list. Note: to invoke @code{gnatlink} with a project file, use the @code{gnat} driver (see @ref{The GNAT Driver and Project Files}). @menu * Running gnatlink:: * Switches for gnatlink:: @end menu @node Running gnatlink @section Running @command{gnatlink} @noindent The form of the @command{gnatlink} command is @smallexample @c $ gnatlink @ovar{switches} @var{mainprog}@r{[}.ali@r{]} @c @ovar{non-Ada objects} @ovar{linker options} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatlink @r{[}@var{switches}@r{]} @var{mainprog}@r{[}.ali@r{]} @r{[}@var{non-Ada objects}@r{]} @r{[}@var{linker options}@r{]} @end smallexample @noindent The arguments of @command{gnatlink} (switches, main @file{ALI} file, non-Ada objects or linker options) may be in any order, provided that no non-Ada object may be mistaken for a main @file{ALI} file. Any file name @file{F} without the @file{.ali} extension will be taken as the main @file{ALI} file if a file exists whose name is the concatenation of @file{F} and @file{.ali}. @noindent @file{@var{mainprog}.ali} references the ALI file of the main program. The @file{.ali} extension of this file can be omitted. From this reference, @command{gnatlink} locates the corresponding binder file @file{b~@var{mainprog}.adb} and, using the information in this file along with the list of non-Ada objects and linker options, constructs a linker command file to create the executable. The arguments other than the @command{gnatlink} switches and the main @file{ALI} file are passed to the linker uninterpreted. They typically include the names of object files for units written in other languages than Ada and any library references required to resolve references in any of these foreign language units, or in @code{Import} pragmas in any Ada units. @var{linker options} is an optional list of linker specific switches. The default linker called by gnatlink is @command{gcc} which in turn calls the appropriate system linker. Standard options for the linker such as @option{-lmy_lib} or @option{-Ldir} can be added as is. For options that are not recognized by @command{gcc} as linker options, use the @command{gcc} switches @option{-Xlinker} or @option{-Wl,}. Refer to the GCC documentation for details. Here is an example showing how to generate a linker map: @smallexample $ ^gnatlink my_prog -Wl,-Map,MAPFILE^GNAT LINK my_prog.ali /MAP^ @end smallexample Using @var{linker options} it is possible to set the program stack and heap size. @ifset unw See @ref{Setting Stack Size from gnatlink} and @ref{Setting Heap Size from gnatlink}. @end ifset @command{gnatlink} determines the list of objects required by the Ada program and prepends them to the list of objects passed to the linker. @command{gnatlink} also gathers any arguments set by the use of @code{pragma Linker_Options} and adds them to the list of arguments presented to the linker. @ifset vms @command{gnatlink} accepts the following types of extra files on the command line: objects (@file{.OBJ}), libraries (@file{.OLB}), sharable images (@file{.EXE}), and options files (@file{.OPT}). These are recognized and handled according to their extension. @end ifset @node Switches for gnatlink @section Switches for @command{gnatlink} @noindent The following switches are available with the @command{gnatlink} utility: @table @option @c !sort! @item --version @cindex @option{--version} @command{gnatlink} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatlink} If @option{--version} was not used, display usage, then exit disregarding all other options. @item ^-f^/FORCE_OBJECT_FILE_LIST^ @cindex Command line length @cindex @option{^-f^/FORCE_OBJECT_FILE_LIST^} (@command{gnatlink}) On some targets, the command line length is limited, and @command{gnatlink} will generate a separate file for the linker if the list of object files is too long. The @option{^-f^/FORCE_OBJECT_FILE_LIST^} switch forces this file to be generated even if the limit is not exceeded. This is useful in some cases to deal with special situations where the command line length is exceeded. @item ^-g^/DEBUG^ @cindex Debugging information, including @cindex @option{^-g^/DEBUG^} (@command{gnatlink}) The option to include debugging information causes the Ada bind file (in other words, @file{b~@var{mainprog}.adb}) to be compiled with @option{^-g^/DEBUG^}. In addition, the binder does not delete the @file{b~@var{mainprog}.adb}, @file{b~@var{mainprog}.o} and @file{b~@var{mainprog}.ali} files. Without @option{^-g^/DEBUG^}, the binder removes these files by default. The same procedure apply if a C bind file was generated using @option{^-C^/BIND_FILE=C^} @code{gnatbind} option, in this case the filenames are @file{b_@var{mainprog}.c} and @file{b_@var{mainprog}.o}. @item ^-n^/NOCOMPILE^ @cindex @option{^-n^/NOCOMPILE^} (@command{gnatlink}) Do not compile the file generated by the binder. This may be used when a link is rerun with different options, but there is no need to recompile the binder file. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@command{gnatlink}) Causes additional information to be output, including a full list of the included object files. This switch option is most useful when you want to see what set of object files are being used in the link step. @item ^-v -v^/VERBOSE/VERBOSE^ @cindex @option{^-v -v^/VERBOSE/VERBOSE^} (@command{gnatlink}) Very verbose mode. Requests that the compiler operate in verbose mode when it compiles the binder file, and that the system linker run in verbose mode. @item ^-o ^/EXECUTABLE=^@var{exec-name} @cindex @option{^-o^/EXECUTABLE^} (@command{gnatlink}) @var{exec-name} specifies an alternate name for the generated executable program. If this switch is omitted, the executable has the same name as the main unit. For example, @code{gnatlink try.ali} creates an executable called @file{^try^TRY.EXE^}. @ifclear vms @item -b @var{target} @cindex @option{-b} (@command{gnatlink}) Compile your program to run on @var{target}, which is the name of a system configuration. You must have a GNAT cross-compiler built if @var{target} is not the same as your host system. @item -B@var{dir} @cindex @option{-B} (@command{gnatlink}) Load compiler executables (for example, @code{gnat1}, the Ada compiler) from @var{dir} instead of the default location. Only use this switch when multiple versions of the GNAT compiler are available. @xref{Directory Options,,, gcc, The GNU Compiler Collection}, for further details. You would normally use the @option{-b} or @option{-V} switch instead. @item --GCC=@var{compiler_name} @cindex @option{--GCC=compiler_name} (@command{gnatlink}) Program used for compiling the binder file. The default is @command{gcc}. You need to use quotes around @var{compiler_name} if @code{compiler_name} contains spaces or other separator characters. As an example @option{--GCC="foo -x -y"} will instruct @command{gnatlink} to use @code{foo -x -y} as your compiler. Note that switch @option{-c} is always inserted after your command name. Thus in the above example the compiler command that will be used by @command{gnatlink} will be @code{foo -c -x -y}. A limitation of this syntax is that the name and path name of the executable itself must not include any embedded spaces. If the compiler executable is different from the default one (gcc or -gcc), then the back-end switches in the ALI file are not used to compile the binder generated source. For example, this is the case with @option{--GCC="foo -x -y"}. But the back end switches will be used for @option{--GCC="gcc -gnatv"}. If several @option{--GCC=compiler_name} are used, only the last @var{compiler_name} is taken into account. However, all the additional switches are also taken into account. Thus, @option{--GCC="foo -x -y" --GCC="bar -z -t"} is equivalent to @option{--GCC="bar -x -y -z -t"}. @item --LINK=@var{name} @cindex @option{--LINK=} (@command{gnatlink}) @var{name} is the name of the linker to be invoked. This is especially useful in mixed language programs since languages such as C++ require their own linker to be used. When this switch is omitted, the default name for the linker is @command{gcc}. When this switch is used, the specified linker is called instead of @command{gcc} with exactly the same parameters that would have been passed to @command{gcc} so if the desired linker requires different parameters it is necessary to use a wrapper script that massages the parameters before invoking the real linker. It may be useful to control the exact invocation by using the verbose switch. @end ifclear @ifset vms @item /DEBUG=TRACEBACK @cindex @code{/DEBUG=TRACEBACK} (@command{gnatlink}) This qualifier causes sufficient information to be included in the executable file to allow a traceback, but does not include the full symbol information needed by the debugger. @item /IDENTIFICATION="" @code{""} specifies the string to be stored in the image file identification field in the image header. It overrides any pragma @code{Ident} specified string. @item /NOINHIBIT-EXEC Generate the executable file even if there are linker warnings. @item /NOSTART_FILES Don't link in the object file containing the ``main'' transfer address. Used when linking with a foreign language main program compiled with an HP compiler. @item /STATIC Prefer linking with object libraries over sharable images, even without /DEBUG. @end ifset @end table @node The GNAT Make Program gnatmake @chapter The GNAT Make Program @command{gnatmake} @findex gnatmake @menu * Running gnatmake:: * Switches for gnatmake:: * Mode Switches for gnatmake:: * Notes on the Command Line:: * How gnatmake Works:: * Examples of gnatmake Usage:: @end menu @noindent A typical development cycle when working on an Ada program consists of the following steps: @enumerate @item Edit some sources to fix bugs. @item Add enhancements. @item Compile all sources affected. @item Rebind and relink. @item Test. @end enumerate @noindent The third step can be tricky, because not only do the modified files @cindex Dependency rules have to be compiled, but any files depending on these files must also be recompiled. The dependency rules in Ada can be quite complex, especially in the presence of overloading, @code{use} clauses, generics and inlined subprograms. @command{gnatmake} automatically takes care of the third and fourth steps of this process. It determines which sources need to be compiled, compiles them, and binds and links the resulting object files. Unlike some other Ada make programs, the dependencies are always accurately recomputed from the new sources. The source based approach of the GNAT compilation model makes this possible. This means that if changes to the source program cause corresponding changes in dependencies, they will always be tracked exactly correctly by @command{gnatmake}. @node Running gnatmake @section Running @command{gnatmake} @noindent The usual form of the @command{gnatmake} command is @smallexample @c $ gnatmake @ovar{switches} @var{file_name} @c @ovar{file_names} @ovar{mode_switches} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatmake @r{[}@var{switches}@r{]} @var{file_name} @r{[}@var{file_names}@r{]} @r{[}@var{mode_switches}@r{]} @end smallexample @noindent The only required argument is one @var{file_name}, which specifies a compilation unit that is a main program. Several @var{file_names} can be specified: this will result in several executables being built. If @code{switches} are present, they can be placed before the first @var{file_name}, between @var{file_names} or after the last @var{file_name}. If @var{mode_switches} are present, they must always be placed after the last @var{file_name} and all @code{switches}. If you are using standard file extensions (@file{.adb} and @file{.ads}), then the extension may be omitted from the @var{file_name} arguments. However, if you are using non-standard extensions, then it is required that the extension be given. A relative or absolute directory path can be specified in a @var{file_name}, in which case, the input source file will be searched for in the specified directory only. Otherwise, the input source file will first be searched in the directory where @command{gnatmake} was invoked and if it is not found, it will be search on the source path of the compiler as described in @ref{Search Paths and the Run-Time Library (RTL)}. All @command{gnatmake} output (except when you specify @option{^-M^/DEPENDENCIES_LIST^}) is to @file{stderr}. The output produced by the @option{^-M^/DEPENDENCIES_LIST^} switch is send to @file{stdout}. @node Switches for gnatmake @section Switches for @command{gnatmake} @noindent You may specify any of the following switches to @command{gnatmake}: @table @option @c !sort! @item --version @cindex @option{--version} @command{gnatmake} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatmake} If @option{--version} was not used, display usage, then exit disregarding all other options. @ifclear vms @item --GCC=@var{compiler_name} @cindex @option{--GCC=compiler_name} (@command{gnatmake}) Program used for compiling. The default is `@command{gcc}'. You need to use quotes around @var{compiler_name} if @code{compiler_name} contains spaces or other separator characters. As an example @option{--GCC="foo -x -y"} will instruct @command{gnatmake} to use @code{foo -x -y} as your compiler. A limitation of this syntax is that the name and path name of the executable itself must not include any embedded spaces. Note that switch @option{-c} is always inserted after your command name. Thus in the above example the compiler command that will be used by @command{gnatmake} will be @code{foo -c -x -y}. If several @option{--GCC=compiler_name} are used, only the last @var{compiler_name} is taken into account. However, all the additional switches are also taken into account. Thus, @option{--GCC="foo -x -y" --GCC="bar -z -t"} is equivalent to @option{--GCC="bar -x -y -z -t"}. @item --GNATBIND=@var{binder_name} @cindex @option{--GNATBIND=binder_name} (@command{gnatmake}) Program used for binding. The default is `@code{gnatbind}'. You need to use quotes around @var{binder_name} if @var{binder_name} contains spaces or other separator characters. As an example @option{--GNATBIND="bar -x -y"} will instruct @command{gnatmake} to use @code{bar -x -y} as your binder. Binder switches that are normally appended by @command{gnatmake} to `@code{gnatbind}' are now appended to the end of @code{bar -x -y}. A limitation of this syntax is that the name and path name of the executable itself must not include any embedded spaces. @item --GNATLINK=@var{linker_name} @cindex @option{--GNATLINK=linker_name} (@command{gnatmake}) Program used for linking. The default is `@command{gnatlink}'. You need to use quotes around @var{linker_name} if @var{linker_name} contains spaces or other separator characters. As an example @option{--GNATLINK="lan -x -y"} will instruct @command{gnatmake} to use @code{lan -x -y} as your linker. Linker switches that are normally appended by @command{gnatmake} to `@command{gnatlink}' are now appended to the end of @code{lan -x -y}. A limitation of this syntax is that the name and path name of the executable itself must not include any embedded spaces. @end ifclear @item ^--subdirs^/SUBDIRS^=subdir Actual object directory of each project file is the subdirectory subdir of the object directory specified or defaulted in the project file. @item ^--single-compile-per-obj-dir^/SINGLE_COMPILE_PER_OBJ_DIR^ Disallow simultaneous compilations in the same object directory when project files are used. @item ^--unchecked-shared-lib-imports^/UNCHECKED_SHARED_LIB_IMPORTS^ By default, shared library projects are not allowed to import static library projects. When this switch is used on the command line, this restriction is relaxed. @item ^--source-info=^/SRC_INFO=source-info-file^ Specify a source info file. This switch is active only when project files are used. If the source info file is specified as a relative path, then it is relative to the object directory of the main project. If the source info file does not exist, then after the Project Manager has successfully parsed and processed the project files and found the sources, it creates the source info file. If the source info file already exists and can be read successfully, then the Project Manager will get all the needed information about the sources from the source info file and will not look for them. This reduces the time to process the project files, especially when looking for sources that take a long time. If the source info file exists but cannot be parsed successfully, the Project Manager will attempt to recreate it. If the Project Manager fails to create the source info file, a message is issued, but gnatmake does not fail. @ifclear vms @item --create-map-file When linking an executable, create a map file. The name of the map file has the same name as the executable with extension ".map". @item --create-map-file=mapfile When linking an executable, create a map file. The name of the map file is "mapfile". @end ifclear @item ^-a^/ALL_FILES^ @cindex @option{^-a^/ALL_FILES^} (@command{gnatmake}) Consider all files in the make process, even the GNAT internal system files (for example, the predefined Ada library files), as well as any locked files. Locked files are files whose ALI file is write-protected. By default, @command{gnatmake} does not check these files, because the assumption is that the GNAT internal files are properly up to date, and also that any write protected ALI files have been properly installed. Note that if there is an installation problem, such that one of these files is not up to date, it will be properly caught by the binder. You may have to specify this switch if you are working on GNAT itself. The switch @option{^-a^/ALL_FILES^} is also useful in conjunction with @option{^-f^/FORCE_COMPILE^} if you need to recompile an entire application, including run-time files, using special configuration pragmas, such as a @code{Normalize_Scalars} pragma. By default @code{gnatmake ^-a^/ALL_FILES^} compiles all GNAT internal files with @ifclear vms @code{gcc -c -gnatpg} rather than @code{gcc -c}. @end ifclear @ifset vms the @code{/CHECKS=SUPPRESS_ALL /STYLE_CHECKS=GNAT} switch. @end ifset @item ^-b^/ACTIONS=BIND^ @cindex @option{^-b^/ACTIONS=BIND^} (@command{gnatmake}) Bind only. Can be combined with @option{^-c^/ACTIONS=COMPILE^} to do compilation and binding, but no link. Can be combined with @option{^-l^/ACTIONS=LINK^} to do binding and linking. When not combined with @option{^-c^/ACTIONS=COMPILE^} all the units in the closure of the main program must have been previously compiled and must be up to date. The root unit specified by @var{file_name} may be given without extension, with the source extension or, if no GNAT Project File is specified, with the ALI file extension. @item ^-c^/ACTIONS=COMPILE^ @cindex @option{^-c^/ACTIONS=COMPILE^} (@command{gnatmake}) Compile only. Do not perform binding, except when @option{^-b^/ACTIONS=BIND^} is also specified. Do not perform linking, except if both @option{^-b^/ACTIONS=BIND^} and @option{^-l^/ACTIONS=LINK^} are also specified. If the root unit specified by @var{file_name} is not a main unit, this is the default. Otherwise @command{gnatmake} will attempt binding and linking unless all objects are up to date and the executable is more recent than the objects. @item ^-C^/MAPPING^ @cindex @option{^-C^/MAPPING^} (@command{gnatmake}) Use a temporary mapping file. A mapping file is a way to communicate to the compiler two mappings: from unit names to file names (without any directory information) and from file names to path names (with full directory information). A mapping file can make the compiler's file searches faster, especially if there are many source directories, or the sources are read over a slow network connection. If @option{^-P^/PROJECT_FILE^} is used, a mapping file is always used, so @option{^-C^/MAPPING^} is unnecessary; in this case the mapping file is initially populated based on the project file. If @option{^-C^/MAPPING^} is used without @option{^-P^/PROJECT_FILE^}, the mapping file is initially empty. Each invocation of the compiler will add any newly accessed sources to the mapping file. @item ^-C=^/USE_MAPPING_FILE=^@var{file} @cindex @option{^-C=^/USE_MAPPING^} (@command{gnatmake}) Use a specific mapping file. The file, specified as a path name (absolute or relative) by this switch, should already exist, otherwise the switch is ineffective. The specified mapping file will be communicated to the compiler. This switch is not compatible with a project file (^-P^/PROJECT_FILE=^@var{file}) or with multiple compiling processes (^-j^/PROCESSES=^nnn, when nnn is greater than 1). @item ^-d^/DISPLAY_PROGRESS^ @cindex @option{^-d^/DISPLAY_PROGRESS^} (@command{gnatmake}) Display progress for each source, up to date or not, as a single line @smallexample completed x out of y (zz%) @end smallexample If the file needs to be compiled this is displayed after the invocation of the compiler. These lines are displayed even in quiet output mode. @item ^-D ^/DIRECTORY_OBJECTS=^@var{dir} @cindex @option{^-D^/DIRECTORY_OBJECTS^} (@command{gnatmake}) Put all object files and ALI file in directory @var{dir}. If the @option{^-D^/DIRECTORY_OBJECTS^} switch is not used, all object files and ALI files go in the current working directory. This switch cannot be used when using a project file. @ifclear vms @item -eL @cindex @option{-eL} (@command{gnatmake}) @cindex symbolic links Follow all symbolic links when processing project files. This should be used if your project uses symbolic links for files or directories, but is not needed in other cases. @cindex naming scheme This also assumes that no directory matches the naming scheme for files (for instance that you do not have a directory called "sources.ads" when using the default GNAT naming scheme). When you do not have to use this switch (ie by default), gnatmake is able to save a lot of system calls (several per source file and object file), which can result in a significant speed up to load and manipulate a project file, especially when using source files from a remote system. @end ifclear @item ^-eS^/STANDARD_OUTPUT_FOR_COMMANDS^ @cindex @option{^-eS^/STANDARD_OUTPUT_FOR_COMMANDS^} (@command{gnatmake}) Output the commands for the compiler, the binder and the linker on ^standard output^SYS$OUTPUT^, instead of ^standard error^SYS$ERROR^. @item ^-f^/FORCE_COMPILE^ @cindex @option{^-f^/FORCE_COMPILE^} (@command{gnatmake}) Force recompilations. Recompile all sources, even though some object files may be up to date, but don't recompile predefined or GNAT internal files or locked files (files with a write-protected ALI file), unless the @option{^-a^/ALL_FILES^} switch is also specified. @item ^-F^/FULL_PATH_IN_BRIEF_MESSAGES^ @cindex @option{^-F^/FULL_PATH_IN_BRIEF_MESSAGES^} (@command{gnatmake}) When using project files, if some errors or warnings are detected during parsing and verbose mode is not in effect (no use of switch ^-v^/VERBOSE^), then error lines start with the full path name of the project file, rather than its simple file name. @item ^-g^/DEBUG^ @cindex @option{^-g^/DEBUG^} (@command{gnatmake}) Enable debugging. This switch is simply passed to the compiler and to the linker. @item ^-i^/IN_PLACE^ @cindex @option{^-i^/IN_PLACE^} (@command{gnatmake}) In normal mode, @command{gnatmake} compiles all object files and ALI files into the current directory. If the @option{^-i^/IN_PLACE^} switch is used, then instead object files and ALI files that already exist are overwritten in place. This means that once a large project is organized into separate directories in the desired manner, then @command{gnatmake} will automatically maintain and update this organization. If no ALI files are found on the Ada object path (@ref{Search Paths and the Run-Time Library (RTL)}), the new object and ALI files are created in the directory containing the source being compiled. If another organization is desired, where objects and sources are kept in different directories, a useful technique is to create dummy ALI files in the desired directories. When detecting such a dummy file, @command{gnatmake} will be forced to recompile the corresponding source file, and it will be put the resulting object and ALI files in the directory where it found the dummy file. @item ^-j^/PROCESSES=^@var{n} @cindex @option{^-j^/PROCESSES^} (@command{gnatmake}) @cindex Parallel make Use @var{n} processes to carry out the (re)compilations. On a multiprocessor machine compilations will occur in parallel. In the event of compilation errors, messages from various compilations might get interspersed (but @command{gnatmake} will give you the full ordered list of failing compiles at the end). If this is problematic, rerun the make process with n set to 1 to get a clean list of messages. @item ^-k^/CONTINUE_ON_ERROR^ @cindex @option{^-k^/CONTINUE_ON_ERROR^} (@command{gnatmake}) Keep going. Continue as much as possible after a compilation error. To ease the programmer's task in case of compilation errors, the list of sources for which the compile fails is given when @command{gnatmake} terminates. If @command{gnatmake} is invoked with several @file{file_names} and with this switch, if there are compilation errors when building an executable, @command{gnatmake} will not attempt to build the following executables. @item ^-l^/ACTIONS=LINK^ @cindex @option{^-l^/ACTIONS=LINK^} (@command{gnatmake}) Link only. Can be combined with @option{^-b^/ACTIONS=BIND^} to binding and linking. Linking will not be performed if combined with @option{^-c^/ACTIONS=COMPILE^} but not with @option{^-b^/ACTIONS=BIND^}. When not combined with @option{^-b^/ACTIONS=BIND^} all the units in the closure of the main program must have been previously compiled and must be up to date, and the main program needs to have been bound. The root unit specified by @var{file_name} may be given without extension, with the source extension or, if no GNAT Project File is specified, with the ALI file extension. @item ^-m^/MINIMAL_RECOMPILATION^ @cindex @option{^-m^/MINIMAL_RECOMPILATION^} (@command{gnatmake}) Specify that the minimum necessary amount of recompilations be performed. In this mode @command{gnatmake} ignores time stamp differences when the only modifications to a source file consist in adding/removing comments, empty lines, spaces or tabs. This means that if you have changed the comments in a source file or have simply reformatted it, using this switch will tell @command{gnatmake} not to recompile files that depend on it (provided other sources on which these files depend have undergone no semantic modifications). Note that the debugging information may be out of date with respect to the sources if the @option{-m} switch causes a compilation to be switched, so the use of this switch represents a trade-off between compilation time and accurate debugging information. @item ^-M^/DEPENDENCIES_LIST^ @cindex Dependencies, producing list @cindex @option{^-M^/DEPENDENCIES_LIST^} (@command{gnatmake}) Check if all objects are up to date. If they are, output the object dependences to @file{stdout} in a form that can be directly exploited in a @file{Makefile}. By default, each source file is prefixed with its (relative or absolute) directory name. This name is whatever you specified in the various @option{^-aI^/SOURCE_SEARCH^} and @option{^-I^/SEARCH^} switches. If you use @code{gnatmake ^-M^/DEPENDENCIES_LIST^} @option{^-q^/QUIET^} (see below), only the source file names, without relative paths, are output. If you just specify the @option{^-M^/DEPENDENCIES_LIST^} switch, dependencies of the GNAT internal system files are omitted. This is typically what you want. If you also specify the @option{^-a^/ALL_FILES^} switch, dependencies of the GNAT internal files are also listed. Note that dependencies of the objects in external Ada libraries (see switch @option{^-aL^/SKIP_MISSING=^}@var{dir} in the following list) are never reported. @item ^-n^/DO_OBJECT_CHECK^ @cindex @option{^-n^/DO_OBJECT_CHECK^} (@command{gnatmake}) Don't compile, bind, or link. Checks if all objects are up to date. If they are not, the full name of the first file that needs to be recompiled is printed. Repeated use of this option, followed by compiling the indicated source file, will eventually result in recompiling all required units. @item ^-o ^/EXECUTABLE=^@var{exec_name} @cindex @option{^-o^/EXECUTABLE^} (@command{gnatmake}) Output executable name. The name of the final executable program will be @var{exec_name}. If the @option{^-o^/EXECUTABLE^} switch is omitted the default name for the executable will be the name of the input file in appropriate form for an executable file on the host system. This switch cannot be used when invoking @command{gnatmake} with several @file{file_names}. @item ^-p or --create-missing-dirs^/CREATE_MISSING_DIRS^ @cindex @option{^-p^/CREATE_MISSING_DIRS^} (@command{gnatmake}) When using project files (^-P^/PROJECT_FILE=^@var{project}), create automatically missing object directories, library directories and exec directories. @item ^-P^/PROJECT_FILE=^@var{project} @cindex @option{^-P^/PROJECT_FILE^} (@command{gnatmake}) Use project file @var{project}. Only one such switch can be used. @xref{gnatmake and Project Files}. @item ^-q^/QUIET^ @cindex @option{^-q^/QUIET^} (@command{gnatmake}) Quiet. When this flag is not set, the commands carried out by @command{gnatmake} are displayed. @item ^-s^/SWITCH_CHECK/^ @cindex @option{^-s^/SWITCH_CHECK^} (@command{gnatmake}) Recompile if compiler switches have changed since last compilation. All compiler switches but -I and -o are taken into account in the following way: orders between different ``first letter'' switches are ignored, but orders between same switches are taken into account. For example, @option{-O -O2} is different than @option{-O2 -O}, but @option{-g -O} is equivalent to @option{-O -g}. This switch is recommended when Integrated Preprocessing is used. @item ^-u^/UNIQUE^ @cindex @option{^-u^/UNIQUE^} (@command{gnatmake}) Unique. Recompile at most the main files. It implies -c. Combined with -f, it is equivalent to calling the compiler directly. Note that using ^-u^/UNIQUE^ with a project file and no main has a special meaning (@pxref{Project Files and Main Subprograms}). @item ^-U^/ALL_PROJECTS^ @cindex @option{^-U^/ALL_PROJECTS^} (@command{gnatmake}) When used without a project file or with one or several mains on the command line, is equivalent to ^-u^/UNIQUE^. When used with a project file and no main on the command line, all sources of all project files are checked and compiled if not up to date, and libraries are rebuilt, if necessary. @item ^-v^/REASONS^ @cindex @option{^-v^/REASONS^} (@command{gnatmake}) Verbose. Display the reason for all recompilations @command{gnatmake} decides are necessary, with the highest verbosity level. @item ^-vl^/LOW_VERBOSITY^ @cindex @option{^-vl^/LOW_VERBOSITY^} (@command{gnatmake}) Verbosity level Low. Display fewer lines than in verbosity Medium. @item ^-vm^/MEDIUM_VERBOSITY^ @cindex @option{^-vm^/MEDIUM_VERBOSITY^} (@command{gnatmake}) Verbosity level Medium. Potentially display fewer lines than in verbosity High. @item ^-vh^/HIGH_VERBOSITY^ @cindex @option{^-vm^/HIGH_VERBOSITY^} (@command{gnatmake}) Verbosity level High. Equivalent to ^-v^/REASONS^. @item ^-vP^/MESSAGES_PROJECT_FILE=^@emph{x} Indicate the verbosity of the parsing of GNAT project files. @xref{Switches Related to Project Files}. @item ^-x^/NON_PROJECT_UNIT_COMPILATION^ @cindex @option{^-x^/NON_PROJECT_UNIT_COMPILATION^} (@command{gnatmake}) Indicate that sources that are not part of any Project File may be compiled. Normally, when using Project Files, only sources that are part of a Project File may be compile. When this switch is used, a source outside of all Project Files may be compiled. The ALI file and the object file will be put in the object directory of the main Project. The compilation switches used will only be those specified on the command line. Even when @option{^-x^/NON_PROJECT_UNIT_COMPILATION^} is used, mains specified on the command line need to be sources of a project file. @item ^-X^/EXTERNAL_REFERENCE=^@var{name=value} Indicate that external variable @var{name} has the value @var{value}. The Project Manager will use this value for occurrences of @code{external(name)} when parsing the project file. @xref{Switches Related to Project Files}. @item ^-z^/NOMAIN^ @cindex @option{^-z^/NOMAIN^} (@command{gnatmake}) No main subprogram. Bind and link the program even if the unit name given on the command line is a package name. The resulting executable will execute the elaboration routines of the package and its closure, then the finalization routines. @end table @table @asis @item @command{gcc} @asis{switches} @ifclear vms Any uppercase or multi-character switch that is not a @command{gnatmake} switch is passed to @command{gcc} (e.g.@: @option{-O}, @option{-gnato,} etc.) @end ifclear @ifset vms Any qualifier that cannot be recognized as a qualifier for @code{GNAT MAKE} but is recognizable as a valid qualifier for @code{GNAT COMPILE} is automatically treated as a compiler switch, and passed on to all compilations that are carried out. @end ifset @end table @noindent Source and library search path switches: @table @option @c !sort! @item ^-aI^/SOURCE_SEARCH=^@var{dir} @cindex @option{^-aI^/SOURCE_SEARCH^} (@command{gnatmake}) When looking for source files also look in directory @var{dir}. The order in which source files search is undertaken is described in @ref{Search Paths and the Run-Time Library (RTL)}. @item ^-aL^/SKIP_MISSING=^@var{dir} @cindex @option{^-aL^/SKIP_MISSING^} (@command{gnatmake}) Consider @var{dir} as being an externally provided Ada library. Instructs @command{gnatmake} to skip compilation units whose @file{.ALI} files have been located in directory @var{dir}. This allows you to have missing bodies for the units in @var{dir} and to ignore out of date bodies for the same units. You still need to specify the location of the specs for these units by using the switches @option{^-aI^/SOURCE_SEARCH=^@var{dir}} or @option{^-I^/SEARCH=^@var{dir}}. Note: this switch is provided for compatibility with previous versions of @command{gnatmake}. The easier method of causing standard libraries to be excluded from consideration is to write-protect the corresponding ALI files. @item ^-aO^/OBJECT_SEARCH=^@var{dir} @cindex @option{^-aO^/OBJECT_SEARCH^} (@command{gnatmake}) When searching for library and object files, look in directory @var{dir}. The order in which library files are searched is described in @ref{Search Paths for gnatbind}. @item ^-A^/CONDITIONAL_SOURCE_SEARCH=^@var{dir} @cindex Search paths, for @command{gnatmake} @cindex @option{^-A^/CONDITIONAL_SOURCE_SEARCH^} (@command{gnatmake}) Equivalent to @option{^-aL^/SKIP_MISSING=^@var{dir} ^-aI^/SOURCE_SEARCH=^@var{dir}}. @item ^-I^/SEARCH=^@var{dir} @cindex @option{^-I^/SEARCH^} (@command{gnatmake}) Equivalent to @option{^-aO^/OBJECT_SEARCH=^@var{dir} ^-aI^/SOURCE_SEARCH=^@var{dir}}. @item ^-I-^/NOCURRENT_DIRECTORY^ @cindex @option{^-I-^/NOCURRENT_DIRECTORY^} (@command{gnatmake}) @cindex Source files, suppressing search Do not look for source files in the directory containing the source file named in the command line. Do not look for ALI or object files in the directory where @command{gnatmake} was invoked. @item ^-L^/LIBRARY_SEARCH=^@var{dir} @cindex @option{^-L^/LIBRARY_SEARCH^} (@command{gnatmake}) @cindex Linker libraries Add directory @var{dir} to the list of directories in which the linker will search for libraries. This is equivalent to @option{-largs ^-L^/LIBRARY_SEARCH=^}@var{dir}. @ifclear vms Furthermore, under Windows, the sources pointed to by the libraries path set in the registry are not searched for. @end ifclear @item -nostdinc @cindex @option{-nostdinc} (@command{gnatmake}) Do not look for source files in the system default directory. @item -nostdlib @cindex @option{-nostdlib} (@command{gnatmake}) Do not look for library files in the system default directory. @item --RTS=@var{rts-path} @cindex @option{--RTS} (@command{gnatmake}) Specifies the default location of the runtime library. GNAT looks for the runtime in the following directories, and stops as soon as a valid runtime is found (@file{adainclude} or @file{ada_source_path}, and @file{adalib} or @file{ada_object_path} present): @itemize @bullet @item /$rts_path @item /$rts_path @item /rts-$rts_path @end itemize @noindent The selected path is handled like a normal RTS path. @end table @node Mode Switches for gnatmake @section Mode Switches for @command{gnatmake} @noindent The mode switches (referred to as @code{mode_switches}) allow the inclusion of switches that are to be passed to the compiler itself, the binder or the linker. The effect of a mode switch is to cause all subsequent switches up to the end of the switch list, or up to the next mode switch, to be interpreted as switches to be passed on to the designated component of GNAT. @table @option @c !sort! @item -cargs @var{switches} @cindex @option{-cargs} (@command{gnatmake}) Compiler switches. Here @var{switches} is a list of switches that are valid switches for @command{gcc}. They will be passed on to all compile steps performed by @command{gnatmake}. @item -bargs @var{switches} @cindex @option{-bargs} (@command{gnatmake}) Binder switches. Here @var{switches} is a list of switches that are valid switches for @code{gnatbind}. They will be passed on to all bind steps performed by @command{gnatmake}. @item -largs @var{switches} @cindex @option{-largs} (@command{gnatmake}) Linker switches. Here @var{switches} is a list of switches that are valid switches for @command{gnatlink}. They will be passed on to all link steps performed by @command{gnatmake}. @item -margs @var{switches} @cindex @option{-margs} (@command{gnatmake}) Make switches. The switches are directly interpreted by @command{gnatmake}, regardless of any previous occurrence of @option{-cargs}, @option{-bargs} or @option{-largs}. @end table @node Notes on the Command Line @section Notes on the Command Line @noindent This section contains some additional useful notes on the operation of the @command{gnatmake} command. @itemize @bullet @item @cindex Recompilation, by @command{gnatmake} If @command{gnatmake} finds no ALI files, it recompiles the main program and all other units required by the main program. This means that @command{gnatmake} can be used for the initial compile, as well as during subsequent steps of the development cycle. @item If you enter @code{gnatmake @var{file}.adb}, where @file{@var{file}.adb} is a subunit or body of a generic unit, @command{gnatmake} recompiles @file{@var{file}.adb} (because it finds no ALI) and stops, issuing a warning. @item In @command{gnatmake} the switch @option{^-I^/SEARCH^} is used to specify both source and library file paths. Use @option{^-aI^/SOURCE_SEARCH^} instead if you just want to specify source paths only and @option{^-aO^/OBJECT_SEARCH^} if you want to specify library paths only. @item @command{gnatmake} will ignore any files whose ALI file is write-protected. This may conveniently be used to exclude standard libraries from consideration and in particular it means that the use of the @option{^-f^/FORCE_COMPILE^} switch will not recompile these files unless @option{^-a^/ALL_FILES^} is also specified. @item @command{gnatmake} has been designed to make the use of Ada libraries particularly convenient. Assume you have an Ada library organized as follows: @i{^obj-dir^[OBJ_DIR]^} contains the objects and ALI files for of your Ada compilation units, whereas @i{^include-dir^[INCLUDE_DIR]^} contains the specs of these units, but no bodies. Then to compile a unit stored in @code{main.adb}, which uses this Ada library you would just type @smallexample @ifclear vms $ gnatmake -aI@var{include-dir} -aL@var{obj-dir} main @end ifclear @ifset vms $ gnatmake /SOURCE_SEARCH=@i{[INCLUDE_DIR]} /SKIP_MISSING=@i{[OBJ_DIR]} main @end ifset @end smallexample @item Using @command{gnatmake} along with the @option{^-m (minimal recompilation)^/MINIMAL_RECOMPILATION^} switch provides a mechanism for avoiding unnecessary recompilations. Using this switch, you can update the comments/format of your source files without having to recompile everything. Note, however, that adding or deleting lines in a source files may render its debugging info obsolete. If the file in question is a spec, the impact is rather limited, as that debugging info will only be useful during the elaboration phase of your program. For bodies the impact can be more significant. In all events, your debugger will warn you if a source file is more recent than the corresponding object, and alert you to the fact that the debugging information may be out of date. @end itemize @node How gnatmake Works @section How @command{gnatmake} Works @noindent Generally @command{gnatmake} automatically performs all necessary recompilations and you don't need to worry about how it works. However, it may be useful to have some basic understanding of the @command{gnatmake} approach and in particular to understand how it uses the results of previous compilations without incorrectly depending on them. First a definition: an object file is considered @dfn{up to date} if the corresponding ALI file exists and if all the source files listed in the dependency section of this ALI file have time stamps matching those in the ALI file. This means that neither the source file itself nor any files that it depends on have been modified, and hence there is no need to recompile this file. @command{gnatmake} works by first checking if the specified main unit is up to date. If so, no compilations are required for the main unit. If not, @command{gnatmake} compiles the main program to build a new ALI file that reflects the latest sources. Then the ALI file of the main unit is examined to find all the source files on which the main program depends, and @command{gnatmake} recursively applies the above procedure on all these files. This process ensures that @command{gnatmake} only trusts the dependencies in an existing ALI file if they are known to be correct. Otherwise it always recompiles to determine a new, guaranteed accurate set of dependencies. As a result the program is compiled ``upside down'' from what may be more familiar as the required order of compilation in some other Ada systems. In particular, clients are compiled before the units on which they depend. The ability of GNAT to compile in any order is critical in allowing an order of compilation to be chosen that guarantees that @command{gnatmake} will recompute a correct set of new dependencies if necessary. When invoking @command{gnatmake} with several @var{file_names}, if a unit is imported by several of the executables, it will be recompiled at most once. Note: when using non-standard naming conventions (@pxref{Using Other File Names}), changing through a configuration pragmas file the version of a source and invoking @command{gnatmake} to recompile may have no effect, if the previous version of the source is still accessible by @command{gnatmake}. It may be necessary to use the switch ^-f^/FORCE_COMPILE^. @node Examples of gnatmake Usage @section Examples of @command{gnatmake} Usage @table @code @item gnatmake hello.adb Compile all files necessary to bind and link the main program @file{hello.adb} (containing unit @code{Hello}) and bind and link the resulting object files to generate an executable file @file{^hello^HELLO.EXE^}. @item gnatmake main1 main2 main3 Compile all files necessary to bind and link the main programs @file{main1.adb} (containing unit @code{Main1}), @file{main2.adb} (containing unit @code{Main2}) and @file{main3.adb} (containing unit @code{Main3}) and bind and link the resulting object files to generate three executable files @file{^main1^MAIN1.EXE^}, @file{^main2^MAIN2.EXE^} and @file{^main3^MAIN3.EXE^}. @ifclear vms @item gnatmake -q Main_Unit -cargs -O2 -bargs -l @end ifclear @ifset vms @item gnatmake Main_Unit /QUIET /COMPILER_QUALIFIERS /OPTIMIZE=ALL /BINDER_QUALIFIERS /ORDER_OF_ELABORATION @end ifset Compile all files necessary to bind and link the main program unit @code{Main_Unit} (from file @file{main_unit.adb}). All compilations will be done with optimization level 2 and the order of elaboration will be listed by the binder. @command{gnatmake} will operate in quiet mode, not displaying commands it is executing. @end table @c ************************* @node Improving Performance @chapter Improving Performance @cindex Improving performance @noindent This chapter presents several topics related to program performance. It first describes some of the tradeoffs that need to be considered and some of the techniques for making your program run faster. It then documents the @command{gnatelim} tool and unused subprogram/data elimination feature, which can reduce the size of program executables. Note: to invoke @command{gnatelim} with a project file, use the @code{gnat} driver (see @ref{The GNAT Driver and Project Files}). @ifnottex @menu * Performance Considerations:: * Text_IO Suggestions:: * Reducing Size of Ada Executables with gnatelim:: * Reducing Size of Executables with unused subprogram/data elimination:: @end menu @end ifnottex @c ***************************** @node Performance Considerations @section Performance Considerations @noindent The GNAT system provides a number of options that allow a trade-off between @itemize @bullet @item performance of the generated code @item speed of compilation @item minimization of dependences and recompilation @item the degree of run-time checking. @end itemize @noindent The defaults (if no options are selected) aim at improving the speed of compilation and minimizing dependences, at the expense of performance of the generated code: @itemize @bullet @item no optimization @item no inlining of subprogram calls @item all run-time checks enabled except overflow and elaboration checks @end itemize @noindent These options are suitable for most program development purposes. This chapter describes how you can modify these choices, and also provides some guidelines on debugging optimized code. @menu * Controlling Run-Time Checks:: * Use of Restrictions:: * Optimization Levels:: * Debugging Optimized Code:: * Inlining of Subprograms:: * Other Optimization Switches:: * Optimization and Strict Aliasing:: @ifset vms * Coverage Analysis:: @end ifset @end menu @node Controlling Run-Time Checks @subsection Controlling Run-Time Checks @noindent By default, GNAT generates all run-time checks, except integer overflow checks, stack overflow checks, and checks for access before elaboration on subprogram calls. The latter are not required in default mode, because all necessary checking is done at compile time. @cindex @option{-gnatp} (@command{gcc}) @cindex @option{-gnato} (@command{gcc}) Two gnat switches, @option{-gnatp} and @option{-gnato} allow this default to be modified. @xref{Run-Time Checks}. Our experience is that the default is suitable for most development purposes. We treat integer overflow specially because these are quite expensive and in our experience are not as important as other run-time checks in the development process. Note that division by zero is not considered an overflow check, and divide by zero checks are generated where required by default. Elaboration checks are off by default, and also not needed by default, since GNAT uses a static elaboration analysis approach that avoids the need for run-time checking. This manual contains a full chapter discussing the issue of elaboration checks, and if the default is not satisfactory for your use, you should read this chapter. For validity checks, the minimal checks required by the Ada Reference Manual (for case statements and assignments to array elements) are on by default. These can be suppressed by use of the @option{-gnatVn} switch. Note that in Ada 83, there were no validity checks, so if the Ada 83 mode is acceptable (or when comparing GNAT performance with an Ada 83 compiler), it may be reasonable to routinely use @option{-gnatVn}. Validity checks are also suppressed entirely if @option{-gnatp} is used. @cindex Overflow checks @cindex Checks, overflow @findex Suppress @findex Unsuppress @cindex pragma Suppress @cindex pragma Unsuppress Note that the setting of the switches controls the default setting of the checks. They may be modified using either @code{pragma Suppress} (to remove checks) or @code{pragma Unsuppress} (to add back suppressed checks) in the program source. @node Use of Restrictions @subsection Use of Restrictions @noindent The use of pragma Restrictions allows you to control which features are permitted in your program. Apart from the obvious point that if you avoid relatively expensive features like finalization (enforceable by the use of pragma Restrictions (No_Finalization), the use of this pragma does not affect the generated code in most cases. One notable exception to this rule is that the possibility of task abort results in some distributed overhead, particularly if finalization or exception handlers are used. The reason is that certain sections of code have to be marked as non-abortable. If you use neither the @code{abort} statement, nor asynchronous transfer of control (@code{select @dots{} then abort}), then this distributed overhead is removed, which may have a general positive effect in improving overall performance. Especially code involving frequent use of tasking constructs and controlled types will show much improved performance. The relevant restrictions pragmas are @smallexample @c ada pragma Restrictions (No_Abort_Statements); pragma Restrictions (Max_Asynchronous_Select_Nesting => 0); @end smallexample @noindent It is recommended that these restriction pragmas be used if possible. Note that this also means that you can write code without worrying about the possibility of an immediate abort at any point. @node Optimization Levels @subsection Optimization Levels @cindex @option{^-O^/OPTIMIZE^} (@command{gcc}) @noindent Without any optimization ^option,^qualifier,^ the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the subprogram and get exactly the results you would expect from the source code. Turning on optimization makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program. If you use multiple ^-O options, with or without level numbers,^/OPTIMIZE qualifiers,^ the last such option is the one that is effective. @noindent The default is optimization off. This results in the fastest compile times, but GNAT makes absolutely no attempt to optimize, and the generated programs are considerably larger and slower than when optimization is enabled. You can use the @ifclear vms @option{-O} switch (the permitted forms are @option{-O0}, @option{-O1} @option{-O2}, @option{-O3}, and @option{-Os}) @end ifclear @ifset vms @code{OPTIMIZE} qualifier @end ifset to @command{gcc} to control the optimization level: @table @option @item ^-O0^/OPTIMIZE=NONE^ No optimization (the default); generates unoptimized code but has the fastest compilation time. Note that many other compilers do fairly extensive optimization even if ``no optimization'' is specified. With gcc, it is very unusual to use ^-O0^/OPTIMIZE=NONE^ for production if execution time is of any concern, since ^-O0^/OPTIMIZE=NONE^ really does mean no optimization at all. This difference between gcc and other compilers should be kept in mind when doing performance comparisons. @item ^-O1^/OPTIMIZE=SOME^ Moderate optimization; optimizes reasonably well but does not degrade compilation time significantly. @item ^-O2^/OPTIMIZE=ALL^ @ifset vms @itemx /OPTIMIZE=DEVELOPMENT @end ifset Full optimization; generates highly optimized code and has the slowest compilation time. @item ^-O3^/OPTIMIZE=INLINING^ Full optimization as in @option{-O2}; also uses more aggressive automatic inlining of subprograms within a unit (@pxref{Inlining of Subprograms}) and attemps to vectorize loops. @item ^-Os^/OPTIMIZE=SPACE^ Optimize space usage (code and data) of resulting program. @end table @noindent Higher optimization levels perform more global transformations on the program and apply more expensive analysis algorithms in order to generate faster and more compact code. The price in compilation time, and the resulting improvement in execution time, both depend on the particular application and the hardware environment. You should experiment to find the best level for your application. Since the precise set of optimizations done at each level will vary from release to release (and sometime from target to target), it is best to think of the optimization settings in general terms. @xref{Optimize Options,, Options That Control Optimization, gcc, Using the GNU Compiler Collection (GCC)}, for details about ^the @option{-O} settings and a number of @option{-f} options that^how to^ individually enable or disable specific optimizations. Unlike some other compilation systems, ^@command{gcc}^GNAT^ has been tested extensively at all optimization levels. There are some bugs which appear only with optimization turned on, but there have also been bugs which show up only in @emph{unoptimized} code. Selecting a lower level of optimization does not improve the reliability of the code generator, which in practice is highly reliable at all optimization levels. Note regarding the use of @option{-O3}: The use of this optimization level is generally discouraged with GNAT, since it often results in larger executables which may run more slowly. See further discussion of this point in @ref{Inlining of Subprograms}. @node Debugging Optimized Code @subsection Debugging Optimized Code @cindex Debugging optimized code @cindex Optimization and debugging @noindent Although it is possible to do a reasonable amount of debugging at @ifclear vms nonzero optimization levels, the higher the level the more likely that @end ifclear @ifset vms @option{/OPTIMIZE} settings other than @code{NONE}, such settings will make it more likely that @end ifset source-level constructs will have been eliminated by optimization. For example, if a loop is strength-reduced, the loop control variable may be completely eliminated and thus cannot be displayed in the debugger. This can only happen at @option{-O2} or @option{-O3}. Explicit temporary variables that you code might be eliminated at ^level^setting^ @option{-O1} or higher. The use of the @option{^-g^/DEBUG^} switch, @cindex @option{^-g^/DEBUG^} (@command{gcc}) which is needed for source-level debugging, affects the size of the program executable on disk, and indeed the debugging information can be quite large. However, it has no effect on the generated code (and thus does not degrade performance) Since the compiler generates debugging tables for a compilation unit before it performs optimizations, the optimizing transformations may invalidate some of the debugging data. You therefore need to anticipate certain anomalous situations that may arise while debugging optimized code. These are the most common cases: @enumerate @item @i{The ``hopping Program Counter'':} Repeated @code{step} or @code{next} commands show the PC bouncing back and forth in the code. This may result from any of the following optimizations: @itemize @bullet @item @i{Common subexpression elimination:} using a single instance of code for a quantity that the source computes several times. As a result you may not be able to stop on what looks like a statement. @item @i{Invariant code motion:} moving an expression that does not change within a loop, to the beginning of the loop. @item @i{Instruction scheduling:} moving instructions so as to overlap loads and stores (typically) with other code, or in general to move computations of values closer to their uses. Often this causes you to pass an assignment statement without the assignment happening and then later bounce back to the statement when the value is actually needed. Placing a breakpoint on a line of code and then stepping over it may, therefore, not always cause all the expected side-effects. @end itemize @item @i{The ``big leap'':} More commonly known as @emph{cross-jumping}, in which two identical pieces of code are merged and the program counter suddenly jumps to a statement that is not supposed to be executed, simply because it (and the code following) translates to the same thing as the code that @emph{was} supposed to be executed. This effect is typically seen in sequences that end in a jump, such as a @code{goto}, a @code{return}, or a @code{break} in a C @code{^switch^switch^} statement. @item @i{The ``roving variable'':} The symptom is an unexpected value in a variable. There are various reasons for this effect: @itemize @bullet @item In a subprogram prologue, a parameter may not yet have been moved to its ``home''. @item A variable may be dead, and its register re-used. This is probably the most common cause. @item As mentioned above, the assignment of a value to a variable may have been moved. @item A variable may be eliminated entirely by value propagation or other means. In this case, GCC may incorrectly generate debugging information for the variable @end itemize @noindent In general, when an unexpected value appears for a local variable or parameter you should first ascertain if that value was actually computed by your program, as opposed to being incorrectly reported by the debugger. Record fields or array elements in an object designated by an access value are generally less of a problem, once you have ascertained that the access value is sensible. Typically, this means checking variables in the preceding code and in the calling subprogram to verify that the value observed is explainable from other values (one must apply the procedure recursively to those other values); or re-running the code and stopping a little earlier (perhaps before the call) and stepping to better see how the variable obtained the value in question; or continuing to step @emph{from} the point of the strange value to see if code motion had simply moved the variable's assignments later. @end enumerate @noindent In light of such anomalies, a recommended technique is to use @option{-O0} early in the software development cycle, when extensive debugging capabilities are most needed, and then move to @option{-O1} and later @option{-O2} as the debugger becomes less critical. Whether to use the @option{^-g^/DEBUG^} switch in the release version is a release management issue. @ifclear vms Note that if you use @option{-g} you can then use the @command{strip} program on the resulting executable, which removes both debugging information and global symbols. @end ifclear @node Inlining of Subprograms @subsection Inlining of Subprograms @noindent A call to a subprogram in the current unit is inlined if all the following conditions are met: @itemize @bullet @item The optimization level is at least @option{-O1}. @item The called subprogram is suitable for inlining: It must be small enough and not contain something that @command{gcc} cannot support in inlined subprograms. @item @cindex pragma Inline @findex Inline Either @code{pragma Inline} applies to the subprogram and the @option{^-gnatn^/INLINE^} switch is used on the command line, or it is local to the unit and called once from within it, or it is small and optimization level @option{-O2} is specified, or automatic inlining (optimization level @option{-O3}) is specified. @end itemize @noindent Calls to subprograms in @code{with}'ed units are normally not inlined. To achieve actual inlining (that is, replacement of the call by the code in the body of the subprogram), the following conditions must all be true. @itemize @bullet @item The optimization level is at least @option{-O1}. @item The called subprogram is suitable for inlining: It must be small enough and not contain something that @command{gcc} cannot support in inlined subprograms. @item The call appears in a body (not in a package spec). @item There is a @code{pragma Inline} for the subprogram. @item The @option{^-gnatn^/INLINE^} switch is used on the command line. @end itemize Even if all these conditions are met, it may not be possible for the compiler to inline the call, due to the length of the body, or features in the body that make it impossible for the compiler to do the inlining. Note that specifying the @option{-gnatn} switch causes additional compilation dependencies. Consider the following: @smallexample @c ada @cartouche package R is procedure Q; pragma Inline (Q); end R; package body R is @dots{} end R; with R; procedure Main is begin @dots{} R.Q; end Main; @end cartouche @end smallexample @noindent With the default behavior (no @option{-gnatn} switch specified), the compilation of the @code{Main} procedure depends only on its own source, @file{main.adb}, and the spec of the package in file @file{r.ads}. This means that editing the body of @code{R} does not require recompiling @code{Main}. On the other hand, the call @code{R.Q} is not inlined under these circumstances. If the @option{-gnatn} switch is present when @code{Main} is compiled, the call will be inlined if the body of @code{Q} is small enough, but now @code{Main} depends on the body of @code{R} in @file{r.adb} as well as on the spec. This means that if this body is edited, the main program must be recompiled. Note that this extra dependency occurs whether or not the call is in fact inlined by @command{gcc}. The use of front end inlining with @option{-gnatN} generates similar additional dependencies. @cindex @option{^-fno-inline^/INLINE=SUPPRESS^} (@command{gcc}) Note: The @option{^-fno-inline^/INLINE=SUPPRESS^} switch can be used to prevent all inlining. This switch overrides all other conditions and ensures that no inlining occurs. The extra dependences resulting from @option{-gnatn} will still be active, even if this switch is used to suppress the resulting inlining actions. @cindex @option{-fno-inline-functions} (@command{gcc}) Note: The @option{-fno-inline-functions} switch can be used to prevent automatic inlining of subprograms if @option{-O3} is used. @cindex @option{-fno-inline-small-functions} (@command{gcc}) Note: The @option{-fno-inline-small-functions} switch can be used to prevent automatic inlining of small subprograms if @option{-O2} is used. @cindex @option{-fno-inline-functions-called-once} (@command{gcc}) Note: The @option{-fno-inline-functions-called-once} switch can be used to prevent inlining of subprograms local to the unit and called once from within it if @option{-O1} is used. Note regarding the use of @option{-O3}: There is no difference in inlining behavior between @option{-O2} and @option{-O3} for subprograms with an explicit pragma @code{Inline} assuming the use of @option{-gnatn} or @option{-gnatN} (the switches that activate inlining). If you have used pragma @code{Inline} in appropriate cases, then it is usually much better to use @option{-O2} and @option{-gnatn} and avoid the use of @option{-O3} which in this case only has the effect of inlining subprograms you did not think should be inlined. We often find that the use of @option{-O3} slows down code by performing excessive inlining, leading to increased instruction cache pressure from the increased code size. So the bottom line here is that you should not automatically assume that @option{-O3} is better than @option{-O2}, and indeed you should use @option{-O3} only if tests show that it actually improves performance. @node Other Optimization Switches @subsection Other Optimization Switches @cindex Optimization Switches Since @code{GNAT} uses the @command{gcc} back end, all the specialized @command{gcc} optimization switches are potentially usable. These switches have not been extensively tested with GNAT but can generally be expected to work. Examples of switches in this category are @option{-funroll-loops} and the various target-specific @option{-m} options (in particular, it has been observed that @option{-march=pentium4} can significantly improve performance on appropriate machines). For full details of these switches, see @ref{Submodel Options,, Hardware Models and Configurations, gcc, Using the GNU Compiler Collection (GCC)}. @node Optimization and Strict Aliasing @subsection Optimization and Strict Aliasing @cindex Aliasing @cindex Strict Aliasing @cindex No_Strict_Aliasing @noindent The strong typing capabilities of Ada allow an optimizer to generate efficient code in situations where other languages would be forced to make worst case assumptions preventing such optimizations. Consider the following example: @smallexample @c ada @cartouche procedure R is type Int1 is new Integer; type Int2 is new Integer; type Int1A is access Int1; type Int2A is access Int2; Int1V : Int1A; Int2V : Int2A; @dots{} begin @dots{} for J in Data'Range loop if Data (J) = Int1V.all then Int2V.all := Int2V.all + 1; end if; end loop; @dots{} end R; @end cartouche @end smallexample @noindent In this example, since the variable @code{Int1V} can only access objects of type @code{Int1}, and @code{Int2V} can only access objects of type @code{Int2}, there is no possibility that the assignment to @code{Int2V.all} affects the value of @code{Int1V.all}. This means that the compiler optimizer can "know" that the value @code{Int1V.all} is constant for all iterations of the loop and avoid the extra memory reference required to dereference it each time through the loop. This kind of optimization, called strict aliasing analysis, is triggered by specifying an optimization level of @option{-O2} or higher or @option{-Os} and allows @code{GNAT} to generate more efficient code when access values are involved. However, although this optimization is always correct in terms of the formal semantics of the Ada Reference Manual, difficulties can arise if features like @code{Unchecked_Conversion} are used to break the typing system. Consider the following complete program example: @smallexample @c ada @cartouche package p1 is type int1 is new integer; type int2 is new integer; type a1 is access int1; type a2 is access int2; end p1; with p1; use p1; package p2 is function to_a2 (Input : a1) return a2; end p2; with Unchecked_Conversion; package body p2 is function to_a2 (Input : a1) return a2 is function to_a2u is new Unchecked_Conversion (a1, a2); begin return to_a2u (Input); end to_a2; end p2; with p2; use p2; with p1; use p1; with Text_IO; use Text_IO; procedure m is v1 : a1 := new int1; v2 : a2 := to_a2 (v1); begin v1.all := 1; v2.all := 0; put_line (int1'image (v1.all)); end; @end cartouche @end smallexample @noindent This program prints out 0 in @option{-O0} or @option{-O1} mode, but it prints out 1 in @option{-O2} mode. That's because in strict aliasing mode, the compiler can and does assume that the assignment to @code{v2.all} could not affect the value of @code{v1.all}, since different types are involved. This behavior is not a case of non-conformance with the standard, since the Ada RM specifies that an unchecked conversion where the resulting bit pattern is not a correct value of the target type can result in an abnormal value and attempting to reference an abnormal value makes the execution of a program erroneous. That's the case here since the result does not point to an object of type @code{int2}. This means that the effect is entirely unpredictable. However, although that explanation may satisfy a language lawyer, in practice an applications programmer expects an unchecked conversion involving pointers to create true aliases and the behavior of printing 1 seems plain wrong. In this case, the strict aliasing optimization is unwelcome. Indeed the compiler recognizes this possibility, and the unchecked conversion generates a warning: @smallexample p2.adb:5:07: warning: possible aliasing problem with type "a2" p2.adb:5:07: warning: use -fno-strict-aliasing switch for references p2.adb:5:07: warning: or use "pragma No_Strict_Aliasing (a2);" @end smallexample @noindent Unfortunately the problem is recognized when compiling the body of package @code{p2}, but the actual "bad" code is generated while compiling the body of @code{m} and this latter compilation does not see the suspicious @code{Unchecked_Conversion}. As implied by the warning message, there are approaches you can use to avoid the unwanted strict aliasing optimization in a case like this. One possibility is to simply avoid the use of @option{-O2}, but that is a bit drastic, since it throws away a number of useful optimizations that do not involve strict aliasing assumptions. A less drastic approach is to compile the program using the option @option{-fno-strict-aliasing}. Actually it is only the unit containing the dereferencing of the suspicious pointer that needs to be compiled. So in this case, if we compile unit @code{m} with this switch, then we get the expected value of zero printed. Analyzing which units might need the switch can be painful, so a more reasonable approach is to compile the entire program with options @option{-O2} and @option{-fno-strict-aliasing}. If the performance is satisfactory with this combination of options, then the advantage is that the entire issue of possible "wrong" optimization due to strict aliasing is avoided. To avoid the use of compiler switches, the configuration pragma @code{No_Strict_Aliasing} with no parameters may be used to specify that for all access types, the strict aliasing optimization should be suppressed. However, these approaches are still overkill, in that they causes all manipulations of all access values to be deoptimized. A more refined approach is to concentrate attention on the specific access type identified as problematic. First, if a careful analysis of uses of the pointer shows that there are no possible problematic references, then the warning can be suppressed by bracketing the instantiation of @code{Unchecked_Conversion} to turn the warning off: @smallexample @c ada pragma Warnings (Off); function to_a2u is new Unchecked_Conversion (a1, a2); pragma Warnings (On); @end smallexample @noindent Of course that approach is not appropriate for this particular example, since indeed there is a problematic reference. In this case we can take one of two other approaches. The first possibility is to move the instantiation of unchecked conversion to the unit in which the type is declared. In this example, we would move the instantiation of @code{Unchecked_Conversion} from the body of package @code{p2} to the spec of package @code{p1}. Now the warning disappears. That's because any use of the access type knows there is a suspicious unchecked conversion, and the strict aliasing optimization is automatically suppressed for the type. If it is not practical to move the unchecked conversion to the same unit in which the destination access type is declared (perhaps because the source type is not visible in that unit), you may use pragma @code{No_Strict_Aliasing} for the type. This pragma must occur in the same declarative sequence as the declaration of the access type: @smallexample @c ada type a2 is access int2; pragma No_Strict_Aliasing (a2); @end smallexample @noindent Here again, the compiler now knows that the strict aliasing optimization should be suppressed for any reference to type @code{a2} and the expected behavior is obtained. Finally, note that although the compiler can generate warnings for simple cases of unchecked conversions, there are tricker and more indirect ways of creating type incorrect aliases which the compiler cannot detect. Examples are the use of address overlays and unchecked conversions involving composite types containing access types as components. In such cases, no warnings are generated, but there can still be aliasing problems. One safe coding practice is to forbid the use of address clauses for type overlaying, and to allow unchecked conversion only for primitive types. This is not really a significant restriction since any possible desired effect can be achieved by unchecked conversion of access values. The aliasing analysis done in strict aliasing mode can certainly have significant benefits. We have seen cases of large scale application code where the time is increased by up to 5% by turning this optimization off. If you have code that includes significant usage of unchecked conversion, you might want to just stick with @option{-O1} and avoid the entire issue. If you get adequate performance at this level of optimization level, that's probably the safest approach. If tests show that you really need higher levels of optimization, then you can experiment with @option{-O2} and @option{-O2 -fno-strict-aliasing} to see how much effect this has on size and speed of the code. If you really need to use @option{-O2} with strict aliasing in effect, then you should review any uses of unchecked conversion of access types, particularly if you are getting the warnings described above. @ifset vms @node Coverage Analysis @subsection Coverage Analysis @noindent GNAT supports the HP Performance Coverage Analyzer (PCA), which allows the user to determine the distribution of execution time across a program, @pxref{Profiling} for details of usage. @end ifset @node Text_IO Suggestions @section @code{Text_IO} Suggestions @cindex @code{Text_IO} and performance @noindent The @code{Ada.Text_IO} package has fairly high overheads due in part to the requirement of maintaining page and line counts. If performance is critical, a recommendation is to use @code{Stream_IO} instead of @code{Text_IO} for volume output, since this package has less overhead. If @code{Text_IO} must be used, note that by default output to the standard output and standard error files is unbuffered (this provides better behavior when output statements are used for debugging, or if the progress of a program is observed by tracking the output, e.g. by using the Unix @command{tail -f} command to watch redirected output. If you are generating large volumes of output with @code{Text_IO} and performance is an important factor, use a designated file instead of the standard output file, or change the standard output file to be buffered using @code{Interfaces.C_Streams.setvbuf}. @node Reducing Size of Ada Executables with gnatelim @section Reducing Size of Ada Executables with @code{gnatelim} @findex gnatelim @noindent This section describes @command{gnatelim}, a tool which detects unused subprograms and helps the compiler to create a smaller executable for your program. @menu * About gnatelim:: * Running gnatelim:: * Processing Precompiled Libraries:: * Correcting the List of Eliminate Pragmas:: * Making Your Executables Smaller:: * Summary of the gnatelim Usage Cycle:: @end menu @node About gnatelim @subsection About @code{gnatelim} @noindent When a program shares a set of Ada packages with other programs, it may happen that this program uses only a fraction of the subprograms defined in these packages. The code created for these unused subprograms increases the size of the executable. @code{gnatelim} tracks unused subprograms in an Ada program and outputs a list of GNAT-specific pragmas @code{Eliminate} marking all the subprograms that are declared but never called. By placing the list of @code{Eliminate} pragmas in the GNAT configuration file @file{gnat.adc} and recompiling your program, you may decrease the size of its executable, because the compiler will not generate the code for 'eliminated' subprograms. @xref{Pragma Eliminate,,, gnat_rm, GNAT Reference Manual}, for more information about this pragma. @code{gnatelim} needs as its input data the name of the main subprogram. If a set of source files is specified as @code{gnatelim} arguments, it treats these files as a complete set of sources making up a program to analyse, and analyses only these sources. After a full successful build of the main subprogram @code{gnatelim} can be called without specifying sources to analyse, in this case it computes the source closure of the main unit from the @file{ALI} files. The following command will create the set of @file{ALI} files needed for @code{gnatelim}: @smallexample $ gnatmake ^-c Main_Prog^/ACTIONS=COMPILE MAIN_PROG^ @end smallexample Note that @code{gnatelim} does not need object files. @node Running gnatelim @subsection Running @code{gnatelim} @noindent @code{gnatelim} has the following command-line interface: @smallexample $ gnatelim [@var{switches}] ^-main^?MAIN^=@var{main_unit_name} @{@var{filename}@} @r{[}-cargs @var{gcc_switches}@r{]} @end smallexample @noindent @var{main_unit_name} should be a name of a source file that contains the main subprogram of a program (partition). Each @var{filename} is the name (including the extension) of a source file to process. ``Wildcards'' are allowed, and the file name may contain path information. @samp{@var{gcc_switches}} is a list of switches for @command{gcc}. They will be passed on to all compiler invocations made by @command{gnatelim} to generate the ASIS trees. Here you can provide @option{^-I^/INCLUDE_DIRS=^} switches to form the source search path, use the @option{-gnatec} switch to set the configuration file, use the @option{-gnat05} switch if sources should be compiled in Ada 2005 mode etc. @code{gnatelim} has the following switches: @table @option @c !sort! @item ^-files^/FILES^=@var{filename} @cindex @option{^-files^/FILES^} (@code{gnatelim}) Take the argument source files from the specified file. This file should be an ordinary text file containing file names separated by spaces or line breaks. You can use this switch more than once in the same call to @command{gnatelim}. You also can combine this switch with an explicit list of files. @item ^-log^/LOG^ @cindex @option{^-log^/LOG^} (@command{gnatelim}) Duplicate all the output sent to @file{stderr} into a log file. The log file is named @file{gnatelim.log} and is located in the current directory. @item ^-log^/LOGFILE^=@var{filename} @cindex @option{^-log^/LOGFILE^} (@command{gnatelim}) Duplicate all the output sent to @file{stderr} into a specified log file. @cindex @option{^--no-elim-dispatch^/NO_DISPATCH^} (@command{gnatelim}) @item ^--no-elim-dispatch^/NO_DISPATCH^ Do not generate pragmas for dispatching operations. @cindex @option{^-o^/OUTPUT^} (@command{gnatelim}) @item ^-o^/OUTPUT^=@var{report_file} Put @command{gnatelim} output into a specified file. If this file already exists, it is overridden. If this switch is not used, @command{gnatelim} outputs its results into @file{stderr} @item ^-q^/QUIET^ @cindex @option{^-q^/QUIET^} (@command{gnatelim}) Quiet mode: by default @code{gnatelim} outputs to the standard error stream the number of program units left to be processed. This option turns this trace off. @cindex @option{^-t^/TIME^} (@command{gnatelim}) @item ^-t^/TIME^ Print out execution time. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@command{gnatelim}) Verbose mode: @code{gnatelim} version information is printed as Ada comments to the standard output stream. Also, in addition to the number of program units left @code{gnatelim} will output the name of the current unit being processed. @item ^-wq^/WARNINGS=QUIET^ @cindex @option{^-wq^/WARNINGS=QUIET^} (@command{gnatelim}) Quet warning mode - some warnings are suppressed. In particular warnings that indicate that the analysed set of sources is incomplete to make up a partition and that some subprogram bodies are missing are not generated. @end table @node Processing Precompiled Libraries @subsection Processing Precompiled Libraries @noindent If some program uses a precompiled Ada library, it can be processed by @code{gnatelim} in a usual way. @code{gnatelim} will newer generate an Eliminate pragma for a subprogram if the body of this subprogram has not been analysed, this is a typical case for subprograms from precompiled libraries. Switch @option{^-wq^/WARNINGS=QUIET^} may be used to suppress warnings about missing source files and non-analyzed subprogram bodies that can be generated when processing precompiled Ada libraries. @node Correcting the List of Eliminate Pragmas @subsection Correcting the List of Eliminate Pragmas @noindent In some rare cases @code{gnatelim} may try to eliminate subprograms that are actually called in the program. In this case, the compiler will generate an error message of the form: @smallexample main.adb:4:08: cannot reference subprogram "P" eliminated at elim.out:5 @end smallexample @noindent You will need to manually remove the wrong @code{Eliminate} pragmas from the configuration file indicated in the error message. You should recompile your program from scratch after that, because you need a consistent configuration file(s) during the entire compilation. @node Making Your Executables Smaller @subsection Making Your Executables Smaller @noindent In order to get a smaller executable for your program you now have to recompile the program completely with the configuration file containing pragmas Eliminate generated by gnatelim. If these pragmas are placed in @file{gnat.adc} file located in your current directory, just do: @smallexample $ gnatmake ^-f main_prog^/FORCE_COMPILE MAIN_PROG^ @end smallexample @noindent (Use the @option{^-f^/FORCE_COMPILE^} option for @command{gnatmake} to recompile everything with the set of pragmas @code{Eliminate} that you have obtained with @command{gnatelim}). Be aware that the set of @code{Eliminate} pragmas is specific to each program. It is not recommended to merge sets of @code{Eliminate} pragmas created for different programs in one configuration file. @node Summary of the gnatelim Usage Cycle @subsection Summary of the @code{gnatelim} Usage Cycle @noindent Here is a quick summary of the steps to be taken in order to reduce the size of your executables with @code{gnatelim}. You may use other GNAT options to control the optimization level, to produce the debugging information, to set search path, etc. @enumerate @item Create a complete set of @file{ALI} files (if the program has not been built already) @smallexample $ gnatmake ^-c main_prog^/ACTIONS=COMPILE MAIN_PROG^ @end smallexample @item Generate a list of @code{Eliminate} pragmas in default configuration file @file{gnat.adc} in the current directory @smallexample @ifset vms $ PIPE GNAT ELIM MAIN_PROG > GNAT.ADC @end ifset @ifclear vms $ gnatelim main_prog >@r{[}>@r{]} gnat.adc @end ifclear @end smallexample @item Recompile the application @smallexample $ gnatmake ^-f main_prog^/FORCE_COMPILE MAIN_PROG^ @end smallexample @end enumerate @node Reducing Size of Executables with unused subprogram/data elimination @section Reducing Size of Executables with Unused Subprogram/Data Elimination @findex unused subprogram/data elimination @noindent This section describes how you can eliminate unused subprograms and data from your executable just by setting options at compilation time. @menu * About unused subprogram/data elimination:: * Compilation options:: * Example of unused subprogram/data elimination:: @end menu @node About unused subprogram/data elimination @subsection About unused subprogram/data elimination @noindent By default, an executable contains all code and data of its composing objects (directly linked or coming from statically linked libraries), even data or code never used by this executable. This feature will allow you to eliminate such unused code from your executable, making it smaller (in disk and in memory). This functionality is available on all Linux platforms except for the IA-64 architecture and on all cross platforms using the ELF binary file format. In both cases GNU binutils version 2.16 or later are required to enable it. @node Compilation options @subsection Compilation options @noindent The operation of eliminating the unused code and data from the final executable is directly performed by the linker. In order to do this, it has to work with objects compiled with the following options: @option{-ffunction-sections} @option{-fdata-sections}. @cindex @option{-ffunction-sections} (@command{gcc}) @cindex @option{-fdata-sections} (@command{gcc}) These options are usable with C and Ada files. They will place respectively each function or data in a separate section in the resulting object file. Once the objects and static libraries are created with these options, the linker can perform the dead code elimination. You can do this by setting the @option{-Wl,--gc-sections} option to gcc command or in the @option{-largs} section of @command{gnatmake}. This will perform a garbage collection of code and data never referenced. If the linker performs a partial link (@option{-r} ld linker option), then you will need to provide one or several entry point using the @option{-e} / @option{--entry} ld option. Note that objects compiled without the @option{-ffunction-sections} and @option{-fdata-sections} options can still be linked with the executable. However, no dead code elimination will be performed on those objects (they will be linked as is). The GNAT static library is now compiled with -ffunction-sections and -fdata-sections on some platforms. This allows you to eliminate the unused code and data of the GNAT library from your executable. @node Example of unused subprogram/data elimination @subsection Example of unused subprogram/data elimination @noindent Here is a simple example: @smallexample @c ada with Aux; procedure Test is begin Aux.Used (10); end Test; package Aux is Used_Data : Integer; Unused_Data : Integer; procedure Used (Data : Integer); procedure Unused (Data : Integer); end Aux; package body Aux is procedure Used (Data : Integer) is begin Used_Data := Data; end Used; procedure Unused (Data : Integer) is begin Unused_Data := Data; end Unused; end Aux; @end smallexample @noindent @code{Unused} and @code{Unused_Data} are never referenced in this code excerpt, and hence they may be safely removed from the final executable. @smallexample $ gnatmake test $ nm test | grep used 020015f0 T aux__unused 02005d88 B aux__unused_data 020015cc T aux__used 02005d84 B aux__used_data $ gnatmake test -cargs -fdata-sections -ffunction-sections \ -largs -Wl,--gc-sections $ nm test | grep used 02005350 T aux__used 0201ffe0 B aux__used_data @end smallexample @noindent It can be observed that the procedure @code{Unused} and the object @code{Unused_Data} are removed by the linker when using the appropriate options. @c ******************************** @node Renaming Files Using gnatchop @chapter Renaming Files Using @code{gnatchop} @findex gnatchop @noindent This chapter discusses how to handle files with multiple units by using the @code{gnatchop} utility. This utility is also useful in renaming files to meet the standard GNAT default file naming conventions. @menu * Handling Files with Multiple Units:: * Operating gnatchop in Compilation Mode:: * Command Line for gnatchop:: * Switches for gnatchop:: * Examples of gnatchop Usage:: @end menu @node Handling Files with Multiple Units @section Handling Files with Multiple Units @noindent The basic compilation model of GNAT requires that a file submitted to the compiler have only one unit and there be a strict correspondence between the file name and the unit name. The @code{gnatchop} utility allows both of these rules to be relaxed, allowing GNAT to process files which contain multiple compilation units and files with arbitrary file names. @code{gnatchop} reads the specified file and generates one or more output files, containing one unit per file. The unit and the file name correspond, as required by GNAT. If you want to permanently restructure a set of ``foreign'' files so that they match the GNAT rules, and do the remaining development using the GNAT structure, you can simply use @command{gnatchop} once, generate the new set of files and work with them from that point on. Alternatively, if you want to keep your files in the ``foreign'' format, perhaps to maintain compatibility with some other Ada compilation system, you can set up a procedure where you use @command{gnatchop} each time you compile, regarding the source files that it writes as temporary files that you throw away. Note that if your file containing multiple units starts with a byte order mark (BOM) specifying UTF-8 encoding, then the files generated by gnatchop will each start with a copy of this BOM, meaning that they can be compiled automatically in UTF-8 mode without needing to specify an explicit encoding. @node Operating gnatchop in Compilation Mode @section Operating gnatchop in Compilation Mode @noindent The basic function of @code{gnatchop} is to take a file with multiple units and split it into separate files. The boundary between files is reasonably clear, except for the issue of comments and pragmas. In default mode, the rule is that any pragmas between units belong to the previous unit, except that configuration pragmas always belong to the following unit. Any comments belong to the following unit. These rules almost always result in the right choice of the split point without needing to mark it explicitly and most users will find this default to be what they want. In this default mode it is incorrect to submit a file containing only configuration pragmas, or one that ends in configuration pragmas, to @code{gnatchop}. However, using a special option to activate ``compilation mode'', @code{gnatchop} can perform another function, which is to provide exactly the semantics required by the RM for handling of configuration pragmas in a compilation. In the absence of configuration pragmas (at the main file level), this option has no effect, but it causes such configuration pragmas to be handled in a quite different manner. First, in compilation mode, if @code{gnatchop} is given a file that consists of only configuration pragmas, then this file is appended to the @file{gnat.adc} file in the current directory. This behavior provides the required behavior described in the RM for the actions to be taken on submitting such a file to the compiler, namely that these pragmas should apply to all subsequent compilations in the same compilation environment. Using GNAT, the current directory, possibly containing a @file{gnat.adc} file is the representation of a compilation environment. For more information on the @file{gnat.adc} file, see @ref{Handling of Configuration Pragmas}. Second, in compilation mode, if @code{gnatchop} is given a file that starts with configuration pragmas, and contains one or more units, then these configuration pragmas are prepended to each of the chopped files. This behavior provides the required behavior described in the RM for the actions to be taken on compiling such a file, namely that the pragmas apply to all units in the compilation, but not to subsequently compiled units. Finally, if configuration pragmas appear between units, they are appended to the previous unit. This results in the previous unit being illegal, since the compiler does not accept configuration pragmas that follow a unit. This provides the required RM behavior that forbids configuration pragmas other than those preceding the first compilation unit of a compilation. For most purposes, @code{gnatchop} will be used in default mode. The compilation mode described above is used only if you need exactly accurate behavior with respect to compilations, and you have files that contain multiple units and configuration pragmas. In this circumstance the use of @code{gnatchop} with the compilation mode switch provides the required behavior, and is for example the mode in which GNAT processes the ACVC tests. @node Command Line for gnatchop @section Command Line for @code{gnatchop} @noindent The @code{gnatchop} command has the form: @smallexample @c $ gnatchop switches @var{file name} @r{[}@var{file name} @dots{}@r{]} @c @ovar{directory} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatchop switches @var{file name} @r{[}@var{file name} @dots{}@r{]} @r{[}@var{directory}@r{]} @end smallexample @noindent The only required argument is the file name of the file to be chopped. There are no restrictions on the form of this file name. The file itself contains one or more Ada units, in normal GNAT format, concatenated together. As shown, more than one file may be presented to be chopped. When run in default mode, @code{gnatchop} generates one output file in the current directory for each unit in each of the files. @var{directory}, if specified, gives the name of the directory to which the output files will be written. If it is not specified, all files are written to the current directory. For example, given a file called @file{hellofiles} containing @smallexample @c ada @group @cartouche procedure hello; with Text_IO; use Text_IO; procedure hello is begin Put_Line ("Hello"); end hello; @end cartouche @end group @end smallexample @noindent the command @smallexample $ gnatchop ^hellofiles^HELLOFILES.^ @end smallexample @noindent generates two files in the current directory, one called @file{hello.ads} containing the single line that is the procedure spec, and the other called @file{hello.adb} containing the remaining text. The original file is not affected. The generated files can be compiled in the normal manner. @noindent When gnatchop is invoked on a file that is empty or that contains only empty lines and/or comments, gnatchop will not fail, but will not produce any new sources. For example, given a file called @file{toto.txt} containing @smallexample @c ada @group @cartouche -- Just a comment @end cartouche @end group @end smallexample @noindent the command @smallexample $ gnatchop ^toto.txt^TOT.TXT^ @end smallexample @noindent will not produce any new file and will result in the following warnings: @smallexample toto.txt:1:01: warning: empty file, contains no compilation units no compilation units found no source files written @end smallexample @node Switches for gnatchop @section Switches for @code{gnatchop} @noindent @command{gnatchop} recognizes the following switches: @table @option @c !sort! @item --version @cindex @option{--version} @command{gnatchop} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatchop} If @option{--version} was not used, display usage, then exit disregarding all other options. @item ^-c^/COMPILATION^ @cindex @option{^-c^/COMPILATION^} (@code{gnatchop}) Causes @code{gnatchop} to operate in compilation mode, in which configuration pragmas are handled according to strict RM rules. See previous section for a full description of this mode. @ifclear vms @item -gnat@var{xxx} This passes the given @option{-gnat@var{xxx}} switch to @code{gnat} which is used to parse the given file. Not all @var{xxx} options make sense, but for example, the use of @option{-gnati2} allows @code{gnatchop} to process a source file that uses Latin-2 coding for identifiers. @end ifclear @item ^-h^/HELP^ Causes @code{gnatchop} to generate a brief help summary to the standard output file showing usage information. @item ^-k@var{mm}^/FILE_NAME_MAX_LENGTH=@var{mm}^ @cindex @option{^-k^/FILE_NAME_MAX_LENGTH^} (@code{gnatchop}) Limit generated file names to the specified number @code{mm} of characters. This is useful if the resulting set of files is required to be interoperable with systems which limit the length of file names. @ifset vms If no value is given, or if no @code{/FILE_NAME_MAX_LENGTH} qualifier is given, a default of 39, suitable for OpenVMS Alpha Systems, is assumed @end ifset @ifclear vms No space is allowed between the @option{-k} and the numeric value. The numeric value may be omitted in which case a default of @option{-k8}, suitable for use with DOS-like file systems, is used. If no @option{-k} switch is present then there is no limit on the length of file names. @end ifclear @item ^-p^/PRESERVE^ @cindex @option{^-p^/PRESERVE^} (@code{gnatchop}) Causes the file ^modification^creation^ time stamp of the input file to be preserved and used for the time stamp of the output file(s). This may be useful for preserving coherency of time stamps in an environment where @code{gnatchop} is used as part of a standard build process. @item ^-q^/QUIET^ @cindex @option{^-q^/QUIET^} (@code{gnatchop}) Causes output of informational messages indicating the set of generated files to be suppressed. Warnings and error messages are unaffected. @item ^-r^/REFERENCE^ @cindex @option{^-r^/REFERENCE^} (@code{gnatchop}) @findex Source_Reference Generate @code{Source_Reference} pragmas. Use this switch if the output files are regarded as temporary and development is to be done in terms of the original unchopped file. This switch causes @code{Source_Reference} pragmas to be inserted into each of the generated files to refers back to the original file name and line number. The result is that all error messages refer back to the original unchopped file. In addition, the debugging information placed into the object file (when the @option{^-g^/DEBUG^} switch of @command{gcc} or @command{gnatmake} is specified) also refers back to this original file so that tools like profilers and debuggers will give information in terms of the original unchopped file. If the original file to be chopped itself contains a @code{Source_Reference} pragma referencing a third file, then gnatchop respects this pragma, and the generated @code{Source_Reference} pragmas in the chopped file refer to the original file, with appropriate line numbers. This is particularly useful when @code{gnatchop} is used in conjunction with @code{gnatprep} to compile files that contain preprocessing statements and multiple units. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@code{gnatchop}) Causes @code{gnatchop} to operate in verbose mode. The version number and copyright notice are output, as well as exact copies of the gnat1 commands spawned to obtain the chop control information. @item ^-w^/OVERWRITE^ @cindex @option{^-w^/OVERWRITE^} (@code{gnatchop}) Overwrite existing file names. Normally @code{gnatchop} regards it as a fatal error if there is already a file with the same name as a file it would otherwise output, in other words if the files to be chopped contain duplicated units. This switch bypasses this check, and causes all but the last instance of such duplicated units to be skipped. @ifclear vms @item --GCC=@var{xxxx} @cindex @option{--GCC=} (@code{gnatchop}) Specify the path of the GNAT parser to be used. When this switch is used, no attempt is made to add the prefix to the GNAT parser executable. @end ifclear @end table @node Examples of gnatchop Usage @section Examples of @code{gnatchop} Usage @table @code @ifset vms @item gnatchop /OVERWRITE HELLO_S.ADA [PRERELEASE.FILES] @end ifset @ifclear vms @item gnatchop -w hello_s.ada prerelease/files @end ifclear Chops the source file @file{hello_s.ada}. The output files will be placed in the directory @file{^prerelease/files^[PRERELEASE.FILES]^}, overwriting any files with matching names in that directory (no files in the current directory are modified). @item gnatchop ^archive^ARCHIVE.^ Chops the source file @file{^archive^ARCHIVE.^} into the current directory. One useful application of @code{gnatchop} is in sending sets of sources around, for example in email messages. The required sources are simply concatenated (for example, using a ^Unix @code{cat}^VMS @code{APPEND/NEW}^ command), and then @command{gnatchop} is used at the other end to reconstitute the original file names. @item gnatchop file1 file2 file3 direc Chops all units in files @file{file1}, @file{file2}, @file{file3}, placing the resulting files in the directory @file{direc}. Note that if any units occur more than once anywhere within this set of files, an error message is generated, and no files are written. To override this check, use the @option{^-w^/OVERWRITE^} switch, in which case the last occurrence in the last file will be the one that is output, and earlier duplicate occurrences for a given unit will be skipped. @end table @node Configuration Pragmas @chapter Configuration Pragmas @cindex Configuration pragmas @cindex Pragmas, configuration @noindent Configuration pragmas include those pragmas described as such in the Ada Reference Manual, as well as implementation-dependent pragmas that are configuration pragmas. @xref{Implementation Defined Pragmas,,, gnat_rm, GNAT Reference Manual}, for details on these additional GNAT-specific configuration pragmas. Most notably, the pragma @code{Source_File_Name}, which allows specifying non-default names for source files, is a configuration pragma. The following is a complete list of configuration pragmas recognized by GNAT: @smallexample Ada_83 Ada_95 Ada_05 Ada_2005 Ada_12 Ada_2012 Assertion_Policy Assume_No_Invalid_Values C_Pass_By_Copy Check_Name Check_Policy Compile_Time_Error Compile_Time_Warning Compiler_Unit Component_Alignment Convention_Identifier Debug_Policy Detect_Blocking Discard_Names Elaboration_Checks Eliminate Extend_System Extensions_Allowed External_Name_Casing Fast_Math Favor_Top_Level Float_Representation Implicit_Packing Initialize_Scalars Interrupt_State License Locking_Policy Long_Float No_Run_Time No_Strict_Aliasing Normalize_Scalars Optimize_Alignment Persistent_BSS Polling Priority_Specific_Dispatching Profile Profile_Warnings Propagate_Exceptions Queuing_Policy Ravenscar Restricted_Run_Time Restrictions Restrictions_Warnings Reviewable Short_Circuit_And_Or Source_File_Name Source_File_Name_Project Style_Checks Suppress Suppress_Exception_Locations Task_Dispatching_Policy Universal_Data Unsuppress Use_VADS_Size Validity_Checks Warnings Wide_Character_Encoding @end smallexample @menu * Handling of Configuration Pragmas:: * The Configuration Pragmas Files:: @end menu @node Handling of Configuration Pragmas @section Handling of Configuration Pragmas Configuration pragmas may either appear at the start of a compilation unit, in which case they apply only to that unit, or they may apply to all compilations performed in a given compilation environment. GNAT also provides the @code{gnatchop} utility to provide an automatic way to handle configuration pragmas following the semantics for compilations (that is, files with multiple units), described in the RM. See @ref{Operating gnatchop in Compilation Mode} for details. However, for most purposes, it will be more convenient to edit the @file{gnat.adc} file that contains configuration pragmas directly, as described in the following section. @node The Configuration Pragmas Files @section The Configuration Pragmas Files @cindex @file{gnat.adc} @noindent In GNAT a compilation environment is defined by the current directory at the time that a compile command is given. This current directory is searched for a file whose name is @file{gnat.adc}. If this file is present, it is expected to contain one or more configuration pragmas that will be applied to the current compilation. However, if the switch @option{-gnatA} is used, @file{gnat.adc} is not considered. Configuration pragmas may be entered into the @file{gnat.adc} file either by running @code{gnatchop} on a source file that consists only of configuration pragmas, or more conveniently by direct editing of the @file{gnat.adc} file, which is a standard format source file. In addition to @file{gnat.adc}, additional files containing configuration pragmas may be applied to the current compilation using the switch @option{-gnatec}@var{path}. @var{path} must designate an existing file that contains only configuration pragmas. These configuration pragmas are in addition to those found in @file{gnat.adc} (provided @file{gnat.adc} is present and switch @option{-gnatA} is not used). It is allowed to specify several switches @option{-gnatec}, all of which will be taken into account. If you are using project file, a separate mechanism is provided using project attributes, see @ref{Specifying Configuration Pragmas} for more details. @ifset vms Of special interest to GNAT OpenVMS Alpha is the following configuration pragma: @smallexample @c ada @cartouche pragma Extend_System (Aux_DEC); @end cartouche @end smallexample @noindent In the presence of this pragma, GNAT adds to the definition of the predefined package SYSTEM all the additional types and subprograms that are defined in HP Ada. See @ref{Compatibility with HP Ada} for details. @end ifset @node Handling Arbitrary File Naming Conventions Using gnatname @chapter Handling Arbitrary File Naming Conventions Using @code{gnatname} @cindex Arbitrary File Naming Conventions @menu * Arbitrary File Naming Conventions:: * Running gnatname:: * Switches for gnatname:: * Examples of gnatname Usage:: @end menu @node Arbitrary File Naming Conventions @section Arbitrary File Naming Conventions @noindent The GNAT compiler must be able to know the source file name of a compilation unit. When using the standard GNAT default file naming conventions (@code{.ads} for specs, @code{.adb} for bodies), the GNAT compiler does not need additional information. @noindent When the source file names do not follow the standard GNAT default file naming conventions, the GNAT compiler must be given additional information through a configuration pragmas file (@pxref{Configuration Pragmas}) or a project file. When the non-standard file naming conventions are well-defined, a small number of pragmas @code{Source_File_Name} specifying a naming pattern (@pxref{Alternative File Naming Schemes}) may be sufficient. However, if the file naming conventions are irregular or arbitrary, a number of pragma @code{Source_File_Name} for individual compilation units must be defined. To help maintain the correspondence between compilation unit names and source file names within the compiler, GNAT provides a tool @code{gnatname} to generate the required pragmas for a set of files. @node Running gnatname @section Running @code{gnatname} @noindent The usual form of the @code{gnatname} command is @smallexample @c $ gnatname @ovar{switches} @var{naming_pattern} @ovar{naming_patterns} @c @r{[}--and @ovar{switches} @var{naming_pattern} @ovar{naming_patterns}@r{]} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatname @r{[}@var{switches}@r{]} @var{naming_pattern} @r{[}@var{naming_patterns}@r{]} @r{[}--and @r{[}@var{switches}@r{]} @var{naming_pattern} @r{[}@var{naming_patterns}@r{]}@r{]} @end smallexample @noindent All of the arguments are optional. If invoked without any argument, @code{gnatname} will display its usage. @noindent When used with at least one naming pattern, @code{gnatname} will attempt to find all the compilation units in files that follow at least one of the naming patterns. To find these compilation units, @code{gnatname} will use the GNAT compiler in syntax-check-only mode on all regular files. @noindent One or several Naming Patterns may be given as arguments to @code{gnatname}. Each Naming Pattern is enclosed between double quotes (or single quotes on Windows). A Naming Pattern is a regular expression similar to the wildcard patterns used in file names by the Unix shells or the DOS prompt. @noindent @code{gnatname} may be called with several sections of directories/patterns. Sections are separated by switch @code{--and}. In each section, there must be at least one pattern. If no directory is specified in a section, the current directory (or the project directory is @code{-P} is used) is implied. The options other that the directory switches and the patterns apply globally even if they are in different sections. @noindent Examples of Naming Patterns are @smallexample "*.[12].ada" "*.ad[sb]*" "body_*" "spec_*" @end smallexample @noindent For a more complete description of the syntax of Naming Patterns, see the second kind of regular expressions described in @file{g-regexp.ads} (the ``Glob'' regular expressions). @noindent When invoked with no switch @code{-P}, @code{gnatname} will create a configuration pragmas file @file{gnat.adc} in the current working directory, with pragmas @code{Source_File_Name} for each file that contains a valid Ada unit. @node Switches for gnatname @section Switches for @code{gnatname} @noindent Switches for @code{gnatname} must precede any specified Naming Pattern. @noindent You may specify any of the following switches to @code{gnatname}: @table @option @c !sort! @item --version @cindex @option{--version} @command{gnatname} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatname} If @option{--version} was not used, display usage, then exit disregarding all other options. @item --and Start another section of directories/patterns. @item ^-c^/CONFIG_FILE=^@file{file} @cindex @option{^-c^/CONFIG_FILE^} (@code{gnatname}) Create a configuration pragmas file @file{file} (instead of the default @file{gnat.adc}). @ifclear vms There may be zero, one or more space between @option{-c} and @file{file}. @end ifclear @file{file} may include directory information. @file{file} must be writable. There may be only one switch @option{^-c^/CONFIG_FILE^}. When a switch @option{^-c^/CONFIG_FILE^} is specified, no switch @option{^-P^/PROJECT_FILE^} may be specified (see below). @item ^-d^/SOURCE_DIRS=^@file{dir} @cindex @option{^-d^/SOURCE_DIRS^} (@code{gnatname}) Look for source files in directory @file{dir}. There may be zero, one or more spaces between @option{^-d^/SOURCE_DIRS=^} and @file{dir}. When a switch @option{^-d^/SOURCE_DIRS^} is specified, the current working directory will not be searched for source files, unless it is explicitly specified with a @option{^-d^/SOURCE_DIRS^} or @option{^-D^/DIR_FILES^} switch. Several switches @option{^-d^/SOURCE_DIRS^} may be specified. If @file{dir} is a relative path, it is relative to the directory of the configuration pragmas file specified with switch @option{^-c^/CONFIG_FILE^}, or to the directory of the project file specified with switch @option{^-P^/PROJECT_FILE^} or, if neither switch @option{^-c^/CONFIG_FILE^} nor switch @option{^-P^/PROJECT_FILE^} are specified, it is relative to the current working directory. The directory specified with switch @option{^-d^/SOURCE_DIRS^} must exist and be readable. @item ^-D^/DIRS_FILE=^@file{file} @cindex @option{^-D^/DIRS_FILE^} (@code{gnatname}) Look for source files in all directories listed in text file @file{file}. There may be zero, one or more spaces between @option{^-D^/DIRS_FILE=^} and @file{file}. @file{file} must be an existing, readable text file. Each nonempty line in @file{file} must be a directory. Specifying switch @option{^-D^/DIRS_FILE^} is equivalent to specifying as many switches @option{^-d^/SOURCE_DIRS^} as there are nonempty lines in @file{file}. @item ^-f^/FOREIGN_PATTERN=^@file{pattern} @cindex @option{^-f^/FOREIGN_PATTERN^} (@code{gnatname}) Foreign patterns. Using this switch, it is possible to add sources of languages other than Ada to the list of sources of a project file. It is only useful if a ^-P^/PROJECT_FILE^ switch is used. For example, @smallexample gnatname ^-Pprj -f"*.c"^/PROJECT_FILE=PRJ /FOREIGN_PATTERN=*.C^ "*.ada" @end smallexample @noindent will look for Ada units in all files with the @file{.ada} extension, and will add to the list of file for project @file{prj.gpr} the C files with extension @file{.^c^C^}. @item ^-h^/HELP^ @cindex @option{^-h^/HELP^} (@code{gnatname}) Output usage (help) information. The output is written to @file{stdout}. @item ^-P^/PROJECT_FILE=^@file{proj} @cindex @option{^-P^/PROJECT_FILE^} (@code{gnatname}) Create or update project file @file{proj}. There may be zero, one or more space between @option{-P} and @file{proj}. @file{proj} may include directory information. @file{proj} must be writable. There may be only one switch @option{^-P^/PROJECT_FILE^}. When a switch @option{^-P^/PROJECT_FILE^} is specified, no switch @option{^-c^/CONFIG_FILE^} may be specified. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@code{gnatname}) Verbose mode. Output detailed explanation of behavior to @file{stdout}. This includes name of the file written, the name of the directories to search and, for each file in those directories whose name matches at least one of the Naming Patterns, an indication of whether the file contains a unit, and if so the name of the unit. @item ^-v -v^/VERBOSE /VERBOSE^ @cindex @option{^-v -v^/VERBOSE /VERBOSE^} (@code{gnatname}) Very Verbose mode. In addition to the output produced in verbose mode, for each file in the searched directories whose name matches none of the Naming Patterns, an indication is given that there is no match. @item ^-x^/EXCLUDED_PATTERN=^@file{pattern} @cindex @option{^-x^/EXCLUDED_PATTERN^} (@code{gnatname}) Excluded patterns. Using this switch, it is possible to exclude some files that would match the name patterns. For example, @smallexample gnatname ^-x "*_nt.ada"^/EXCLUDED_PATTERN=*_nt.ada^ "*.ada" @end smallexample @noindent will look for Ada units in all files with the @file{.ada} extension, except those whose names end with @file{_nt.ada}. @end table @node Examples of gnatname Usage @section Examples of @code{gnatname} Usage @ifset vms @smallexample $ gnatname /CONFIG_FILE=[HOME.ME]NAMES.ADC /SOURCE_DIRS=SOURCES "[a-z]*.ada*" @end smallexample @end ifset @ifclear vms @smallexample $ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*" @end smallexample @end ifclear @noindent In this example, the directory @file{^/home/me^[HOME.ME]^} must already exist and be writable. In addition, the directory @file{^/home/me/sources^[HOME.ME.SOURCES]^} (specified by @option{^-d sources^/SOURCE_DIRS=SOURCES^}) must exist and be readable. @ifclear vms Note the optional spaces after @option{-c} and @option{-d}. @end ifclear @smallexample @ifclear vms $ gnatname -P/home/me/proj -x "*_nt_body.ada" -dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*" @end ifclear @ifset vms $ gnatname /PROJECT_FILE=[HOME.ME]PROJ /EXCLUDED_PATTERN=*_nt_body.ada /SOURCE_DIRS=(SOURCES,[SOURCES.PLUS]) /DIRS_FILE=COMMON_DIRS.TXT "body_*" "spec_*" @end ifset @end smallexample Note that several switches @option{^-d^/SOURCE_DIRS^} may be used, even in conjunction with one or several switches @option{^-D^/DIRS_FILE^}. Several Naming Patterns and one excluded pattern are used in this example. @c ***************************************** @c * G N A T P r o j e c t M a n a g e r * @c ***************************************** @c ------ macros for projects.texi @c These macros are needed when building the gprbuild documentation, but @c should have no effect in the gnat user's guide @macro CODESAMPLE{TXT} @smallexample @group \TXT\ @end group @end smallexample @end macro @macro PROJECTFILE{TXT} @CODESAMPLE{\TXT\} @end macro @c simulates a newline when in a @CODESAMPLE @macro NL{} @end macro @macro TIP{TXT} @quotation @noindent \TXT\ @end quotation @end macro @macro TIPHTML{TXT} \TXT\ @end macro @macro IMPORTANT{TXT} @quotation @noindent \TXT\ @end quotation @end macro @macro NOTE{TXT} @quotation @noindent \TXT\ @end quotation @end macro @include projects.texi @c ***************************************** @c * Cross-referencing tools @c ***************************************** @node The Cross-Referencing Tools gnatxref and gnatfind @chapter The Cross-Referencing Tools @code{gnatxref} and @code{gnatfind} @findex gnatxref @findex gnatfind @noindent The compiler generates cross-referencing information (unless you set the @samp{-gnatx} switch), which are saved in the @file{.ali} files. This information indicates where in the source each entity is declared and referenced. Note that entities in package Standard are not included, but entities in all other predefined units are included in the output. Before using any of these two tools, you need to compile successfully your application, so that GNAT gets a chance to generate the cross-referencing information. The two tools @code{gnatxref} and @code{gnatfind} take advantage of this information to provide the user with the capability to easily locate the declaration and references to an entity. These tools are quite similar, the difference being that @code{gnatfind} is intended for locating definitions and/or references to a specified entity or entities, whereas @code{gnatxref} is oriented to generating a full report of all cross-references. To use these tools, you must not compile your application using the @option{-gnatx} switch on the @command{gnatmake} command line (@pxref{The GNAT Make Program gnatmake}). Otherwise, cross-referencing information will not be generated. Note: to invoke @code{gnatxref} or @code{gnatfind} with a project file, use the @code{gnat} driver (see @ref{The GNAT Driver and Project Files}). @menu * Switches for gnatxref:: * Switches for gnatfind:: * Project Files for gnatxref and gnatfind:: * Regular Expressions in gnatfind and gnatxref:: * Examples of gnatxref Usage:: * Examples of gnatfind Usage:: @end menu @node Switches for gnatxref @section @code{gnatxref} Switches @noindent The command invocation for @code{gnatxref} is: @smallexample @c $ gnatxref @ovar{switches} @var{sourcefile1} @r{[}@var{sourcefile2} @dots{}@r{]} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatxref @r{[}@var{switches}@r{]} @var{sourcefile1} @r{[}@var{sourcefile2} @dots{}@r{]} @end smallexample @noindent where @table @var @item sourcefile1 @itemx sourcefile2 identifies the source files for which a report is to be generated. The ``with''ed units will be processed too. You must provide at least one file. These file names are considered to be regular expressions, so for instance specifying @file{source*.adb} is the same as giving every file in the current directory whose name starts with @file{source} and whose extension is @file{adb}. You shouldn't specify any directory name, just base names. @command{gnatxref} and @command{gnatfind} will be able to locate these files by themselves using the source path. If you specify directories, no result is produced. @end table @noindent The switches can be: @table @option @c !sort! @item --version @cindex @option{--version} @command{gnatxref} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatxref} If @option{--version} was not used, display usage, then exit disregarding all other options. @item ^-a^/ALL_FILES^ @cindex @option{^-a^/ALL_FILES^} (@command{gnatxref}) If this switch is present, @code{gnatfind} and @code{gnatxref} will parse the read-only files found in the library search path. Otherwise, these files will be ignored. This option can be used to protect Gnat sources or your own libraries from being parsed, thus making @code{gnatfind} and @code{gnatxref} much faster, and their output much smaller. Read-only here refers to access or permissions status in the file system for the current user. @item -aIDIR @cindex @option{-aIDIR} (@command{gnatxref}) When looking for source files also look in directory DIR. The order in which source file search is undertaken is the same as for @command{gnatmake}. @item -aODIR @cindex @option{-aODIR} (@command{gnatxref}) When searching for library and object files, look in directory DIR. The order in which library files are searched is the same as for @command{gnatmake}. @item -nostdinc @cindex @option{-nostdinc} (@command{gnatxref}) Do not look for sources in the system default directory. @item -nostdlib @cindex @option{-nostdlib} (@command{gnatxref}) Do not look for library files in the system default directory. @item --ext=@var{extension} @cindex @option{--ext} (@command{gnatxref}) Specify an alternate ali file extension. The default is @code{ali} and other extensions (e.g. @code{sli} for SPARK library files) may be specified via this switch. Note that if this switch overrides the default, which means that only the new extension will be considered. @item --RTS=@var{rts-path} @cindex @option{--RTS} (@command{gnatxref}) Specifies the default location of the runtime library. Same meaning as the equivalent @command{gnatmake} flag (@pxref{Switches for gnatmake}). @item ^-d^/DERIVED_TYPES^ @cindex @option{^-d^/DERIVED_TYPES^} (@command{gnatxref}) If this switch is set @code{gnatxref} will output the parent type reference for each matching derived types. @item ^-f^/FULL_PATHNAME^ @cindex @option{^-f^/FULL_PATHNAME^} (@command{gnatxref}) If this switch is set, the output file names will be preceded by their directory (if the file was found in the search path). If this switch is not set, the directory will not be printed. @item ^-g^/IGNORE_LOCALS^ @cindex @option{^-g^/IGNORE_LOCALS^} (@command{gnatxref}) If this switch is set, information is output only for library-level entities, ignoring local entities. The use of this switch may accelerate @code{gnatfind} and @code{gnatxref}. @item -IDIR @cindex @option{-IDIR} (@command{gnatxref}) Equivalent to @samp{-aODIR -aIDIR}. @item -pFILE @cindex @option{-pFILE} (@command{gnatxref}) Specify a project file to use @xref{GNAT Project Manager}. If you need to use the @file{.gpr} project files, you should use gnatxref through the GNAT driver (@command{gnat xref -Pproject}). By default, @code{gnatxref} and @code{gnatfind} will try to locate a project file in the current directory. If a project file is either specified or found by the tools, then the content of the source directory and object directory lines are added as if they had been specified respectively by @samp{^-aI^/SOURCE_SEARCH^} and @samp{^-aO^OBJECT_SEARCH^}. @item ^-u^/UNUSED^ Output only unused symbols. This may be really useful if you give your main compilation unit on the command line, as @code{gnatxref} will then display every unused entity and 'with'ed package. @ifclear vms @item -v Instead of producing the default output, @code{gnatxref} will generate a @file{tags} file that can be used by vi. For examples how to use this feature, see @ref{Examples of gnatxref Usage}. The tags file is output to the standard output, thus you will have to redirect it to a file. @end ifclear @end table @noindent All these switches may be in any order on the command line, and may even appear after the file names. They need not be separated by spaces, thus you can say @samp{gnatxref ^-ag^/ALL_FILES/IGNORE_LOCALS^} instead of @samp{gnatxref ^-a -g^/ALL_FILES /IGNORE_LOCALS^}. @node Switches for gnatfind @section @code{gnatfind} Switches @noindent The command line for @code{gnatfind} is: @smallexample @c $ gnatfind @ovar{switches} @var{pattern}@r{[}:@var{sourcefile}@r{[}:@var{line}@r{[}:@var{column}@r{]]]} @c @r{[}@var{file1} @var{file2} @dots{}] @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatfind @r{[}@var{switches}@r{]} @var{pattern}@r{[}:@var{sourcefile}@r{[}:@var{line}@r{[}:@var{column}@r{]]]} @r{[}@var{file1} @var{file2} @dots{}@r{]} @end smallexample @noindent where @table @var @item pattern An entity will be output only if it matches the regular expression found in @var{pattern}, see @ref{Regular Expressions in gnatfind and gnatxref}. Omitting the pattern is equivalent to specifying @samp{*}, which will match any entity. Note that if you do not provide a pattern, you have to provide both a sourcefile and a line. Entity names are given in Latin-1, with uppercase/lowercase equivalence for matching purposes. At the current time there is no support for 8-bit codes other than Latin-1, or for wide characters in identifiers. @item sourcefile @code{gnatfind} will look for references, bodies or declarations of symbols referenced in @file{@var{sourcefile}}, at line @var{line} and column @var{column}. See @ref{Examples of gnatfind Usage} for syntax examples. @item line is a decimal integer identifying the line number containing the reference to the entity (or entities) to be located. @item column is a decimal integer identifying the exact location on the line of the first character of the identifier for the entity reference. Columns are numbered from 1. @item file1 file2 @dots{} The search will be restricted to these source files. If none are given, then the search will be done for every library file in the search path. These file must appear only after the pattern or sourcefile. These file names are considered to be regular expressions, so for instance specifying @file{source*.adb} is the same as giving every file in the current directory whose name starts with @file{source} and whose extension is @file{adb}. The location of the spec of the entity will always be displayed, even if it isn't in one of @file{@var{file1}}, @file{@var{file2}},@enddots{} The occurrences of the entity in the separate units of the ones given on the command line will also be displayed. Note that if you specify at least one file in this part, @code{gnatfind} may sometimes not be able to find the body of the subprograms. @end table @noindent At least one of 'sourcefile' or 'pattern' has to be present on the command line. The following switches are available: @table @option @c !sort! @cindex @option{--version} @command{gnatfind} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatfind} If @option{--version} was not used, display usage, then exit disregarding all other options. @item ^-a^/ALL_FILES^ @cindex @option{^-a^/ALL_FILES^} (@command{gnatfind}) If this switch is present, @code{gnatfind} and @code{gnatxref} will parse the read-only files found in the library search path. Otherwise, these files will be ignored. This option can be used to protect Gnat sources or your own libraries from being parsed, thus making @code{gnatfind} and @code{gnatxref} much faster, and their output much smaller. Read-only here refers to access or permission status in the file system for the current user. @item -aIDIR @cindex @option{-aIDIR} (@command{gnatfind}) When looking for source files also look in directory DIR. The order in which source file search is undertaken is the same as for @command{gnatmake}. @item -aODIR @cindex @option{-aODIR} (@command{gnatfind}) When searching for library and object files, look in directory DIR. The order in which library files are searched is the same as for @command{gnatmake}. @item -nostdinc @cindex @option{-nostdinc} (@command{gnatfind}) Do not look for sources in the system default directory. @item -nostdlib @cindex @option{-nostdlib} (@command{gnatfind}) Do not look for library files in the system default directory. @item --ext=@var{extension} @cindex @option{--ext} (@command{gnatfind}) Specify an alternate ali file extension. The default is @code{ali} and other extensions (e.g. @code{sli} for SPARK library files) may be specified via this switch. Note that if this switch overrides the default, which means that only the new extension will be considered. @item --RTS=@var{rts-path} @cindex @option{--RTS} (@command{gnatfind}) Specifies the default location of the runtime library. Same meaning as the equivalent @command{gnatmake} flag (@pxref{Switches for gnatmake}). @item ^-d^/DERIVED_TYPE_INFORMATION^ @cindex @option{^-d^/DERIVED_TYPE_INFORMATION^} (@code{gnatfind}) If this switch is set, then @code{gnatfind} will output the parent type reference for each matching derived types. @item ^-e^/EXPRESSIONS^ @cindex @option{^-e^/EXPRESSIONS^} (@command{gnatfind}) By default, @code{gnatfind} accept the simple regular expression set for @samp{pattern}. If this switch is set, then the pattern will be considered as full Unix-style regular expression. @item ^-f^/FULL_PATHNAME^ @cindex @option{^-f^/FULL_PATHNAME^} (@command{gnatfind}) If this switch is set, the output file names will be preceded by their directory (if the file was found in the search path). If this switch is not set, the directory will not be printed. @item ^-g^/IGNORE_LOCALS^ @cindex @option{^-g^/IGNORE_LOCALS^} (@command{gnatfind}) If this switch is set, information is output only for library-level entities, ignoring local entities. The use of this switch may accelerate @code{gnatfind} and @code{gnatxref}. @item -IDIR @cindex @option{-IDIR} (@command{gnatfind}) Equivalent to @samp{-aODIR -aIDIR}. @item -pFILE @cindex @option{-pFILE} (@command{gnatfind}) Specify a project file (@pxref{GNAT Project Manager}) to use. By default, @code{gnatxref} and @code{gnatfind} will try to locate a project file in the current directory. If a project file is either specified or found by the tools, then the content of the source directory and object directory lines are added as if they had been specified respectively by @samp{^-aI^/SOURCE_SEARCH^} and @samp{^-aO^/OBJECT_SEARCH^}. @item ^-r^/REFERENCES^ @cindex @option{^-r^/REFERENCES^} (@command{gnatfind}) By default, @code{gnatfind} will output only the information about the declaration, body or type completion of the entities. If this switch is set, the @code{gnatfind} will locate every reference to the entities in the files specified on the command line (or in every file in the search path if no file is given on the command line). @item ^-s^/PRINT_LINES^ @cindex @option{^-s^/PRINT_LINES^} (@command{gnatfind}) If this switch is set, then @code{gnatfind} will output the content of the Ada source file lines were the entity was found. @item ^-t^/TYPE_HIERARCHY^ @cindex @option{^-t^/TYPE_HIERARCHY^} (@command{gnatfind}) If this switch is set, then @code{gnatfind} will output the type hierarchy for the specified type. It act like -d option but recursively from parent type to parent type. When this switch is set it is not possible to specify more than one file. @end table @noindent All these switches may be in any order on the command line, and may even appear after the file names. They need not be separated by spaces, thus you can say @samp{gnatxref ^-ag^/ALL_FILES/IGNORE_LOCALS^} instead of @samp{gnatxref ^-a -g^/ALL_FILES /IGNORE_LOCALS^}. As stated previously, gnatfind will search in every directory in the search path. You can force it to look only in the current directory if you specify @code{*} at the end of the command line. @node Project Files for gnatxref and gnatfind @section Project Files for @command{gnatxref} and @command{gnatfind} @noindent Project files allow a programmer to specify how to compile its application, where to find sources, etc. These files are used @ifclear vms primarily by GPS, but they can also be used @end ifclear by the two tools @code{gnatxref} and @code{gnatfind}. A project file name must end with @file{.gpr}. If a single one is present in the current directory, then @code{gnatxref} and @code{gnatfind} will extract the information from it. If multiple project files are found, none of them is read, and you have to use the @samp{-p} switch to specify the one you want to use. The following lines can be included, even though most of them have default values which can be used in most cases. The lines can be entered in any order in the file. Except for @file{src_dir} and @file{obj_dir}, you can only have one instance of each line. If you have multiple instances, only the last one is taken into account. @table @code @item src_dir=DIR [default: @code{"^./^[]^"}] specifies a directory where to look for source files. Multiple @code{src_dir} lines can be specified and they will be searched in the order they are specified. @item obj_dir=DIR [default: @code{"^./^[]^"}] specifies a directory where to look for object and library files. Multiple @code{obj_dir} lines can be specified, and they will be searched in the order they are specified @item comp_opt=SWITCHES [default: @code{""}] creates a variable which can be referred to subsequently by using the @code{$@{comp_opt@}} notation. This is intended to store the default switches given to @command{gnatmake} and @command{gcc}. @item bind_opt=SWITCHES [default: @code{""}] creates a variable which can be referred to subsequently by using the @samp{$@{bind_opt@}} notation. This is intended to store the default switches given to @command{gnatbind}. @item link_opt=SWITCHES [default: @code{""}] creates a variable which can be referred to subsequently by using the @samp{$@{link_opt@}} notation. This is intended to store the default switches given to @command{gnatlink}. @item main=EXECUTABLE [default: @code{""}] specifies the name of the executable for the application. This variable can be referred to in the following lines by using the @samp{$@{main@}} notation. @ifset vms @item comp_cmd=COMMAND [default: @code{"GNAT COMPILE /SEARCH=$@{src_dir@} /DEBUG /TRY_SEMANTICS"}] @end ifset @ifclear vms @item comp_cmd=COMMAND [default: @code{"gcc -c -I$@{src_dir@} -g -gnatq"}] @end ifclear specifies the command used to compile a single file in the application. @ifset vms @item make_cmd=COMMAND [default: @code{"GNAT MAKE $@{main@} /SOURCE_SEARCH=$@{src_dir@} /OBJECT_SEARCH=$@{obj_dir@} /DEBUG /TRY_SEMANTICS /COMPILER_QUALIFIERS $@{comp_opt@} /BINDER_QUALIFIERS $@{bind_opt@} /LINKER_QUALIFIERS $@{link_opt@}"}] @end ifset @ifclear vms @item make_cmd=COMMAND [default: @code{"gnatmake $@{main@} -aI$@{src_dir@} -aO$@{obj_dir@} -g -gnatq -cargs $@{comp_opt@} -bargs $@{bind_opt@} -largs $@{link_opt@}"}] @end ifclear specifies the command used to recompile the whole application. @item run_cmd=COMMAND [default: @code{"$@{main@}"}] specifies the command used to run the application. @item debug_cmd=COMMAND [default: @code{"gdb $@{main@}"}] specifies the command used to debug the application @end table @noindent @command{gnatxref} and @command{gnatfind} only take into account the @code{src_dir} and @code{obj_dir} lines, and ignore the others. @node Regular Expressions in gnatfind and gnatxref @section Regular Expressions in @code{gnatfind} and @code{gnatxref} @noindent As specified in the section about @command{gnatfind}, the pattern can be a regular expression. Actually, there are to set of regular expressions which are recognized by the program: @table @code @item globbing patterns These are the most usual regular expression. They are the same that you generally used in a Unix shell command line, or in a DOS session. Here is a more formal grammar: @smallexample @group @iftex @leftskip=.5cm @end iftex regexp ::= term term ::= elmt -- matches elmt term ::= elmt elmt -- concatenation (elmt then elmt) term ::= * -- any string of 0 or more characters term ::= ? -- matches any character term ::= [char @{char@}] -- matches any character listed term ::= [char - char] -- matches any character in range @end group @end smallexample @item full regular expression The second set of regular expressions is much more powerful. This is the type of regular expressions recognized by utilities such a @file{grep}. The following is the form of a regular expression, expressed in Ada reference manual style BNF is as follows @smallexample @iftex @leftskip=.5cm @end iftex @group regexp ::= term @{| term@} -- alternation (term or term @dots{}) term ::= item @{item@} -- concatenation (item then item) item ::= elmt -- match elmt item ::= elmt * -- zero or more elmt's item ::= elmt + -- one or more elmt's item ::= elmt ? -- matches elmt or nothing @end group @group elmt ::= nschar -- matches given character elmt ::= [nschar @{nschar@}] -- matches any character listed elmt ::= [^^^ nschar @{nschar@}] -- matches any character not listed elmt ::= [char - char] -- matches chars in given range elmt ::= \ char -- matches given character elmt ::= . -- matches any single character elmt ::= ( regexp ) -- parens used for grouping char ::= any character, including special characters nschar ::= any character except ()[].*+?^^^ @end group @end smallexample Following are a few examples: @table @samp @item abcde|fghi will match any of the two strings @samp{abcde} and @samp{fghi}, @item abc*d will match any string like @samp{abd}, @samp{abcd}, @samp{abccd}, @samp{abcccd}, and so on, @item [a-z]+ will match any string which has only lowercase characters in it (and at least one character. @end table @end table @node Examples of gnatxref Usage @section Examples of @code{gnatxref} Usage @subsection General Usage @noindent For the following examples, we will consider the following units: @smallexample @c ada @group @cartouche main.ads: 1: with Bar; 2: package Main is 3: procedure Foo (B : in Integer); 4: C : Integer; 5: private 6: D : Integer; 7: end Main; main.adb: 1: package body Main is 2: procedure Foo (B : in Integer) is 3: begin 4: C := B; 5: D := B; 6: Bar.Print (B); 7: Bar.Print (C); 8: end Foo; 9: end Main; bar.ads: 1: package Bar is 2: procedure Print (B : Integer); 3: end bar; @end cartouche @end group @end smallexample @table @code @noindent The first thing to do is to recompile your application (for instance, in that case just by doing a @samp{gnatmake main}, so that GNAT generates the cross-referencing information. You can then issue any of the following commands: @item gnatxref main.adb @code{gnatxref} generates cross-reference information for main.adb and every unit 'with'ed by main.adb. The output would be: @smallexample @iftex @leftskip=0cm @end iftex B Type: Integer Decl: bar.ads 2:22 B Type: Integer Decl: main.ads 3:20 Body: main.adb 2:20 Ref: main.adb 4:13 5:13 6:19 Bar Type: Unit Decl: bar.ads 1:9 Ref: main.adb 6:8 7:8 main.ads 1:6 C Type: Integer Decl: main.ads 4:5 Modi: main.adb 4:8 Ref: main.adb 7:19 D Type: Integer Decl: main.ads 6:5 Modi: main.adb 5:8 Foo Type: Unit Decl: main.ads 3:15 Body: main.adb 2:15 Main Type: Unit Decl: main.ads 2:9 Body: main.adb 1:14 Print Type: Unit Decl: bar.ads 2:15 Ref: main.adb 6:12 7:12 @end smallexample @noindent that is the entity @code{Main} is declared in main.ads, line 2, column 9, its body is in main.adb, line 1, column 14 and is not referenced any where. The entity @code{Print} is declared in bar.ads, line 2, column 15 and it it referenced in main.adb, line 6 column 12 and line 7 column 12. @item gnatxref package1.adb package2.ads @code{gnatxref} will generates cross-reference information for package1.adb, package2.ads and any other package 'with'ed by any of these. @end table @ifclear vms @subsection Using gnatxref with vi @code{gnatxref} can generate a tags file output, which can be used directly from @command{vi}. Note that the standard version of @command{vi} will not work properly with overloaded symbols. Consider using another free implementation of @command{vi}, such as @command{vim}. @smallexample $ gnatxref -v gnatfind.adb > tags @end smallexample @noindent will generate the tags file for @code{gnatfind} itself (if the sources are in the search path!). From @command{vi}, you can then use the command @samp{:tag @var{entity}} (replacing @var{entity} by whatever you are looking for), and vi will display a new file with the corresponding declaration of entity. @end ifclear @node Examples of gnatfind Usage @section Examples of @code{gnatfind} Usage @table @code @item gnatfind ^-f^/FULL_PATHNAME^ xyz:main.adb Find declarations for all entities xyz referenced at least once in main.adb. The references are search in every library file in the search path. The directories will be printed as well (as the @samp{^-f^/FULL_PATHNAME^} switch is set) The output will look like: @smallexample ^directory/^[directory]^main.ads:106:14: xyz <= declaration ^directory/^[directory]^main.adb:24:10: xyz <= body ^directory/^[directory]^foo.ads:45:23: xyz <= declaration @end smallexample @noindent that is to say, one of the entities xyz found in main.adb is declared at line 12 of main.ads (and its body is in main.adb), and another one is declared at line 45 of foo.ads @item gnatfind ^-fs^/FULL_PATHNAME/SOURCE_LINE^ xyz:main.adb This is the same command as the previous one, instead @code{gnatfind} will display the content of the Ada source file lines. The output will look like: @smallexample ^directory/^[directory]^main.ads:106:14: xyz <= declaration procedure xyz; ^directory/^[directory]^main.adb:24:10: xyz <= body procedure xyz is ^directory/^[directory]^foo.ads:45:23: xyz <= declaration xyz : Integer; @end smallexample @noindent This can make it easier to find exactly the location your are looking for. @item gnatfind ^-r^/REFERENCES^ "*x*":main.ads:123 foo.adb Find references to all entities containing an x that are referenced on line 123 of main.ads. The references will be searched only in main.ads and foo.adb. @item gnatfind main.ads:123 Find declarations and bodies for all entities that are referenced on line 123 of main.ads. This is the same as @code{gnatfind "*":main.adb:123}. @item gnatfind ^mydir/^[mydir]^main.adb:123:45 Find the declaration for the entity referenced at column 45 in line 123 of file main.adb in directory mydir. Note that it is usual to omit the identifier name when the column is given, since the column position identifies a unique reference. The column has to be the beginning of the identifier, and should not point to any character in the middle of the identifier. @end table @c ********************************* @node The GNAT Pretty-Printer gnatpp @chapter The GNAT Pretty-Printer @command{gnatpp} @findex gnatpp @cindex Pretty-Printer @noindent ^The @command{gnatpp} tool^GNAT PRETTY^ is an ASIS-based utility for source reformatting / pretty-printing. It takes an Ada source file as input and generates a reformatted version as output. You can specify various style directives via switches; e.g., identifier case conventions, rules of indentation, and comment layout. To produce a reformatted file, @command{gnatpp} generates and uses the ASIS tree for the input source and thus requires the input to be syntactically and semantically legal. If this condition is not met, @command{gnatpp} will terminate with an error message; no output file will be generated. If the source files presented to @command{gnatpp} contain preprocessing directives, then the output file will correspond to the generated source after all preprocessing is carried out. There is no way using @command{gnatpp} to obtain pretty printed files that include the preprocessing directives. If the compilation unit contained in the input source depends semantically upon units located outside the current directory, you have to provide the source search path when invoking @command{gnatpp}, if these units are contained in files with names that do not follow the GNAT file naming rules, you have to provide the configuration file describing the corresponding naming scheme; see the description of the @command{gnatpp} switches below. Another possibility is to use a project file and to call @command{gnatpp} through the @command{gnat} driver The @command{gnatpp} command has the form @smallexample @c $ gnatpp @ovar{switches} @var{filename} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatpp @r{[}@var{switches}@r{]} @var{filename} @r{[}-cargs @var{gcc_switches}@r{]} @end smallexample @noindent where @itemize @bullet @item @var{switches} is an optional sequence of switches defining such properties as the formatting rules, the source search path, and the destination for the output source file @item @var{filename} is the name (including the extension) of the source file to reformat; ``wildcards'' or several file names on the same gnatpp command are allowed. The file name may contain path information; it does not have to follow the GNAT file naming rules @item @samp{@var{gcc_switches}} is a list of switches for @command{gcc}. They will be passed on to all compiler invocations made by @command{gnatelim} to generate the ASIS trees. Here you can provide @option{^-I^/INCLUDE_DIRS=^} switches to form the source search path, use the @option{-gnatec} switch to set the configuration file, use the @option{-gnat05} switch if sources should be compiled in Ada 2005 mode etc. @end itemize @menu * Switches for gnatpp:: * Formatting Rules:: @end menu @node Switches for gnatpp @section Switches for @command{gnatpp} @noindent The following subsections describe the various switches accepted by @command{gnatpp}, organized by category. @ifclear vms You specify a switch by supplying a name and generally also a value. In many cases the values for a switch with a given name are incompatible with each other (for example the switch that controls the casing of a reserved word may have exactly one value: upper case, lower case, or mixed case) and thus exactly one such switch can be in effect for an invocation of @command{gnatpp}. If more than one is supplied, the last one is used. However, some values for the same switch are mutually compatible. You may supply several such switches to @command{gnatpp}, but then each must be specified in full, with both the name and the value. Abbreviated forms (the name appearing once, followed by each value) are not permitted. For example, to set the alignment of the assignment delimiter both in declarations and in assignment statements, you must write @option{-A2A3} (or @option{-A2 -A3}), but not @option{-A23}. @end ifclear @ifset vms In many cases the set of options for a given qualifier are incompatible with each other (for example the qualifier that controls the casing of a reserved word may have exactly one option, which specifies either upper case, lower case, or mixed case), and thus exactly one such option can be in effect for an invocation of @command{gnatpp}. If more than one is supplied, the last one is used. However, some qualifiers have options that are mutually compatible, and then you may then supply several such options when invoking @command{gnatpp}. @end ifset In most cases, it is obvious whether or not the ^values for a switch with a given name^options for a given qualifier^ are compatible with each other. When the semantics might not be evident, the summaries below explicitly indicate the effect. @menu * Alignment Control:: * Casing Control:: * Construct Layout Control:: * General Text Layout Control:: * Other Formatting Options:: * Setting the Source Search Path:: * Output File Control:: * Other gnatpp Switches:: @end menu @node Alignment Control @subsection Alignment Control @cindex Alignment control in @command{gnatpp} @noindent Programs can be easier to read if certain constructs are vertically aligned. By default all alignments are set ON. Through the @option{^-A0^/ALIGN=OFF^} switch you may reset the default to OFF, and then use one or more of the other ^@option{-A@var{n}} switches^@option{/ALIGN} options^ to activate alignment for specific constructs. @table @option @cindex @option{^-A@var{n}^/ALIGN^} (@command{gnatpp}) @ifset vms @item /ALIGN=ON Set all alignments to ON @end ifset @item ^-A0^/ALIGN=OFF^ Set all alignments to OFF @item ^-A1^/ALIGN=COLONS^ Align @code{:} in declarations @item ^-A2^/ALIGN=DECLARATIONS^ Align @code{:=} in initializations in declarations @item ^-A3^/ALIGN=STATEMENTS^ Align @code{:=} in assignment statements @item ^-A4^/ALIGN=ARROWS^ Align @code{=>} in associations @item ^-A5^/ALIGN=COMPONENT_CLAUSES^ Align @code{at} keywords in the component clauses in record representation clauses @end table @noindent The @option{^-A^/ALIGN^} switches are mutually compatible; any combination is allowed. @node Casing Control @subsection Casing Control @cindex Casing control in @command{gnatpp} @noindent @command{gnatpp} allows you to specify the casing for reserved words, pragma names, attribute designators and identifiers. For identifiers you may define a general rule for name casing but also override this rule via a set of dictionary files. Three types of casing are supported: lower case, upper case, and mixed case. Lower and upper case are self-explanatory (but since some letters in Latin1 and other GNAT-supported character sets exist only in lower-case form, an upper case conversion will have no effect on them.) ``Mixed case'' means that the first letter, and also each letter immediately following an underscore, are converted to their uppercase forms; all the other letters are converted to their lowercase forms. @table @option @cindex @option{^-a@var{x}^/ATTRIBUTE^} (@command{gnatpp}) @item ^-aL^/ATTRIBUTE_CASING=LOWER_CASE^ Attribute designators are lower case @item ^-aU^/ATTRIBUTE_CASING=UPPER_CASE^ Attribute designators are upper case @item ^-aM^/ATTRIBUTE_CASING=MIXED_CASE^ Attribute designators are mixed case (this is the default) @cindex @option{^-k@var{x}^/KEYWORD_CASING^} (@command{gnatpp}) @item ^-kL^/KEYWORD_CASING=LOWER_CASE^ Keywords (technically, these are known in Ada as @emph{reserved words}) are lower case (this is the default) @item ^-kU^/KEYWORD_CASING=UPPER_CASE^ Keywords are upper case @cindex @option{^-n@var{x}^/NAME_CASING^} (@command{gnatpp}) @item ^-nD^/NAME_CASING=AS_DECLARED^ Name casing for defining occurrences are as they appear in the source file (this is the default) @item ^-nU^/NAME_CASING=UPPER_CASE^ Names are in upper case @item ^-nL^/NAME_CASING=LOWER_CASE^ Names are in lower case @item ^-nM^/NAME_CASING=MIXED_CASE^ Names are in mixed case @cindex @option{^-p@var{x}^/PRAGMA_CASING^} (@command{gnatpp}) @item ^-pL^/PRAGMA_CASING=LOWER_CASE^ Pragma names are lower case @item ^-pU^/PRAGMA_CASING=UPPER_CASE^ Pragma names are upper case @item ^-pM^/PRAGMA_CASING=MIXED_CASE^ Pragma names are mixed case (this is the default) @item ^-D@var{file}^/DICTIONARY=@var{file}^ @cindex @option{^-D^/DICTIONARY^} (@command{gnatpp}) Use @var{file} as a @emph{dictionary file} that defines the casing for a set of specified names, thereby overriding the effect on these names by any explicit or implicit ^-n^/NAME_CASING^ switch. To supply more than one dictionary file, use ^several @option{-D} switches^a list of files as options^. @noindent @option{gnatpp} implicitly uses a @emph{default dictionary file} to define the casing for the Ada predefined names and the names declared in the GNAT libraries. @item ^-D-^/SPECIFIC_CASING^ @cindex @option{^-D-^/SPECIFIC_CASING^} (@command{gnatpp}) Do not use the default dictionary file; instead, use the casing defined by a @option{^-n^/NAME_CASING^} switch and any explicit dictionary file(s) @end table @noindent The structure of a dictionary file, and details on the conventions used in the default dictionary file, are defined in @ref{Name Casing}. The @option{^-D-^/SPECIFIC_CASING^} and @option{^-D@var{file}^/DICTIONARY=@var{file}^} switches are mutually compatible. @node Construct Layout Control @subsection Construct Layout Control @cindex Layout control in @command{gnatpp} @noindent This group of @command{gnatpp} switches controls the layout of comments and complex syntactic constructs. See @ref{Formatting Comments} for details on their effect. @table @option @cindex @option{^-c@var{n}^/COMMENTS_LAYOUT^} (@command{gnatpp}) @item ^-c0^/COMMENTS_LAYOUT=UNTOUCHED^ All the comments remain unchanged @item ^-c1^/COMMENTS_LAYOUT=DEFAULT^ GNAT-style comment line indentation (this is the default). @item ^-c2^/COMMENTS_LAYOUT=STANDARD_INDENT^ Reference-manual comment line indentation. @item ^-c3^/COMMENTS_LAYOUT=GNAT_BEGINNING^ GNAT-style comment beginning @item ^-c4^/COMMENTS_LAYOUT=REFORMAT^ Reformat comment blocks @item ^-c5^/COMMENTS_LAYOUT=KEEP_SPECIAL^ Keep unchanged special form comments Reformat comment blocks @cindex @option{^-l@var{n}^/CONSTRUCT_LAYOUT^} (@command{gnatpp}) @item ^-l1^/CONSTRUCT_LAYOUT=GNAT^ GNAT-style layout (this is the default) @item ^-l2^/CONSTRUCT_LAYOUT=COMPACT^ Compact layout @item ^-l3^/CONSTRUCT_LAYOUT=UNCOMPACT^ Uncompact layout @cindex @option{^-N^/NOTABS^} (@command{gnatpp}) @item ^-N^/NOTABS^ All the VT characters are removed from the comment text. All the HT characters are expanded with the sequences of space characters to get to the next tab stops. @cindex @option{^--no-separate-is^/NO_SEPARATE_IS^} (@command{gnatpp}) @item ^--no-separate-is^/NO_SEPARATE_IS^ Do not place the keyword @code{is} on a separate line in a subprogram body in case if the spec occupies more then one line. @cindex @option{^--separate-label^/SEPARATE_LABEL^} (@command{gnatpp}) @item ^--separate-label^/SEPARATE_LABEL^ Place statement label(s) on a separate line, with the following statement on the next line. @cindex @option{^--separate-loop-then^/SEPARATE_LOOP_THEN^} (@command{gnatpp}) @item ^--separate-loop-then^/SEPARATE_LOOP_THEN^ Place the keyword @code{loop} in FOR and WHILE loop statements and the keyword @code{then} in IF statements on a separate line. @cindex @option{^--no-separate-loop-then^/NO_SEPARATE_LOOP_THEN^} (@command{gnatpp}) @item ^--no-separate-loop-then^/NO_SEPARATE_LOOP_THEN^ Do not place the keyword @code{loop} in FOR and WHILE loop statements and the keyword @code{then} in IF statements on a separate line. This option is incompatible with @option{^--separate-loop-then^/SEPARATE_LOOP_THEN^} option. @cindex @option{^--use-on-new-line^/USE_ON_NEW_LINE^} (@command{gnatpp}) @item ^--use-on-new-line^/USE_ON_NEW_LINE^ Start each USE clause in a context clause from a separate line. @cindex @option{^--separate-stmt-name^/STMT_NAME_ON_NEW_LINE^} (@command{gnatpp}) @item ^--separate-stmt-name^/STMT_NAME_ON_NEW_LINE^ Use a separate line for a loop or block statement name, but do not use an extra indentation level for the statement itself. @end table @ifclear vms @noindent The @option{-c1} and @option{-c2} switches are incompatible. The @option{-c3} and @option{-c4} switches are compatible with each other and also with @option{-c1} and @option{-c2}. The @option{-c0} switch disables all the other comment formatting switches. The @option{-l1}, @option{-l2}, and @option{-l3} switches are incompatible. @end ifclear @ifset vms @noindent For the @option{/COMMENTS_LAYOUT} qualifier: @itemize @bullet @item The @option{DEFAULT} and @option{STANDARD_INDENT} options are incompatible. @item The @option{GNAT_BEGINNING} and @option{REFORMAT} options are compatible with each other and also with @option{DEFAULT} and @option{STANDARD_INDENT}. @end itemize @noindent The @option{GNAT}, @option{COMPACT}, and @option{UNCOMPACT} options for the @option{/CONSTRUCT_LAYOUT} qualifier are incompatible. @end ifset @node General Text Layout Control @subsection General Text Layout Control @noindent These switches allow control over line length and indentation. @table @option @item ^-M@var{nnn}^/LINE_LENGTH_MAX=@var{nnn}^ @cindex @option{^-M^/LINE_LENGTH^} (@command{gnatpp}) Maximum line length, @var{nnn} from 32@dots{}256, the default value is 79 @item ^-i@var{nnn}^/INDENTATION_LEVEL=@var{nnn}^ @cindex @option{^-i^/INDENTATION_LEVEL^} (@command{gnatpp}) Indentation level, @var{nnn} from 1@dots{}9, the default value is 3 @item ^-cl@var{nnn}^/CONTINUATION_INDENT=@var{nnn}^ @cindex @option{^-cl^/CONTINUATION_INDENT^} (@command{gnatpp}) Indentation level for continuation lines (relative to the line being continued), @var{nnn} from 1@dots{}9. The default value is one less then the (normal) indentation level, unless the indentation is set to 1 (in which case the default value for continuation line indentation is also 1) @end table @node Other Formatting Options @subsection Other Formatting Options @noindent These switches control the inclusion of missing end/exit labels, and the indentation level in @b{case} statements. @table @option @item ^-e^/NO_MISSED_LABELS^ @cindex @option{^-e^/NO_MISSED_LABELS^} (@command{gnatpp}) Do not insert missing end/exit labels. An end label is the name of a construct that may optionally be repeated at the end of the construct's declaration; e.g., the names of packages, subprograms, and tasks. An exit label is the name of a loop that may appear as target of an exit statement within the loop. By default, @command{gnatpp} inserts these end/exit labels when they are absent from the original source. This option suppresses such insertion, so that the formatted source reflects the original. @item ^-ff^/FORM_FEED_AFTER_PRAGMA_PAGE^ @cindex @option{^-ff^/FORM_FEED_AFTER_PRAGMA_PAGE^} (@command{gnatpp}) Insert a Form Feed character after a pragma Page. @item ^-T@var{nnn}^/MAX_INDENT=@var{nnn}^ @cindex @option{^-T^/MAX_INDENT^} (@command{gnatpp}) Do not use an additional indentation level for @b{case} alternatives and variants if there are @var{nnn} or more (the default value is 10). If @var{nnn} is 0, an additional indentation level is used for @b{case} alternatives and variants regardless of their number. @end table @node Setting the Source Search Path @subsection Setting the Source Search Path @noindent To define the search path for the input source file, @command{gnatpp} uses the same switches as the GNAT compiler, with the same effects. @table @option @item ^-I^/SEARCH=^@var{dir} @cindex @option{^-I^/SEARCH^} (@code{gnatpp}) The same as the corresponding gcc switch @item ^-I-^/NOCURRENT_DIRECTORY^ @cindex @option{^-I-^/NOCURRENT_DIRECTORY^} (@code{gnatpp}) The same as the corresponding gcc switch @item ^-gnatec^/CONFIGURATION_PRAGMAS_FILE^=@var{path} @cindex @option{^-gnatec^/CONFIGURATION_PRAGMAS_FILE^} (@code{gnatpp}) The same as the corresponding gcc switch @item ^--RTS^/RUNTIME_SYSTEM^=@var{path} @cindex @option{^--RTS^/RUNTIME_SYSTEM^} (@code{gnatpp}) The same as the corresponding gcc switch @end table @node Output File Control @subsection Output File Control @noindent By default the output is sent to the file whose name is obtained by appending the ^@file{.pp}^@file{$PP}^ suffix to the name of the input file (if the file with this name already exists, it is unconditionally overwritten). Thus if the input file is @file{^my_ada_proc.adb^MY_ADA_PROC.ADB^} then @command{gnatpp} will produce @file{^my_ada_proc.adb.pp^MY_ADA_PROC.ADB$PP^} as output file. The output may be redirected by the following switches: @table @option @item ^-pipe^/STANDARD_OUTPUT^ @cindex @option{^-pipe^/STANDARD_OUTPUT^} (@code{gnatpp}) Send the output to @code{Standard_Output} @item ^-o @var{output_file}^/OUTPUT=@var{output_file}^ @cindex @option{^-o^/OUTPUT^} (@code{gnatpp}) Write the output into @var{output_file}. If @var{output_file} already exists, @command{gnatpp} terminates without reading or processing the input file. @item ^-of ^/FORCED_OUTPUT=^@var{output_file} @cindex @option{^-of^/FORCED_OUTPUT^} (@code{gnatpp}) Write the output into @var{output_file}, overwriting the existing file (if one is present). @item ^-r^/REPLACE^ @cindex @option{^-r^/REPLACE^} (@code{gnatpp}) Replace the input source file with the reformatted output, and copy the original input source into the file whose name is obtained by appending the ^@file{.npp}^@file{$NPP}^ suffix to the name of the input file. If a file with this name already exists, @command{gnatpp} terminates without reading or processing the input file. @item ^-rf^/OVERRIDING_REPLACE^ @cindex @option{^-rf^/OVERRIDING_REPLACE^} (@code{gnatpp}) Like @option{^-r^/REPLACE^} except that if the file with the specified name already exists, it is overwritten. @item ^-rnb^/REPLACE_NO_BACKUP^ @cindex @option{^-rnb^/REPLACE_NO_BACKUP^} (@code{gnatpp}) Replace the input source file with the reformatted output without creating any backup copy of the input source. @item ^--eol=@var{xxx}^/END_OF_LINE=@var{xxx}^ @cindex @option{^--eol^/END_OF_LINE^} (@code{gnatpp}) Specifies the format of the reformatted output file. The @var{xxx} ^string specified with the switch^option^ may be either @itemize @bullet @item ``@option{^dos^DOS^}'' MS DOS style, lines end with CR LF characters @item ``@option{^crlf^CRLF^}'' the same as @option{^crlf^CRLF^} @item ``@option{^unix^UNIX^}'' UNIX style, lines end with LF character @item ``@option{^lf^LF^}'' the same as @option{^unix^UNIX^} @end itemize @item ^-W^/RESULT_ENCODING=^@var{e} @cindex @option{^-W^/RESULT_ENCODING=^} (@command{gnatpp}) Specify the wide character encoding method used to write the code in the result file @var{e} is one of the following: @itemize @bullet @item ^h^HEX^ Hex encoding @item ^u^UPPER^ Upper half encoding @item ^s^SHIFT_JIS^ Shift/JIS encoding @item ^e^EUC^ EUC encoding @item ^8^UTF8^ UTF-8 encoding @item ^b^BRACKETS^ Brackets encoding (default value) @end itemize @end table @noindent Options @option{^-pipe^/STANDARD_OUTPUT^}, @option{^-o^/OUTPUT^} and @option{^-of^/FORCED_OUTPUT^} are allowed only if the call to gnatpp contains only one file to reformat. Option @option{^--eol^/END_OF_LINE^} and @option{^-W^/RESULT_ENCODING^} cannot be used together with @option{^-pipe^/STANDARD_OUTPUT^} option. @node Other gnatpp Switches @subsection Other @code{gnatpp} Switches @noindent The additional @command{gnatpp} switches are defined in this subsection. @table @option @item ^-files @var{filename}^/FILES=@var{filename}^ @cindex @option{^-files^/FILES^} (@code{gnatpp}) Take the argument source files from the specified file. This file should be an ordinary text file containing file names separated by spaces or line breaks. You can use this switch more than once in the same call to @command{gnatpp}. You also can combine this switch with an explicit list of files. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@code{gnatpp}) Verbose mode; @command{gnatpp} generates version information and then a trace of the actions it takes to produce or obtain the ASIS tree. @item ^-w^/WARNINGS^ @cindex @option{^-w^/WARNINGS^} (@code{gnatpp}) Warning mode; @command{gnatpp} generates a warning whenever it cannot provide a required layout in the result source. @end table @node Formatting Rules @section Formatting Rules @noindent The following subsections show how @command{gnatpp} treats ``white space'', comments, program layout, and name casing. They provide the detailed descriptions of the switches shown above. @menu * White Space and Empty Lines:: * Formatting Comments:: * Construct Layout:: * Name Casing:: @end menu @node White Space and Empty Lines @subsection White Space and Empty Lines @noindent @command{gnatpp} does not have an option to control space characters. It will add or remove spaces according to the style illustrated by the examples in the @cite{Ada Reference Manual}. The only format effectors (see @cite{Ada Reference Manual}, paragraph 2.1(13)) that will appear in the output file are platform-specific line breaks, and also format effectors within (but not at the end of) comments. In particular, each horizontal tab character that is not inside a comment will be treated as a space and thus will appear in the output file as zero or more spaces depending on the reformatting of the line in which it appears. The only exception is a Form Feed character, which is inserted after a pragma @code{Page} when @option{-ff} is set. The output file will contain no lines with trailing ``white space'' (spaces, format effectors). Empty lines in the original source are preserved only if they separate declarations or statements. In such contexts, a sequence of two or more empty lines is replaced by exactly one empty line. Note that a blank line will be removed if it separates two ``comment blocks'' (a comment block is a sequence of whole-line comments). In order to preserve a visual separation between comment blocks, use an ``empty comment'' (a line comprising only hyphens) rather than an empty line. Likewise, if for some reason you wish to have a sequence of empty lines, use a sequence of empty comments instead. @node Formatting Comments @subsection Formatting Comments @noindent Comments in Ada code are of two kinds: @itemize @bullet @item a @emph{whole-line comment}, which appears by itself (possibly preceded by ``white space'') on a line @item an @emph{end-of-line comment}, which follows some other Ada lexical element on the same line. @end itemize @noindent The indentation of a whole-line comment is that of either the preceding or following line in the formatted source, depending on switch settings as will be described below. For an end-of-line comment, @command{gnatpp} leaves the same number of spaces between the end of the preceding Ada lexical element and the beginning of the comment as appear in the original source, unless either the comment has to be split to satisfy the line length limitation, or else the next line contains a whole line comment that is considered a continuation of this end-of-line comment (because it starts at the same position). In the latter two cases, the start of the end-of-line comment is moved right to the nearest multiple of the indentation level. This may result in a ``line overflow'' (the right-shifted comment extending beyond the maximum line length), in which case the comment is split as described below. There is a difference between @option{^-c1^/COMMENTS_LAYOUT=DEFAULT^} (GNAT-style comment line indentation) and @option{^-c2^/COMMENTS_LAYOUT=STANDARD_INDENT^} (reference-manual comment line indentation). With reference-manual style, a whole-line comment is indented as if it were a declaration or statement at the same place (i.e., according to the indentation of the preceding line(s)). With GNAT style, a whole-line comment that is immediately followed by an @b{if} or @b{case} statement alternative, a record variant, or the reserved word @b{begin}, is indented based on the construct that follows it. For example: @smallexample @c ada @cartouche if A then null; -- some comment else null; end if; @end cartouche @end smallexample @noindent Reference-manual indentation produces: @smallexample @c ada @cartouche if A then null; -- some comment else null; end if; @end cartouche @end smallexample @noindent while GNAT-style indentation produces: @smallexample @c ada @cartouche if A then null; -- some comment else null; end if; @end cartouche @end smallexample @noindent The @option{^-c3^/COMMENTS_LAYOUT=GNAT_BEGINNING^} switch (GNAT style comment beginning) has the following effect: @itemize @bullet @item For each whole-line comment that does not end with two hyphens, @command{gnatpp} inserts spaces if necessary after the starting two hyphens to ensure that there are at least two spaces between these hyphens and the first non-blank character of the comment. @end itemize @noindent For an end-of-line comment, if in the original source the next line is a whole-line comment that starts at the same position as the end-of-line comment, then the whole-line comment (and all whole-line comments that follow it and that start at the same position) will start at this position in the output file. @noindent That is, if in the original source we have: @smallexample @c ada @cartouche begin A := B + C; -- B must be in the range Low1..High1 -- C must be in the range Low2..High2 --B+C will be in the range Low1+Low2..High1+High2 X := X + 1; @end cartouche @end smallexample @noindent Then in the formatted source we get @smallexample @c ada @cartouche begin A := B + C; -- B must be in the range Low1..High1 -- C must be in the range Low2..High2 -- B+C will be in the range Low1+Low2..High1+High2 X := X + 1; @end cartouche @end smallexample @noindent A comment that exceeds the line length limit will be split. Unless switch @option{^-c4^/COMMENTS_LAYOUT=REFORMAT^} (reformat comment blocks) is set and the line belongs to a reformattable block, splitting the line generates a @command{gnatpp} warning. The @option{^-c4^/COMMENTS_LAYOUT=REFORMAT^} switch specifies that whole-line comments may be reformatted in typical word processor style (that is, moving words between lines and putting as many words in a line as possible). @noindent The @option{^-c5^/COMMENTS_LAYOUT=KEEP_SPECIAL^} switch specifies, that comments that has a special format (that is, a character that is neither a letter nor digit not white space nor line break immediately following the leading @code{--} of the comment) should be without any change moved from the argument source into reformatted source. This switch allows to preserve comments that are used as a special marks in the code (e.g.@: SPARK annotation). @node Construct Layout @subsection Construct Layout @noindent In several cases the suggested layout in the Ada Reference Manual includes an extra level of indentation that many programmers prefer to avoid. The affected cases include: @itemize @bullet @item Record type declaration (RM 3.8) @item Record representation clause (RM 13.5.1) @item Loop statement in case if a loop has a statement identifier (RM 5.6) @item Block statement in case if a block has a statement identifier (RM 5.6) @end itemize @noindent In compact mode (when GNAT style layout or compact layout is set), the pretty printer uses one level of indentation instead of two. This is achieved in the record definition and record representation clause cases by putting the @code{record} keyword on the same line as the start of the declaration or representation clause, and in the block and loop case by putting the block or loop header on the same line as the statement identifier. @noindent The difference between GNAT style @option{^-l1^/CONSTRUCT_LAYOUT=GNAT^} and compact @option{^-l2^/CONSTRUCT_LAYOUT=COMPACT^} layout on the one hand, and uncompact layout @option{^-l3^/CONSTRUCT_LAYOUT=UNCOMPACT^} on the other hand, can be illustrated by the following examples: @iftex @cartouche @multitable @columnfractions .5 .5 @item @i{GNAT style, compact layout} @tab @i{Uncompact layout} @item @smallexample @c ada type q is record a : integer; b : integer; end record; @end smallexample @tab @smallexample @c ada type q is record a : integer; b : integer; end record; @end smallexample @item @smallexample @c ada for q use record a at 0 range 0 .. 31; b at 4 range 0 .. 31; end record; @end smallexample @tab @smallexample @c ada for q use record a at 0 range 0 .. 31; b at 4 range 0 .. 31; end record; @end smallexample @item @smallexample @c ada Block : declare A : Integer := 3; begin Proc (A, A); end Block; @end smallexample @tab @smallexample @c ada Block : declare A : Integer := 3; begin Proc (A, A); end Block; @end smallexample @item @smallexample @c ada Clear : for J in 1 .. 10 loop A (J) := 0; end loop Clear; @end smallexample @tab @smallexample @c ada Clear : for J in 1 .. 10 loop A (J) := 0; end loop Clear; @end smallexample @end multitable @end cartouche @end iftex @ifnottex @smallexample @cartouche GNAT style, compact layout Uncompact layout type q is record type q is a : integer; record b : integer; a : integer; end record; b : integer; end record; for q use record for q use a at 0 range 0 .. 31; record b at 4 range 0 .. 31; a at 0 range 0 .. 31; end record; b at 4 range 0 .. 31; end record; Block : declare Block : A : Integer := 3; declare begin A : Integer := 3; Proc (A, A); begin end Block; Proc (A, A); end Block; Clear : for J in 1 .. 10 loop Clear : A (J) := 0; for J in 1 .. 10 loop end loop Clear; A (J) := 0; end loop Clear; @end cartouche @end smallexample @end ifnottex @noindent A further difference between GNAT style layout and compact layout is that GNAT style layout inserts empty lines as separation for compound statements, return statements and bodies. Note that the layout specified by @option{^--separate-stmt-name^/STMT_NAME_ON_NEW_LINE^} for named block and loop statements overrides the layout defined by these constructs by @option{^-l1^/CONSTRUCT_LAYOUT=GNAT^}, @option{^-l2^/CONSTRUCT_LAYOUT=COMPACT^} or @option{^-l3^/CONSTRUCT_LAYOUT=UNCOMPACT^} option. @node Name Casing @subsection Name Casing @noindent @command{gnatpp} always converts the usage occurrence of a (simple) name to the same casing as the corresponding defining identifier. You control the casing for defining occurrences via the @option{^-n^/NAME_CASING^} switch. @ifclear vms With @option{-nD} (``as declared'', which is the default), @end ifclear @ifset vms With @option{/NAME_CASING=AS_DECLARED}, which is the default, @end ifset defining occurrences appear exactly as in the source file where they are declared. The other ^values for this switch^options for this qualifier^ --- @option{^-nU^UPPER_CASE^}, @option{^-nL^LOWER_CASE^}, @option{^-nM^MIXED_CASE^} --- result in ^upper, lower, or mixed case, respectively^the corresponding casing^. If @command{gnatpp} changes the casing of a defining occurrence, it analogously changes the casing of all the usage occurrences of this name. If the defining occurrence of a name is not in the source compilation unit currently being processed by @command{gnatpp}, the casing of each reference to this name is changed according to the value of the @option{^-n^/NAME_CASING^} switch (subject to the dictionary file mechanism described below). Thus @command{gnatpp} acts as though the @option{^-n^/NAME_CASING^} switch had affected the casing for the defining occurrence of the name. Some names may need to be spelled with casing conventions that are not covered by the upper-, lower-, and mixed-case transformations. You can arrange correct casing by placing such names in a @emph{dictionary file}, and then supplying a @option{^-D^/DICTIONARY^} switch. The casing of names from dictionary files overrides any @option{^-n^/NAME_CASING^} switch. To handle the casing of Ada predefined names and the names from GNAT libraries, @command{gnatpp} assumes a default dictionary file. The name of each predefined entity is spelled with the same casing as is used for the entity in the @cite{Ada Reference Manual}. The name of each entity in the GNAT libraries is spelled with the same casing as is used in the declaration of that entity. The @w{@option{^-D-^/SPECIFIC_CASING^}} switch suppresses the use of the default dictionary file. Instead, the casing for predefined and GNAT-defined names will be established by the @option{^-n^/NAME_CASING^} switch or explicit dictionary files. For example, by default the names @code{Ada.Text_IO} and @code{GNAT.OS_Lib} will appear as just shown, even in the presence of a @option{^-nU^/NAME_CASING=UPPER_CASE^} switch. To ensure that even such names are rendered in uppercase, additionally supply the @w{@option{^-D-^/SPECIFIC_CASING^}} switch (or else, less conveniently, place these names in upper case in a dictionary file). A dictionary file is a plain text file; each line in this file can be either a blank line (containing only space characters and ASCII.HT characters), an Ada comment line, or the specification of exactly one @emph{casing schema}. A casing schema is a string that has the following syntax: @smallexample @cartouche @var{casing_schema} ::= @var{identifier} | *@var{simple_identifier}* @var{simple_identifier} ::= @var{letter}@{@var{letter_or_digit}@} @end cartouche @end smallexample @noindent (See @cite{Ada Reference Manual}, Section 2.3) for the definition of the @var{identifier} lexical element and the @var{letter_or_digit} category.) The casing schema string can be followed by white space and/or an Ada-style comment; any amount of white space is allowed before the string. If a dictionary file is passed as @ifclear vms the value of a @option{-D@var{file}} switch @end ifclear @ifset vms an option to the @option{/DICTIONARY} qualifier @end ifset then for every simple name and every identifier, @command{gnatpp} checks if the dictionary defines the casing for the name or for some of its parts (the term ``subword'' is used below to denote the part of a name which is delimited by ``_'' or by the beginning or end of the word and which does not contain any ``_'' inside): @itemize @bullet @item if the whole name is in the dictionary, @command{gnatpp} uses for this name the casing defined by the dictionary; no subwords are checked for this word @item for every subword @command{gnatpp} checks if the dictionary contains the corresponding string of the form @code{*@var{simple_identifier}*}, and if it does, the casing of this @var{simple_identifier} is used for this subword @item if the whole name does not contain any ``_'' inside, and if for this name the dictionary contains two entries - one of the form @var{identifier}, and another - of the form *@var{simple_identifier}*, then the first one is applied to define the casing of this name @item if more than one dictionary file is passed as @command{gnatpp} switches, each dictionary adds new casing exceptions and overrides all the existing casing exceptions set by the previous dictionaries @item when @command{gnatpp} checks if the word or subword is in the dictionary, this check is not case sensitive @end itemize @noindent For example, suppose we have the following source to reformat: @smallexample @c ada @cartouche procedure test is name1 : integer := 1; name4_name3_name2 : integer := 2; name2_name3_name4 : Boolean; name1_var : Float; begin name2_name3_name4 := name4_name3_name2 > name1; end; @end cartouche @end smallexample @noindent And suppose we have two dictionaries: @smallexample @cartouche @i{dict1:} NAME1 *NaMe3* *Name1* @end cartouche @cartouche @i{dict2:} *NAME3* @end cartouche @end smallexample @noindent If @command{gnatpp} is called with the following switches: @smallexample @ifclear vms @command{gnatpp -nM -D dict1 -D dict2 test.adb} @end ifclear @ifset vms @command{gnatpp test.adb /NAME_CASING=MIXED_CASE /DICTIONARY=(dict1, dict2)} @end ifset @end smallexample @noindent then we will get the following name casing in the @command{gnatpp} output: @smallexample @c ada @cartouche procedure Test is NAME1 : Integer := 1; Name4_NAME3_Name2 : Integer := 2; Name2_NAME3_Name4 : Boolean; Name1_Var : Float; begin Name2_NAME3_Name4 := Name4_NAME3_Name2 > NAME1; end Test; @end cartouche @end smallexample @c ********************************* @node The GNAT Metric Tool gnatmetric @chapter The GNAT Metric Tool @command{gnatmetric} @findex gnatmetric @cindex Metric tool @noindent ^The @command{gnatmetric} tool^@command{GNAT METRIC}^ is an ASIS-based utility for computing various program metrics. It takes an Ada source file as input and generates a file containing the metrics data as output. Various switches control which metrics are computed and output. @command{gnatmetric} generates and uses the ASIS tree for the input source and thus requires the input to be syntactically and semantically legal. If this condition is not met, @command{gnatmetric} will generate an error message; no metric information for this file will be computed and reported. If the compilation unit contained in the input source depends semantically upon units in files located outside the current directory, you have to provide the source search path when invoking @command{gnatmetric}. If it depends semantically upon units that are contained in files with names that do not follow the GNAT file naming rules, you have to provide the configuration file describing the corresponding naming scheme (see the description of the @command{gnatmetric} switches below.) Alternatively, you may use a project file and invoke @command{gnatmetric} through the @command{gnat} driver. The @command{gnatmetric} command has the form @smallexample @c $ gnatmetric @ovar{switches} @{@var{filename}@} @r{[}-cargs @var{gcc_switches}@r{]} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatmetric @r{[}@var{switches}@r{]} @{@var{filename}@} @r{[}-cargs @var{gcc_switches}@r{]} @end smallexample @noindent where @itemize @bullet @item @var{switches} specify the metrics to compute and define the destination for the output @item Each @var{filename} is the name (including the extension) of a source file to process. ``Wildcards'' are allowed, and the file name may contain path information. If no @var{filename} is supplied, then the @var{switches} list must contain at least one @option{-files} switch (@pxref{Other gnatmetric Switches}). Including both a @option{-files} switch and one or more @var{filename} arguments is permitted. @item @samp{@var{gcc_switches}} is a list of switches for @command{gcc}. They will be passed on to all compiler invocations made by @command{gnatmetric} to generate the ASIS trees. Here you can provide @option{^-I^/INCLUDE_DIRS=^} switches to form the source search path, and use the @option{-gnatec} switch to set the configuration file, use the @option{-gnat05} switch if sources should be compiled in Ada 2005 mode etc. @end itemize @menu * Switches for gnatmetric:: @end menu @node Switches for gnatmetric @section Switches for @command{gnatmetric} @noindent The following subsections describe the various switches accepted by @command{gnatmetric}, organized by category. @menu * Output Files Control:: * Disable Metrics For Local Units:: * Specifying a set of metrics to compute:: * Other gnatmetric Switches:: * Generate project-wide metrics:: @end menu @node Output Files Control @subsection Output File Control @cindex Output file control in @command{gnatmetric} @noindent @command{gnatmetric} has two output formats. It can generate a textual (human-readable) form, and also XML. By default only textual output is generated. When generating the output in textual form, @command{gnatmetric} creates for each Ada source file a corresponding text file containing the computed metrics, except for the case when the set of metrics specified by gnatmetric parameters consists only of metrics that are computed for the whole set of analyzed sources, but not for each Ada source. By default, this file is placed in the same directory as where the source file is located, and its name is obtained by appending the ^@file{.metrix}^@file{$METRIX}^ suffix to the name of the input file. All the output information generated in XML format is placed in a single file. By default this file is placed in the current directory and has the name ^@file{metrix.xml}^@file{METRIX$XML}^. Some of the computed metrics are summed over the units passed to @command{gnatmetric}; for example, the total number of lines of code. By default this information is sent to @file{stdout}, but a file can be specified with the @option{-og} switch. The following switches control the @command{gnatmetric} output: @table @option @cindex @option{^-x^/XML^} (@command{gnatmetric}) @item ^-x^/XML^ Generate the XML output @cindex @option{^-xs^/XSD^} (@command{gnatmetric}) @item ^-xs^/XSD^ Generate the XML output and the XML schema file that describes the structure of the XML metric report, this schema is assigned to the XML file. The schema file has the same name as the XML output file with @file{.xml} suffix replaced with @file{.xsd} @cindex @option{^-nt^/NO_TEXT^} (@command{gnatmetric}) @item ^-nt^/NO_TEXT^ Do not generate the output in text form (implies @option{^-x^/XML^}) @cindex @option{^-d^/DIRECTORY^} (@command{gnatmetric}) @item ^-d @var{output_dir}^/DIRECTORY=@var{output_dir}^ Put text files with detailed metrics into @var{output_dir} @cindex @option{^-o^/SUFFIX_DETAILS^} (@command{gnatmetric}) @item ^-o @var{file_suffix}^/SUFFIX_DETAILS=@var{file_suffix}^ Use @var{file_suffix}, instead of ^@file{.metrix}^@file{$METRIX}^ in the name of the output file. @cindex @option{^-og^/GLOBAL_OUTPUT^} (@command{gnatmetric}) @item ^-og @var{file_name}^/GLOBAL_OUTPUT=@var{file_name}^ Put global metrics into @var{file_name} @cindex @option{^-ox^/XML_OUTPUT^} (@command{gnatmetric}) @item ^-ox @var{file_name}^/XML_OUTPUT=@var{file_name}^ Put the XML output into @var{file_name} (also implies @option{^-x^/XML^}) @cindex @option{^-sfn^/SHORT_SOURCE_FILE_NAME^} (@command{gnatmetric}) @item ^-sfn^/SHORT_SOURCE_FILE_NAME^ Use ``short'' source file names in the output. (The @command{gnatmetric} output includes the name(s) of the Ada source file(s) from which the metrics are computed. By default each name includes the absolute path. The @option{^-sfn^/SHORT_SOURCE_FILE_NAME^} switch causes @command{gnatmetric} to exclude all directory information from the file names that are output.) @end table @node Disable Metrics For Local Units @subsection Disable Metrics For Local Units @cindex Disable Metrics For Local Units in @command{gnatmetric} @noindent @command{gnatmetric} relies on the GNAT compilation model @minus{} one compilation unit per one source file. It computes line metrics for the whole source file, and it also computes syntax and complexity metrics for the file's outermost unit. By default, @command{gnatmetric} will also compute all metrics for certain kinds of locally declared program units: @itemize @bullet @item subprogram (and generic subprogram) bodies; @item package (and generic package) specs and bodies; @item task object and type specifications and bodies; @item protected object and type specifications and bodies. @end itemize @noindent These kinds of entities will be referred to as @emph{eligible local program units}, or simply @emph{eligible local units}, @cindex Eligible local unit (for @command{gnatmetric}) in the discussion below. Note that a subprogram declaration, generic instantiation, or renaming declaration only receives metrics computation when it appear as the outermost entity in a source file. Suppression of metrics computation for eligible local units can be obtained via the following switch: @table @option @cindex @option{^-n@var{x}^/SUPPRESS^} (@command{gnatmetric}) @item ^-nolocal^/SUPPRESS=LOCAL_DETAILS^ Do not compute detailed metrics for eligible local program units @end table @node Specifying a set of metrics to compute @subsection Specifying a set of metrics to compute @noindent By default all the metrics are computed and reported. The switches described in this subsection allow you to control, on an individual basis, whether metrics are computed and reported. If at least one positive metric switch is specified (that is, a switch that defines that a given metric or set of metrics is to be computed), then only explicitly specified metrics are reported. @menu * Line Metrics Control:: * Syntax Metrics Control:: * Complexity Metrics Control:: * Object-Oriented Metrics Control:: @end menu @node Line Metrics Control @subsubsection Line Metrics Control @cindex Line metrics control in @command{gnatmetric} @noindent For any (legal) source file, and for each of its eligible local program units, @command{gnatmetric} computes the following metrics: @itemize @bullet @item the total number of lines; @item the total number of code lines (i.e., non-blank lines that are not comments) @item the number of comment lines @item the number of code lines containing end-of-line comments; @item the comment percentage: the ratio between the number of lines that contain comments and the number of all non-blank lines, expressed as a percentage; @item the number of empty lines and lines containing only space characters and/or format effectors (blank lines) @item the average number of code lines in subprogram bodies, task bodies, entry bodies and statement sequences in package bodies (this metric is only computed across the whole set of the analyzed units) @end itemize @noindent @command{gnatmetric} sums the values of the line metrics for all the files being processed and then generates the cumulative results. The tool also computes for all the files being processed the average number of code lines in bodies. You can use the following switches to select the specific line metrics to be computed and reported. @table @option @cindex @option{^--lines@var{x}^/LINE_COUNT_METRICS^} (@command{gnatmetric}) @ifclear vms @cindex @option{--no-lines@var{x}} @end ifclear @item ^--lines-all^/LINE_COUNT_METRICS=ALL^ Report all the line metrics @item ^--no-lines-all^/LINE_COUNT_METRICS=NONE^ Do not report any of line metrics @item ^--lines^/LINE_COUNT_METRICS=ALL_LINES^ Report the number of all lines @item ^--no-lines^/LINE_COUNT_METRICS=NOALL_LINES^ Do not report the number of all lines @item ^--lines-code^/LINE_COUNT_METRICS=CODE_LINES^ Report the number of code lines @item ^--no-lines-code^/LINE_COUNT_METRICS=NOCODE_LINES^ Do not report the number of code lines @item ^--lines-comment^/LINE_COUNT_METRICS=COMMENT_LINES^ Report the number of comment lines @item ^--no-lines-comment^/LINE_COUNT_METRICS=NOCOMMENT_LINES^ Do not report the number of comment lines @item ^--lines-eol-comment^/LINE_COUNT_METRICS=CODE_COMMENT_LINES^ Report the number of code lines containing end-of-line comments @item ^--no-lines-eol-comment^/LINE_COUNT_METRICS=NOCODE_COMMENT_LINES^ Do not report the number of code lines containing end-of-line comments @item ^--lines-ratio^/LINE_COUNT_METRICS=COMMENT_PERCENTAGE^ Report the comment percentage in the program text @item ^--no-lines-ratio^/LINE_COUNT_METRICS=NOCOMMENT_PERCENTAGE^ Do not report the comment percentage in the program text @item ^--lines-blank^/LINE_COUNT_METRICS=BLANK_LINES^ Report the number of blank lines @item ^--no-lines-blank^/LINE_COUNT_METRICS=NOBLANK_LINES^ Do not report the number of blank lines @item ^--lines-average^/LINE_COUNT_METRICS=AVERAGE_BODY_LINES^ Report the average number of code lines in subprogram bodies, task bodies, entry bodies and statement sequences in package bodies. The metric is computed and reported for the whole set of processed Ada sources only. @item ^--no-lines-average^/LINE_COUNT_METRICS=NOAVERAGE_BODY_LINES^ Do not report the average number of code lines in subprogram bodies, task bodies, entry bodies and statement sequences in package bodies. @end table @node Syntax Metrics Control @subsubsection Syntax Metrics Control @cindex Syntax metrics control in @command{gnatmetric} @noindent @command{gnatmetric} computes various syntactic metrics for the outermost unit and for each eligible local unit: @table @emph @item LSLOC (``Logical Source Lines Of Code'') The total number of declarations and the total number of statements @item Maximal static nesting level of inner program units According to @cite{Ada Reference Manual}, 10.1(1), ``A program unit is either a package, a task unit, a protected unit, a protected entry, a generic unit, or an explicitly declared subprogram other than an enumeration literal.'' @item Maximal nesting level of composite syntactic constructs This corresponds to the notion of the maximum nesting level in the GNAT built-in style checks (@pxref{Style Checking}) @end table @noindent For the outermost unit in the file, @command{gnatmetric} additionally computes the following metrics: @table @emph @item Public subprograms This metric is computed for package specs. It is the number of subprograms and generic subprograms declared in the visible part (including the visible part of nested packages, protected objects, and protected types). @item All subprograms This metric is computed for bodies and subunits. The metric is equal to a total number of subprogram bodies in the compilation unit. Neither generic instantiations nor renamings-as-a-body nor body stubs are counted. Any subprogram body is counted, independently of its nesting level and enclosing constructs. Generic bodies and bodies of protected subprograms are counted in the same way as ``usual'' subprogram bodies. @item Public types This metric is computed for package specs and generic package declarations. It is the total number of types that can be referenced from outside this compilation unit, plus the number of types from all the visible parts of all the visible generic packages. Generic formal types are not counted. Only types, not subtypes, are included. @noindent Along with the total number of public types, the following types are counted and reported separately: @itemize @bullet @item Abstract types @item Root tagged types (abstract, non-abstract, private, non-private). Type extensions are @emph{not} counted @item Private types (including private extensions) @item Task types @item Protected types @end itemize @item All types This metric is computed for any compilation unit. It is equal to the total number of the declarations of different types given in the compilation unit. The private and the corresponding full type declaration are counted as one type declaration. Incomplete type declarations and generic formal types are not counted. No distinction is made among different kinds of types (abstract, private etc.); the total number of types is computed and reported. @end table @noindent By default, all the syntax metrics are computed and reported. You can use the following switches to select specific syntax metrics. @table @option @cindex @option{^--syntax@var{x}^/SYNTAX_METRICS^} (@command{gnatmetric}) @ifclear vms @cindex @option{--no-syntax@var{x}} (@command{gnatmetric}) @end ifclear @item ^--syntax-all^/SYNTAX_METRICS=ALL^ Report all the syntax metrics @item ^--no-syntax-all^/SYNTAX_METRICS=NONE^ Do not report any of syntax metrics @item ^--declarations^/SYNTAX_METRICS=DECLARATIONS^ Report the total number of declarations @item ^--no-declarations^/SYNTAX_METRICS=NODECLARATIONS^ Do not report the total number of declarations @item ^--statements^/SYNTAX_METRICS=STATEMENTS^ Report the total number of statements @item ^--no-statements^/SYNTAX_METRICS=NOSTATEMENTS^ Do not report the total number of statements @item ^--public-subprograms^/SYNTAX_METRICS=PUBLIC_SUBPROGRAMS^ Report the number of public subprograms in a compilation unit @item ^--no-public-subprograms^/SYNTAX_METRICS=NOPUBLIC_SUBPROGRAMS^ Do not report the number of public subprograms in a compilation unit @item ^--all-subprograms^/SYNTAX_METRICS=ALL_SUBPROGRAMS^ Report the number of all the subprograms in a compilation unit @item ^--no-all-subprograms^/SYNTAX_METRICS=NOALL_SUBPROGRAMS^ Do not report the number of all the subprograms in a compilation unit @item ^--public-types^/SYNTAX_METRICS=PUBLIC_TYPES^ Report the number of public types in a compilation unit @item ^--no-public-types^/SYNTAX_METRICS=NOPUBLIC_TYPES^ Do not report the number of public types in a compilation unit @item ^--all-types^/SYNTAX_METRICS=ALL_TYPES^ Report the number of all the types in a compilation unit @item ^--no-all-types^/SYNTAX_METRICS=NOALL_TYPES^ Do not report the number of all the types in a compilation unit @item ^--unit-nesting^/SYNTAX_METRICS=UNIT_NESTING^ Report the maximal program unit nesting level @item ^--no-unit-nesting^/SYNTAX_METRICS=UNIT_NESTING_OFF^ Do not report the maximal program unit nesting level @item ^--construct-nesting^/SYNTAX_METRICS=CONSTRUCT_NESTING^ Report the maximal construct nesting level @item ^--no-construct-nesting^/SYNTAX_METRICS=NOCONSTRUCT_NESTING^ Do not report the maximal construct nesting level @end table @node Complexity Metrics Control @subsubsection Complexity Metrics Control @cindex Complexity metrics control in @command{gnatmetric} @noindent For a program unit that is an executable body (a subprogram body (including generic bodies), task body, entry body or a package body containing its own statement sequence) @command{gnatmetric} computes the following complexity metrics: @itemize @bullet @item McCabe cyclomatic complexity; @item McCabe essential complexity; @item maximal loop nesting level @end itemize @noindent The McCabe complexity metrics are defined in @url{http://www.mccabe.com/pdf/nist235r.pdf} According to McCabe, both control statements and short-circuit control forms should be taken into account when computing cyclomatic complexity. For each body, we compute three metric values: @itemize @bullet @item the complexity introduced by control statements only, without taking into account short-circuit forms, @item the complexity introduced by short-circuit control forms only, and @item the total cyclomatic complexity, which is the sum of these two values. @end itemize @noindent When computing cyclomatic and essential complexity, @command{gnatmetric} skips the code in the exception handlers and in all the nested program units. By default, all the complexity metrics are computed and reported. For more fine-grained control you can use the following switches: @table @option @cindex @option{^-complexity@var{x}^/COMPLEXITY_METRICS^} (@command{gnatmetric}) @ifclear vms @cindex @option{--no-complexity@var{x}} @end ifclear @item ^--complexity-all^/COMPLEXITY_METRICS=ALL^ Report all the complexity metrics @item ^--no-complexity-all^/COMPLEXITY_METRICS=NONE^ Do not report any of complexity metrics @item ^--complexity-cyclomatic^/COMPLEXITY_METRICS=CYCLOMATIC^ Report the McCabe Cyclomatic Complexity @item ^--no-complexity-cyclomatic^/COMPLEXITY_METRICS=NOCYCLOMATIC^ Do not report the McCabe Cyclomatic Complexity @item ^--complexity-essential^/COMPLEXITY_METRICS=ESSENTIAL^ Report the Essential Complexity @item ^--no-complexity-essential^/COMPLEXITY_METRICS=NOESSENTIAL^ Do not report the Essential Complexity @item ^--loop-nesting^/COMPLEXITY_METRICS=LOOP_NESTING_ON^ Report maximal loop nesting level @item ^--no-loop-nesting^/COMPLEXITY_METRICS=NOLOOP_NESTING^ Do not report maximal loop nesting level @item ^--complexity-average^/COMPLEXITY_METRICS=AVERAGE_COMPLEXITY^ Report the average McCabe Cyclomatic Complexity for all the subprogram bodies, task bodies, entry bodies and statement sequences in package bodies. The metric is computed and reported for whole set of processed Ada sources only. @item ^--no-complexity-average^/COMPLEXITY_METRICS=NOAVERAGE_COMPLEXITY^ Do not report the average McCabe Cyclomatic Complexity for all the subprogram bodies, task bodies, entry bodies and statement sequences in package bodies @cindex @option{^-ne^/NO_EXITS_AS_GOTOS^} (@command{gnatmetric}) @item ^-ne^/NO_EXITS_AS_GOTOS^ Do not consider @code{exit} statements as @code{goto}s when computing Essential Complexity @item ^--extra-exit-points^/EXTRA_EXIT_POINTS^ Report the extra exit points for subprogram bodies. As an exit point, this metric counts @code{return} statements and raise statements in case when the raised exception is not handled in the same body. In case of a function this metric subtracts 1 from the number of exit points, because a function body must contain at least one @code{return} statement. @item ^--no-extra-exit-points^/NOEXTRA_EXIT_POINTS^ Do not report the extra exit points for subprogram bodies @end table @node Object-Oriented Metrics Control @subsubsection Object-Oriented Metrics Control @cindex Object-Oriented metrics control in @command{gnatmetric} @noindent @cindex Coupling metrics (in in @command{gnatmetric}) Coupling metrics are object-oriented metrics that measure the dependencies between a given class (or a group of classes) and the ``external world'' (that is, the other classes in the program). In this subsection the term ``class'' is used in its traditional object-oriented programming sense (an instantiable module that contains data and/or method members). A @emph{category} (of classes) is a group of closely related classes that are reused and/or modified together. A class @code{K}'s @emph{efferent coupling} is the number of classes that @code{K} depends upon. A category's efferent coupling is the number of classes outside the category that the classes inside the category depend upon. A class @code{K}'s @emph{afferent coupling} is the number of classes that depend upon @code{K}. A category's afferent coupling is the number of classes outside the category that depend on classes belonging to the category. Ada's implementation of the object-oriented paradigm does not use the traditional class notion, so the definition of the coupling metrics for Ada maps the class and class category notions onto Ada constructs. For the coupling metrics, several kinds of modules -- a library package, a library generic package, and a library generic package instantiation -- that define a tagged type or an interface type are considered to be a class. A category consists of a library package (or a library generic package) that defines a tagged or an interface type, together with all its descendant (generic) packages that define tagged or interface types. For any package counted as a class, its body and subunits (if any) are considered together with its spec when counting the dependencies, and coupling metrics are reported for spec units only. For dependencies between classes, the Ada semantic dependencies are considered. For coupling metrics, only dependencies on units that are considered as classes, are considered. When computing coupling metrics, @command{gnatmetric} counts only dependencies between units that are arguments of the gnatmetric call. Coupling metrics are program-wide (or project-wide) metrics, so to get a valid result, you should call @command{gnatmetric} for the whole set of sources that make up your program. It can be done by calling @command{gnatmetric} from the GNAT driver with @option{-U} option (see See @ref{The GNAT Driver and Project Files} for details. By default, all the coupling metrics are disabled. You can use the following switches to specify the coupling metrics to be computed and reported: @table @option @ifclear vms @cindex @option{--package@var{x}} (@command{gnatmetric}) @cindex @option{--no-package@var{x}} (@command{gnatmetric}) @cindex @option{--category@var{x}} (@command{gnatmetric}) @cindex @option{--no-category@var{x}} (@command{gnatmetric}) @end ifclear @ifset vms @cindex @option{/COUPLING_METRICS} (@command{gnatmetric}) @end ifset @item ^--coupling-all^/COUPLING_METRICS=ALL^ Report all the coupling metrics @item ^--no-coupling-all^/COUPLING_METRICS=NONE^ Do not report any of metrics @item ^--package-efferent-coupling^/COUPLING_METRICS=PACKAGE_EFFERENT^ Report package efferent coupling @item ^--no-package-efferent-coupling^/COUPLING_METRICS=NOPACKAGE_EFFERENT^ Do not report package efferent coupling @item ^--package-afferent-coupling^/COUPLING_METRICS=PACKAGE_AFFERENT^ Report package afferent coupling @item ^--no-package-afferent-coupling^/COUPLING_METRICS=NOPACKAGE_AFFERENT^ Do not report package afferent coupling @item ^--category-efferent-coupling^/COUPLING_METRICS=CATEGORY_EFFERENT^ Report category efferent coupling @item ^--no-category-efferent-coupling^/COUPLING_METRICS=NOCATEGORY_EFFERENT^ Do not report category efferent coupling @item ^--category-afferent-coupling^/COUPLING_METRICS=CATEGORY_AFFERENT^ Report category afferent coupling @item ^--no-category-afferent-coupling^/COUPLING_METRICS=NOCATEGORY_AFFERENT^ Do not report category afferent coupling @end table @node Other gnatmetric Switches @subsection Other @code{gnatmetric} Switches @noindent Additional @command{gnatmetric} switches are as follows: @table @option @item ^-files @var{filename}^/FILES=@var{filename}^ @cindex @option{^-files^/FILES^} (@code{gnatmetric}) Take the argument source files from the specified file. This file should be an ordinary text file containing file names separated by spaces or line breaks. You can use this switch more than once in the same call to @command{gnatmetric}. You also can combine this switch with an explicit list of files. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@code{gnatmetric}) Verbose mode; @command{gnatmetric} generates version information and then a trace of sources being processed. @item ^-dv^/DEBUG_OUTPUT^ @cindex @option{^-dv^/DEBUG_OUTPUT^} (@code{gnatmetric}) Debug mode; @command{gnatmetric} generates various messages useful to understand what happens during the metrics computation @item ^-q^/QUIET^ @cindex @option{^-q^/QUIET^} (@code{gnatmetric}) Quiet mode. @end table @node Generate project-wide metrics @subsection Generate project-wide metrics In order to compute metrics on all units of a given project, you can use the @command{gnat} driver along with the @option{-P} option: @smallexample gnat metric -Pproj @end smallexample @noindent If the project @code{proj} depends upon other projects, you can compute the metrics on the project closure using the @option{-U} option: @smallexample gnat metric -Pproj -U @end smallexample @noindent Finally, if not all the units are relevant to a particular main program in the project closure, you can generate metrics for the set of units needed to create a given main program (unit closure) using the @option{-U} option followed by the name of the main unit: @smallexample gnat metric -Pproj -U main @end smallexample @c *********************************** @node File Name Krunching Using gnatkr @chapter File Name Krunching Using @code{gnatkr} @findex gnatkr @noindent This chapter discusses the method used by the compiler to shorten the default file names chosen for Ada units so that they do not exceed the maximum length permitted. It also describes the @code{gnatkr} utility that can be used to determine the result of applying this shortening. @menu * About gnatkr:: * Using gnatkr:: * Krunching Method:: * Examples of gnatkr Usage:: @end menu @node About gnatkr @section About @code{gnatkr} @noindent The default file naming rule in GNAT is that the file name must be derived from the unit name. The exact default rule is as follows: @itemize @bullet @item Take the unit name and replace all dots by hyphens. @item If such a replacement occurs in the second character position of a name, and the first character is ^@samp{a}, @samp{g}, @samp{s}, or @samp{i}, ^@samp{A}, @samp{G}, @samp{S}, or @samp{I},^ then replace the dot by the character ^@samp{~} (tilde)^@samp{$} (dollar sign)^ instead of a minus. @end itemize The reason for this exception is to avoid clashes with the standard names for children of System, Ada, Interfaces, and GNAT, which use the prefixes ^@samp{s-}, @samp{a-}, @samp{i-}, and @samp{g-},^@samp{S-}, @samp{A-}, @samp{I-}, and @samp{G-},^ respectively. The @option{^-gnatk^/FILE_NAME_MAX_LENGTH=^@var{nn}} switch of the compiler activates a ``krunching'' circuit that limits file names to nn characters (where nn is a decimal integer). For example, using OpenVMS, where the maximum file name length is 39, the value of nn is usually set to 39, but if you want to generate a set of files that would be usable if ported to a system with some different maximum file length, then a different value can be specified. The default value of 39 for OpenVMS need not be specified. The @code{gnatkr} utility can be used to determine the krunched name for a given file, when krunched to a specified maximum length. @node Using gnatkr @section Using @code{gnatkr} @noindent The @code{gnatkr} command has the form @ifclear vms @smallexample @c $ gnatkr @var{name} @ovar{length} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatkr @var{name} @r{[}@var{length}@r{]} @end smallexample @end ifclear @ifset vms @smallexample $ gnatkr @var{name} /COUNT=nn @end smallexample @end ifset @noindent @var{name} is the uncrunched file name, derived from the name of the unit in the standard manner described in the previous section (i.e., in particular all dots are replaced by hyphens). The file name may or may not have an extension (defined as a suffix of the form period followed by arbitrary characters other than period). If an extension is present then it will be preserved in the output. For example, when krunching @file{hellofile.ads} to eight characters, the result will be hellofil.ads. Note: for compatibility with previous versions of @code{gnatkr} dots may appear in the name instead of hyphens, but the last dot will always be taken as the start of an extension. So if @code{gnatkr} is given an argument such as @file{Hello.World.adb} it will be treated exactly as if the first period had been a hyphen, and for example krunching to eight characters gives the result @file{hellworl.adb}. Note that the result is always all lower case (except on OpenVMS where it is all upper case). Characters of the other case are folded as required. @var{length} represents the length of the krunched name. The default when no argument is given is ^8^39^ characters. A length of zero stands for unlimited, in other words do not chop except for system files where the implied crunching length is always eight characters. @noindent The output is the krunched name. The output has an extension only if the original argument was a file name with an extension. @node Krunching Method @section Krunching Method @noindent The initial file name is determined by the name of the unit that the file contains. The name is formed by taking the full expanded name of the unit and replacing the separating dots with hyphens and using ^lowercase^uppercase^ for all letters, except that a hyphen in the second character position is replaced by a ^tilde^dollar sign^ if the first character is ^@samp{a}, @samp{i}, @samp{g}, or @samp{s}^@samp{A}, @samp{I}, @samp{G}, or @samp{S}^. The extension is @code{.ads} for a spec and @code{.adb} for a body. Krunching does not affect the extension, but the file name is shortened to the specified length by following these rules: @itemize @bullet @item The name is divided into segments separated by hyphens, tildes or underscores and all hyphens, tildes, and underscores are eliminated. If this leaves the name short enough, we are done. @item If the name is too long, the longest segment is located (left-most if there are two of equal length), and shortened by dropping its last character. This is repeated until the name is short enough. As an example, consider the krunching of @*@file{our-strings-wide_fixed.adb} to fit the name into 8 characters as required by some operating systems. @smallexample our-strings-wide_fixed 22 our strings wide fixed 19 our string wide fixed 18 our strin wide fixed 17 our stri wide fixed 16 our stri wide fixe 15 our str wide fixe 14 our str wid fixe 13 our str wid fix 12 ou str wid fix 11 ou st wid fix 10 ou st wi fix 9 ou st wi fi 8 Final file name: oustwifi.adb @end smallexample @item The file names for all predefined units are always krunched to eight characters. The krunching of these predefined units uses the following special prefix replacements: @table @file @item ada- replaced by @file{^a^A^-} @item gnat- replaced by @file{^g^G^-} @item interfaces- replaced by @file{^i^I^-} @item system- replaced by @file{^s^S^-} @end table These system files have a hyphen in the second character position. That is why normal user files replace such a character with a ^tilde^dollar sign^, to avoid confusion with system file names. As an example of this special rule, consider @*@file{ada-strings-wide_fixed.adb}, which gets krunched as follows: @smallexample ada-strings-wide_fixed 22 a- strings wide fixed 18 a- string wide fixed 17 a- strin wide fixed 16 a- stri wide fixed 15 a- stri wide fixe 14 a- str wide fixe 13 a- str wid fixe 12 a- str wid fix 11 a- st wid fix 10 a- st wi fix 9 a- st wi fi 8 Final file name: a-stwifi.adb @end smallexample @end itemize Of course no file shortening algorithm can guarantee uniqueness over all possible unit names, and if file name krunching is used then it is your responsibility to ensure that no name clashes occur. The utility program @code{gnatkr} is supplied for conveniently determining the krunched name of a file. @node Examples of gnatkr Usage @section Examples of @code{gnatkr} Usage @smallexample @iftex @leftskip=0cm @end iftex @ifclear vms $ gnatkr very_long_unit_name.ads --> velounna.ads $ gnatkr grandparent-parent-child.ads --> grparchi.ads $ gnatkr Grandparent.Parent.Child.ads --> grparchi.ads $ gnatkr grandparent-parent-child --> grparchi @end ifclear $ gnatkr very_long_unit_name.ads/count=6 --> vlunna.ads $ gnatkr very_long_unit_name.ads/count=0 --> very_long_unit_name.ads @end smallexample @node Preprocessing Using gnatprep @chapter Preprocessing Using @code{gnatprep} @findex gnatprep @noindent This chapter discusses how to use GNAT's @code{gnatprep} utility for simple preprocessing. Although designed for use with GNAT, @code{gnatprep} does not depend on any special GNAT features. For further discussion of conditional compilation in general, see @ref{Conditional Compilation}. @menu * Preprocessing Symbols:: * Using gnatprep:: * Switches for gnatprep:: * Form of Definitions File:: * Form of Input Text for gnatprep:: @end menu @node Preprocessing Symbols @section Preprocessing Symbols @noindent Preprocessing symbols are defined in definition files and referred to in sources to be preprocessed. A Preprocessing symbol is an identifier, following normal Ada (case-insensitive) rules for its syntax, with the restriction that all characters need to be in the ASCII set (no accented letters). @node Using gnatprep @section Using @code{gnatprep} @noindent To call @code{gnatprep} use @smallexample @c $ gnatprep @ovar{switches} @var{infile} @var{outfile} @ovar{deffile} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatprep @r{[}@var{switches}@r{]} @var{infile} @var{outfile} @r{[}@var{deffile}@r{]} @end smallexample @noindent where @table @var @item switches is an optional sequence of switches as described in the next section. @item infile is the full name of the input file, which is an Ada source file containing preprocessor directives. @item outfile is the full name of the output file, which is an Ada source in standard Ada form. When used with GNAT, this file name will normally have an ads or adb suffix. @item deffile is the full name of a text file containing definitions of preprocessing symbols to be referenced by the preprocessor. This argument is optional, and can be replaced by the use of the @option{-D} switch. @end table @node Switches for gnatprep @section Switches for @code{gnatprep} @table @option @c !sort! @item ^-b^/BLANK_LINES^ @cindex @option{^-b^/BLANK_LINES^} (@command{gnatprep}) Causes both preprocessor lines and the lines deleted by preprocessing to be replaced by blank lines in the output source file, preserving line numbers in the output file. @item ^-c^/COMMENTS^ @cindex @option{^-c^/COMMENTS^} (@command{gnatprep}) Causes both preprocessor lines and the lines deleted by preprocessing to be retained in the output source as comments marked with the special string @code{"--! "}. This option will result in line numbers being preserved in the output file. @item ^-C^/REPLACE_IN_COMMENTS^ @cindex @option{^-C^/REPLACE_IN_COMMENTS^} (@command{gnatprep}) Causes comments to be scanned. Normally comments are ignored by gnatprep. If this option is specified, then comments are scanned and any $symbol substitutions performed as in program text. This is particularly useful when structured comments are used (e.g., when writing programs in the SPARK dialect of Ada). Note that this switch is not available when doing integrated preprocessing (it would be useless in this context since comments are ignored by the compiler in any case). @item ^-Dsymbol=value^/ASSOCIATE="symbol=value"^ @cindex @option{^-D^/ASSOCIATE^} (@command{gnatprep}) Defines a new preprocessing symbol, associated with value. If no value is given on the command line, then symbol is considered to be @code{True}. This switch can be used in place of a definition file. @ifset vms @item /REMOVE @cindex @option{/REMOVE} (@command{gnatprep}) This is the default setting which causes lines deleted by preprocessing to be entirely removed from the output file. @end ifset @item ^-r^/REFERENCE^ @cindex @option{^-r^/REFERENCE^} (@command{gnatprep}) Causes a @code{Source_Reference} pragma to be generated that references the original input file, so that error messages will use the file name of this original file. The use of this switch implies that preprocessor lines are not to be removed from the file, so its use will force @option{^-b^/BLANK_LINES^} mode if @option{^-c^/COMMENTS^} has not been specified explicitly. Note that if the file to be preprocessed contains multiple units, then it will be necessary to @code{gnatchop} the output file from @code{gnatprep}. If a @code{Source_Reference} pragma is present in the preprocessed file, it will be respected by @code{gnatchop ^-r^/REFERENCE^} so that the final chopped files will correctly refer to the original input source file for @code{gnatprep}. @item ^-s^/SYMBOLS^ @cindex @option{^-s^/SYMBOLS^} (@command{gnatprep}) Causes a sorted list of symbol names and values to be listed on the standard output file. @item ^-u^/UNDEFINED^ @cindex @option{^-u^/UNDEFINED^} (@command{gnatprep}) Causes undefined symbols to be treated as having the value FALSE in the context of a preprocessor test. In the absence of this option, an undefined symbol in a @code{#if} or @code{#elsif} test will be treated as an error. @end table @ifclear vms @noindent Note: if neither @option{-b} nor @option{-c} is present, then preprocessor lines and deleted lines are completely removed from the output, unless -r is specified, in which case -b is assumed. @end ifclear @node Form of Definitions File @section Form of Definitions File @noindent The definitions file contains lines of the form @smallexample symbol := value @end smallexample @noindent where symbol is a preprocessing symbol, and value is one of the following: @itemize @bullet @item Empty, corresponding to a null substitution @item A string literal using normal Ada syntax @item Any sequence of characters from the set (letters, digits, period, underline). @end itemize @noindent Comment lines may also appear in the definitions file, starting with the usual @code{--}, and comments may be added to the definitions lines. @node Form of Input Text for gnatprep @section Form of Input Text for @code{gnatprep} @noindent The input text may contain preprocessor conditional inclusion lines, as well as general symbol substitution sequences. The preprocessor conditional inclusion commands have the form @smallexample @group @cartouche #if @i{expression} @r{[}then@r{]} lines #elsif @i{expression} @r{[}then@r{]} lines #elsif @i{expression} @r{[}then@r{]} lines @dots{} #else lines #end if; @end cartouche @end group @end smallexample @noindent In this example, @i{expression} is defined by the following grammar: @smallexample @i{expression} ::= @i{expression} ::= = "" @i{expression} ::= = @i{expression} ::= 'Defined @i{expression} ::= not @i{expression} @i{expression} ::= @i{expression} and @i{expression} @i{expression} ::= @i{expression} or @i{expression} @i{expression} ::= @i{expression} and then @i{expression} @i{expression} ::= @i{expression} or else @i{expression} @i{expression} ::= ( @i{expression} ) @end smallexample The following restriction exists: it is not allowed to have "and" or "or" following "not" in the same expression without parentheses. For example, this is not allowed: @smallexample not X or Y @end smallexample This should be one of the following: @smallexample (not X) or Y not (X or Y) @end smallexample @noindent For the first test (@i{expression} ::= ) the symbol must have either the value true or false, that is to say the right-hand of the symbol definition must be one of the (case-insensitive) literals @code{True} or @code{False}. If the value is true, then the corresponding lines are included, and if the value is false, they are excluded. The test (@i{expression} ::= @code{'Defined}) is true only if the symbol has been defined in the definition file or by a @option{-D} switch on the command line. Otherwise, the test is false. The equality tests are case insensitive, as are all the preprocessor lines. If the symbol referenced is not defined in the symbol definitions file, then the effect depends on whether or not switch @option{-u} is specified. If so, then the symbol is treated as if it had the value false and the test fails. If this switch is not specified, then it is an error to reference an undefined symbol. It is also an error to reference a symbol that is defined with a value other than @code{True} or @code{False}. The use of the @code{not} operator inverts the sense of this logical test. The @code{not} operator cannot be combined with the @code{or} or @code{and} operators, without parentheses. For example, "if not X or Y then" is not allowed, but "if (not X) or Y then" and "if not (X or Y) then" are. The @code{then} keyword is optional as shown The @code{#} must be the first non-blank character on a line, but otherwise the format is free form. Spaces or tabs may appear between the @code{#} and the keyword. The keywords and the symbols are case insensitive as in normal Ada code. Comments may be used on a preprocessor line, but other than that, no other tokens may appear on a preprocessor line. Any number of @code{elsif} clauses can be present, including none at all. The @code{else} is optional, as in Ada. The @code{#} marking the start of a preprocessor line must be the first non-blank character on the line, i.e., it must be preceded only by spaces or horizontal tabs. Symbol substitution outside of preprocessor lines is obtained by using the sequence @smallexample $symbol @end smallexample @noindent anywhere within a source line, except in a comment or within a string literal. The identifier following the @code{$} must match one of the symbols defined in the symbol definition file, and the result is to substitute the value of the symbol in place of @code{$symbol} in the output file. Note that although the substitution of strings within a string literal is not possible, it is possible to have a symbol whose defined value is a string literal. So instead of setting XYZ to @code{hello} and writing: @smallexample Header : String := "$XYZ"; @end smallexample @noindent you should set XYZ to @code{"hello"} and write: @smallexample Header : String := $XYZ; @end smallexample @noindent and then the substitution will occur as desired. @node The GNAT Library Browser gnatls @chapter The GNAT Library Browser @code{gnatls} @findex gnatls @cindex Library browser @noindent @code{gnatls} is a tool that outputs information about compiled units. It gives the relationship between objects, unit names and source files. It can also be used to check the source dependencies of a unit as well as various characteristics. Note: to invoke @code{gnatls} with a project file, use the @code{gnat} driver (see @ref{The GNAT Driver and Project Files}). @menu * Running gnatls:: * Switches for gnatls:: * Examples of gnatls Usage:: @end menu @node Running gnatls @section Running @code{gnatls} @noindent The @code{gnatls} command has the form @smallexample $ gnatls switches @var{object_or_ali_file} @end smallexample @noindent The main argument is the list of object or @file{ali} files (@pxref{The Ada Library Information Files}) for which information is requested. In normal mode, without additional option, @code{gnatls} produces a four-column listing. Each line represents information for a specific object. The first column gives the full path of the object, the second column gives the name of the principal unit in this object, the third column gives the status of the source and the fourth column gives the full path of the source representing this unit. Here is a simple example of use: @smallexample $ gnatls *.o ^./^[]^demo1.o demo1 DIF demo1.adb ^./^[]^demo2.o demo2 OK demo2.adb ^./^[]^hello.o h1 OK hello.adb ^./^[]^instr-child.o instr.child MOK instr-child.adb ^./^[]^instr.o instr OK instr.adb ^./^[]^tef.o tef DIF tef.adb ^./^[]^text_io_example.o text_io_example OK text_io_example.adb ^./^[]^tgef.o tgef DIF tgef.adb @end smallexample @noindent The first line can be interpreted as follows: the main unit which is contained in object file @file{demo1.o} is demo1, whose main source is in @file{demo1.adb}. Furthermore, the version of the source used for the compilation of demo1 has been modified (DIF). Each source file has a status qualifier which can be: @table @code @item OK (unchanged) The version of the source file used for the compilation of the specified unit corresponds exactly to the actual source file. @item MOK (slightly modified) The version of the source file used for the compilation of the specified unit differs from the actual source file but not enough to require recompilation. If you use gnatmake with the qualifier @option{^-m (minimal recompilation)^/MINIMAL_RECOMPILATION^}, a file marked MOK will not be recompiled. @item DIF (modified) No version of the source found on the path corresponds to the source used to build this object. @item ??? (file not found) No source file was found for this unit. @item HID (hidden, unchanged version not first on PATH) The version of the source that corresponds exactly to the source used for compilation has been found on the path but it is hidden by another version of the same source that has been modified. @end table @node Switches for gnatls @section Switches for @code{gnatls} @noindent @code{gnatls} recognizes the following switches: @table @option @c !sort! @cindex @option{--version} @command{gnatls} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatls} If @option{--version} was not used, display usage, then exit disregarding all other options. @item ^-a^/ALL_UNITS^ @cindex @option{^-a^/ALL_UNITS^} (@code{gnatls}) Consider all units, including those of the predefined Ada library. Especially useful with @option{^-d^/DEPENDENCIES^}. @item ^-d^/DEPENDENCIES^ @cindex @option{^-d^/DEPENDENCIES^} (@code{gnatls}) List sources from which specified units depend on. @item ^-h^/OUTPUT=OPTIONS^ @cindex @option{^-h^/OUTPUT=OPTIONS^} (@code{gnatls}) Output the list of options. @item ^-o^/OUTPUT=OBJECTS^ @cindex @option{^-o^/OUTPUT=OBJECTS^} (@code{gnatls}) Only output information about object files. @item ^-s^/OUTPUT=SOURCES^ @cindex @option{^-s^/OUTPUT=SOURCES^} (@code{gnatls}) Only output information about source files. @item ^-u^/OUTPUT=UNITS^ @cindex @option{^-u^/OUTPUT=UNITS^} (@code{gnatls}) Only output information about compilation units. @item ^-files^/FILES^=@var{file} @cindex @option{^-files^/FILES^} (@code{gnatls}) Take as arguments the files listed in text file @var{file}. Text file @var{file} may contain empty lines that are ignored. Each nonempty line should contain the name of an existing file. Several such switches may be specified simultaneously. @item ^-aO^/OBJECT_SEARCH=^@var{dir} @itemx ^-aI^/SOURCE_SEARCH=^@var{dir} @itemx ^-I^/SEARCH=^@var{dir} @itemx ^-I-^/NOCURRENT_DIRECTORY^ @itemx -nostdinc @cindex @option{^-aO^/OBJECT_SEARCH^} (@code{gnatls}) @cindex @option{^-aI^/SOURCE_SEARCH^} (@code{gnatls}) @cindex @option{^-I^/SEARCH^} (@code{gnatls}) @cindex @option{^-I-^/NOCURRENT_DIRECTORY^} (@code{gnatls}) Source path manipulation. Same meaning as the equivalent @command{gnatmake} flags (@pxref{Switches for gnatmake}). @item --RTS=@var{rts-path} @cindex @option{--RTS} (@code{gnatls}) Specifies the default location of the runtime library. Same meaning as the equivalent @command{gnatmake} flag (@pxref{Switches for gnatmake}). @item ^-v^/OUTPUT=VERBOSE^ @cindex @option{^-v^/OUTPUT=VERBOSE^} (@code{gnatls}) Verbose mode. Output the complete source, object and project paths. Do not use the default column layout but instead use long format giving as much as information possible on each requested units, including special characteristics such as: @table @code @item Preelaborable The unit is preelaborable in the Ada sense. @item No_Elab_Code No elaboration code has been produced by the compiler for this unit. @item Pure The unit is pure in the Ada sense. @item Elaborate_Body The unit contains a pragma Elaborate_Body. @item Remote_Types The unit contains a pragma Remote_Types. @item Shared_Passive The unit contains a pragma Shared_Passive. @item Predefined This unit is part of the predefined environment and cannot be modified by the user. @item Remote_Call_Interface The unit contains a pragma Remote_Call_Interface. @end table @end table @node Examples of gnatls Usage @section Example of @code{gnatls} Usage @ifclear vms @noindent Example of using the verbose switch. Note how the source and object paths are affected by the -I switch. @smallexample $ gnatls -v -I.. demo1.o GNATLS 5.03w (20041123-34) Copyright 1997-2004 Free Software Foundation, Inc. Source Search Path: ../ /home/comar/local/adainclude/ Object Search Path: ../ /home/comar/local/lib/gcc-lib/x86-linux/3.4.3/adalib/ Project Search Path: /home/comar/local/lib/gnat/ ./demo1.o Unit => Name => demo1 Kind => subprogram body Flags => No_Elab_Code Source => demo1.adb modified @end smallexample @noindent The following is an example of use of the dependency list. Note the use of the -s switch which gives a straight list of source files. This can be useful for building specialized scripts. @smallexample $ gnatls -d demo2.o ./demo2.o demo2 OK demo2.adb OK gen_list.ads OK gen_list.adb OK instr.ads OK instr-child.ads $ gnatls -d -s -a demo1.o demo1.adb /home/comar/local/adainclude/ada.ads /home/comar/local/adainclude/a-finali.ads /home/comar/local/adainclude/a-filico.ads /home/comar/local/adainclude/a-stream.ads /home/comar/local/adainclude/a-tags.ads gen_list.ads gen_list.adb /home/comar/local/adainclude/gnat.ads /home/comar/local/adainclude/g-io.ads instr.ads /home/comar/local/adainclude/system.ads /home/comar/local/adainclude/s-exctab.ads /home/comar/local/adainclude/s-finimp.ads /home/comar/local/adainclude/s-finroo.ads /home/comar/local/adainclude/s-secsta.ads /home/comar/local/adainclude/s-stalib.ads /home/comar/local/adainclude/s-stoele.ads /home/comar/local/adainclude/s-stratt.ads /home/comar/local/adainclude/s-tasoli.ads /home/comar/local/adainclude/s-unstyp.ads /home/comar/local/adainclude/unchconv.ads @end smallexample @end ifclear @ifset vms @smallexample GNAT LIST /DEPENDENCIES /OUTPUT=SOURCES /ALL_UNITS DEMO1.ADB GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]ada.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]a-finali.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]a-filico.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]a-stream.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]a-tags.ads demo1.adb gen_list.ads gen_list.adb GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]gnat.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]g-io.ads instr.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]system.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-exctab.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-finimp.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-finroo.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-secsta.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-stalib.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-stoele.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-stratt.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-tasoli.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]s-unstyp.ads GNU:[LIB.OPENVMS7_1.2_8_1.ADALIB]unchconv.ads @end smallexample @end ifset @node Cleaning Up Using gnatclean @chapter Cleaning Up Using @code{gnatclean} @findex gnatclean @cindex Cleaning tool @noindent @code{gnatclean} is a tool that allows the deletion of files produced by the compiler, binder and linker, including ALI files, object files, tree files, expanded source files, library files, interface copy source files, binder generated files and executable files. @menu * Running gnatclean:: * Switches for gnatclean:: @c * Examples of gnatclean Usage:: @end menu @node Running gnatclean @section Running @code{gnatclean} @noindent The @code{gnatclean} command has the form: @smallexample $ gnatclean switches @var{names} @end smallexample @noindent @var{names} is a list of source file names. Suffixes @code{.^ads^ADS^} and @code{^adb^ADB^} may be omitted. If a project file is specified using switch @code{^-P^/PROJECT_FILE=^}, then @var{names} may be completely omitted. @noindent In normal mode, @code{gnatclean} delete the files produced by the compiler and, if switch @code{^-c^/COMPILER_FILES_ONLY^} is not specified, by the binder and the linker. In informative-only mode, specified by switch @code{^-n^/NODELETE^}, the list of files that would have been deleted in normal mode is listed, but no file is actually deleted. @node Switches for gnatclean @section Switches for @code{gnatclean} @noindent @code{gnatclean} recognizes the following switches: @table @option @c !sort! @cindex @option{--version} @command{gnatclean} Display Copyright and version, then exit disregarding all other options. @item --help @cindex @option{--help} @command{gnatclean} If @option{--version} was not used, display usage, then exit disregarding all other options. @item ^--subdirs^/SUBDIRS^=subdir Actual object directory of each project file is the subdirectory subdir of the object directory specified or defauted in the project file. @item ^--unchecked-shared-lib-imports^/UNCHECKED_SHARED_LIB_IMPORTS^ By default, shared library projects are not allowed to import static library projects. When this switch is used on the command line, this restriction is relaxed. @item ^-c^/COMPILER_FILES_ONLY^ @cindex @option{^-c^/COMPILER_FILES_ONLY^} (@code{gnatclean}) Only attempt to delete the files produced by the compiler, not those produced by the binder or the linker. The files that are not to be deleted are library files, interface copy files, binder generated files and executable files. @item ^-D ^/DIRECTORY_OBJECTS=^@var{dir} @cindex @option{^-D^/DIRECTORY_OBJECTS^} (@code{gnatclean}) Indicate that ALI and object files should normally be found in directory @var{dir}. @item ^-F^/FULL_PATH_IN_BRIEF_MESSAGES^ @cindex @option{^-F^/FULL_PATH_IN_BRIEF_MESSAGES^} (@code{gnatclean}) When using project files, if some errors or warnings are detected during parsing and verbose mode is not in effect (no use of switch ^-v^/VERBOSE^), then error lines start with the full path name of the project file, rather than its simple file name. @item ^-h^/HELP^ @cindex @option{^-h^/HELP^} (@code{gnatclean}) Output a message explaining the usage of @code{^gnatclean^gnatclean^}. @item ^-n^/NODELETE^ @cindex @option{^-n^/NODELETE^} (@code{gnatclean}) Informative-only mode. Do not delete any files. Output the list of the files that would have been deleted if this switch was not specified. @item ^-P^/PROJECT_FILE=^@var{project} @cindex @option{^-P^/PROJECT_FILE^} (@code{gnatclean}) Use project file @var{project}. Only one such switch can be used. When cleaning a project file, the files produced by the compilation of the immediate sources or inherited sources of the project files are to be deleted. This is not depending on the presence or not of executable names on the command line. @item ^-q^/QUIET^ @cindex @option{^-q^/QUIET^} (@code{gnatclean}) Quiet output. If there are no errors, do not output anything, except in verbose mode (switch ^-v^/VERBOSE^) or in informative-only mode (switch ^-n^/NODELETE^). @item ^-r^/RECURSIVE^ @cindex @option{^-r^/RECURSIVE^} (@code{gnatclean}) When a project file is specified (using switch ^-P^/PROJECT_FILE=^), clean all imported and extended project files, recursively. If this switch is not specified, only the files related to the main project file are to be deleted. This switch has no effect if no project file is specified. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@code{gnatclean}) Verbose mode. @item ^-vP^/MESSAGES_PROJECT_FILE=^@emph{x} @cindex @option{^-vP^/MESSAGES_PROJECT_FILE^} (@code{gnatclean}) Indicates the verbosity of the parsing of GNAT project files. @xref{Switches Related to Project Files}. @item ^-X^/EXTERNAL_REFERENCE=^@var{name=value} @cindex @option{^-X^/EXTERNAL_REFERENCE^} (@code{gnatclean}) Indicates that external variable @var{name} has the value @var{value}. The Project Manager will use this value for occurrences of @code{external(name)} when parsing the project file. @xref{Switches Related to Project Files}. @item ^-aO^/OBJECT_SEARCH=^@var{dir} @cindex @option{^-aO^/OBJECT_SEARCH^} (@code{gnatclean}) When searching for ALI and object files, look in directory @var{dir}. @item ^-I^/SEARCH=^@var{dir} @cindex @option{^-I^/SEARCH^} (@code{gnatclean}) Equivalent to @option{^-aO^/OBJECT_SEARCH=^@var{dir}}. @item ^-I-^/NOCURRENT_DIRECTORY^ @cindex @option{^-I-^/NOCURRENT_DIRECTORY^} (@code{gnatclean}) @cindex Source files, suppressing search Do not look for ALI or object files in the directory where @code{gnatclean} was invoked. @end table @c @node Examples of gnatclean Usage @c @section Examples of @code{gnatclean} Usage @ifclear vms @node GNAT and Libraries @chapter GNAT and Libraries @cindex Library, building, installing, using @noindent This chapter describes how to build and use libraries with GNAT, and also shows how to recompile the GNAT run-time library. You should be familiar with the Project Manager facility (@pxref{GNAT Project Manager}) before reading this chapter. @menu * Introduction to Libraries in GNAT:: * General Ada Libraries:: * Stand-alone Ada Libraries:: * Rebuilding the GNAT Run-Time Library:: @end menu @node Introduction to Libraries in GNAT @section Introduction to Libraries in GNAT @noindent A library is, conceptually, a collection of objects which does not have its own main thread of execution, but rather provides certain services to the applications that use it. A library can be either statically linked with the application, in which case its code is directly included in the application, or, on platforms that support it, be dynamically linked, in which case its code is shared by all applications making use of this library. GNAT supports both types of libraries. In the static case, the compiled code can be provided in different ways. The simplest approach is to provide directly the set of objects resulting from compilation of the library source files. Alternatively, you can group the objects into an archive using whatever commands are provided by the operating system. For the latter case, the objects are grouped into a shared library. In the GNAT environment, a library has three types of components: @itemize @bullet @item Source files. @item @file{ALI} files. @xref{The Ada Library Information Files}. @item Object files, an archive or a shared library. @end itemize @noindent A GNAT library may expose all its source files, which is useful for documentation purposes. Alternatively, it may expose only the units needed by an external user to make use of the library. That is to say, the specs reflecting the library services along with all the units needed to compile those specs, which can include generic bodies or any body implementing an inlined routine. In the case of @emph{stand-alone libraries} those exposed units are called @emph{interface units} (@pxref{Stand-alone Ada Libraries}). All compilation units comprising an application, including those in a library, need to be elaborated in an order partially defined by Ada's semantics. GNAT computes the elaboration order from the @file{ALI} files and this is why they constitute a mandatory part of GNAT libraries. @emph{Stand-alone libraries} are the exception to this rule because a specific library elaboration routine is produced independently of the application(s) using the library. @node General Ada Libraries @section General Ada Libraries @menu * Building a library:: * Installing a library:: * Using a library:: @end menu @node Building a library @subsection Building a library @noindent The easiest way to build a library is to use the Project Manager, which supports a special type of project called a @emph{Library Project} (@pxref{Library Projects}). A project is considered a library project, when two project-level attributes are defined in it: @code{Library_Name} and @code{Library_Dir}. In order to control different aspects of library configuration, additional optional project-level attributes can be specified: @table @code @item Library_Kind This attribute controls whether the library is to be static or dynamic @item Library_Version This attribute specifies the library version; this value is used during dynamic linking of shared libraries to determine if the currently installed versions of the binaries are compatible. @item Library_Options @item Library_GCC These attributes specify additional low-level options to be used during library generation, and redefine the actual application used to generate library. @end table @noindent The GNAT Project Manager takes full care of the library maintenance task, including recompilation of the source files for which objects do not exist or are not up to date, assembly of the library archive, and installation of the library (i.e., copying associated source, object and @file{ALI} files to the specified location). Here is a simple library project file: @smallexample @c ada project My_Lib is for Source_Dirs use ("src1", "src2"); for Object_Dir use "obj"; for Library_Name use "mylib"; for Library_Dir use "lib"; for Library_Kind use "dynamic"; end My_lib; @end smallexample @noindent and the compilation command to build and install the library: @smallexample @c ada $ gnatmake -Pmy_lib @end smallexample @noindent It is not entirely trivial to perform manually all the steps required to produce a library. We recommend that you use the GNAT Project Manager for this task. In special cases where this is not desired, the necessary steps are discussed below. There are various possibilities for compiling the units that make up the library: for example with a Makefile (@pxref{Using the GNU make Utility}) or with a conventional script. For simple libraries, it is also possible to create a dummy main program which depends upon all the packages that comprise the interface of the library. This dummy main program can then be given to @command{gnatmake}, which will ensure that all necessary objects are built. After this task is accomplished, you should follow the standard procedure of the underlying operating system to produce the static or shared library. Here is an example of such a dummy program: @smallexample @c ada @group with My_Lib.Service1; with My_Lib.Service2; with My_Lib.Service3; procedure My_Lib_Dummy is begin null; end; @end group @end smallexample @noindent Here are the generic commands that will build an archive or a shared library. @smallexample # compiling the library $ gnatmake -c my_lib_dummy.adb # we don't need the dummy object itself $ rm my_lib_dummy.o my_lib_dummy.ali # create an archive with the remaining objects $ ar rc libmy_lib.a *.o # some systems may require "ranlib" to be run as well # or create a shared library $ gcc -shared -o libmy_lib.so *.o # some systems may require the code to have been compiled with -fPIC # remove the object files that are now in the library $ rm *.o # Make the ALI files read-only so that gnatmake will not try to # regenerate the objects that are in the library $ chmod -w *.ali @end smallexample @noindent Please note that the library must have a name of the form @file{lib@var{xxx}.a} or @file{lib@var{xxx}.so} (or @file{lib@var{xxx}.dll} on Windows) in order to be accessed by the directive @option{-l@var{xxx}} at link time. @node Installing a library @subsection Installing a library @cindex @code{ADA_PROJECT_PATH} @cindex @code{GPR_PROJECT_PATH} @noindent If you use project files, library installation is part of the library build process (@pxref{Installing a library with project files}). When project files are not an option, it is also possible, but not recommended, to install the library so that the sources needed to use the library are on the Ada source path and the ALI files & libraries be on the Ada Object path (see @ref{Search Paths and the Run-Time Library (RTL)}. Alternatively, the system administrator can place general-purpose libraries in the default compiler paths, by specifying the libraries' location in the configuration files @file{ada_source_path} and @file{ada_object_path}. These configuration files must be located in the GNAT installation tree at the same place as the gcc spec file. The location of the gcc spec file can be determined as follows: @smallexample $ gcc -v @end smallexample @noindent The configuration files mentioned above have a simple format: each line must contain one unique directory name. Those names are added to the corresponding path in their order of appearance in the file. The names can be either absolute or relative; in the latter case, they are relative to where theses files are located. The files @file{ada_source_path} and @file{ada_object_path} might not be present in a GNAT installation, in which case, GNAT will look for its run-time library in the directories @file{adainclude} (for the sources) and @file{adalib} (for the objects and @file{ALI} files). When the files exist, the compiler does not look in @file{adainclude} and @file{adalib}, and thus the @file{ada_source_path} file must contain the location for the GNAT run-time sources (which can simply be @file{adainclude}). In the same way, the @file{ada_object_path} file must contain the location for the GNAT run-time objects (which can simply be @file{adalib}). You can also specify a new default path to the run-time library at compilation time with the switch @option{--RTS=rts-path}. You can thus choose / change the run-time library you want your program to be compiled with. This switch is recognized by @command{gcc}, @command{gnatmake}, @command{gnatbind}, @command{gnatls}, @command{gnatfind} and @command{gnatxref}. It is possible to install a library before or after the standard GNAT library, by reordering the lines in the configuration files. In general, a library must be installed before the GNAT library if it redefines any part of it. @node Using a library @subsection Using a library @noindent Once again, the project facility greatly simplifies the use of libraries. In this context, using a library is just a matter of adding a @code{with} clause in the user project. For instance, to make use of the library @code{My_Lib} shown in examples in earlier sections, you can write: @smallexample @c projectfile with "my_lib"; project My_Proj is @dots{} end My_Proj; @end smallexample Even if you have a third-party, non-Ada library, you can still use GNAT's Project Manager facility to provide a wrapper for it. For example, the following project, when @code{with}ed by your main project, will link with the third-party library @file{liba.a}: @smallexample @c projectfile @group project Liba is for Externally_Built use "true"; for Source_Files use (); for Library_Dir use "lib"; for Library_Name use "a"; for Library_Kind use "static"; end Liba; @end group @end smallexample This is an alternative to the use of @code{pragma Linker_Options}. It is especially interesting in the context of systems with several interdependent static libraries where finding a proper linker order is not easy and best be left to the tools having visibility over project dependence information. @noindent In order to use an Ada library manually, you need to make sure that this library is on both your source and object path (see @ref{Search Paths and the Run-Time Library (RTL)} and @ref{Search Paths for gnatbind}). Furthermore, when the objects are grouped in an archive or a shared library, you need to specify the desired library at link time. For example, you can use the library @file{mylib} installed in @file{/dir/my_lib_src} and @file{/dir/my_lib_obj} with the following commands: @smallexample $ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \ -largs -lmy_lib @end smallexample @noindent This can be expressed more simply: @smallexample $ gnatmake my_appl @end smallexample @noindent when the following conditions are met: @itemize @bullet @item @file{/dir/my_lib_src} has been added by the user to the environment variable @env{ADA_INCLUDE_PATH}, or by the administrator to the file @file{ada_source_path} @item @file{/dir/my_lib_obj} has been added by the user to the environment variable @env{ADA_OBJECTS_PATH}, or by the administrator to the file @file{ada_object_path} @item a pragma @code{Linker_Options} has been added to one of the sources. For example: @smallexample @c ada pragma Linker_Options ("-lmy_lib"); @end smallexample @end itemize @node Stand-alone Ada Libraries @section Stand-alone Ada Libraries @cindex Stand-alone library, building, using @menu * Introduction to Stand-alone Libraries:: * Building a Stand-alone Library:: * Creating a Stand-alone Library to be used in a non-Ada context:: * Restrictions in Stand-alone Libraries:: @end menu @node Introduction to Stand-alone Libraries @subsection Introduction to Stand-alone Libraries @noindent A Stand-alone Library (abbreviated ``SAL'') is a library that contains the necessary code to elaborate the Ada units that are included in the library. In contrast with an ordinary library, which consists of all sources, objects and @file{ALI} files of the library, a SAL may specify a restricted subset of compilation units to serve as a library interface. In this case, the fully self-sufficient set of files will normally consist of an objects archive, the sources of interface units' specs, and the @file{ALI} files of interface units. If an interface spec contains a generic unit or an inlined subprogram, the body's source must also be provided; if the units that must be provided in the source form depend on other units, the source and @file{ALI} files of those must also be provided. The main purpose of a SAL is to minimize the recompilation overhead of client applications when a new version of the library is installed. Specifically, if the interface sources have not changed, client applications do not need to be recompiled. If, furthermore, a SAL is provided in the shared form and its version, controlled by @code{Library_Version} attribute, is not changed, then the clients do not need to be relinked. SALs also allow the library providers to minimize the amount of library source text exposed to the clients. Such ``information hiding'' might be useful or necessary for various reasons. Stand-alone libraries are also well suited to be used in an executable whose main routine is not written in Ada. @node Building a Stand-alone Library @subsection Building a Stand-alone Library @noindent GNAT's Project facility provides a simple way of building and installing stand-alone libraries; see @ref{Stand-alone Library Projects}. To be a Stand-alone Library Project, in addition to the two attributes that make a project a Library Project (@code{Library_Name} and @code{Library_Dir}; see @ref{Library Projects}), the attribute @code{Library_Interface} must be defined. For example: @smallexample @c projectfile @group for Library_Dir use "lib_dir"; for Library_Name use "dummy"; for Library_Interface use ("int1", "int1.child"); @end group @end smallexample @noindent Attribute @code{Library_Interface} has a non-empty string list value, each string in the list designating a unit contained in an immediate source of the project file. When a Stand-alone Library is built, first the binder is invoked to build a package whose name depends on the library name (@file{^b~dummy.ads/b^B$DUMMY.ADS/B^} in the example above). This binder-generated package includes initialization and finalization procedures whose names depend on the library name (@code{dummyinit} and @code{dummyfinal} in the example above). The object corresponding to this package is included in the library. You must ensure timely (e.g., prior to any use of interfaces in the SAL) calling of these procedures if a static SAL is built, or if a shared SAL is built with the project-level attribute @code{Library_Auto_Init} set to @code{"false"}. For a Stand-Alone Library, only the @file{ALI} files of the Interface Units (those that are listed in attribute @code{Library_Interface}) are copied to the Library Directory. As a consequence, only the Interface Units may be imported from Ada units outside of the library. If other units are imported, the binding phase will fail. The attribute @code{Library_Src_Dir} may be specified for a Stand-Alone Library. @code{Library_Src_Dir} is a simple attribute that has a single string value. Its value must be the path (absolute or relative to the project directory) of an existing directory. This directory cannot be the object directory or one of the source directories, but it can be the same as the library directory. The sources of the Interface Units of the library that are needed by an Ada client of the library will be copied to the designated directory, called the Interface Copy directory. These sources include the specs of the Interface Units, but they may also include bodies and subunits, when pragmas @code{Inline} or @code{Inline_Always} are used, or when there is a generic unit in the spec. Before the sources are copied to the Interface Copy directory, an attempt is made to delete all files in the Interface Copy directory. Building stand-alone libraries by hand is somewhat tedious, but for those occasions when it is necessary here are the steps that you need to perform: @itemize @bullet @item Compile all library sources. @item Invoke the binder with the switch @option{-n} (No Ada main program), with all the @file{ALI} files of the interfaces, and with the switch @option{-L} to give specific names to the @code{init} and @code{final} procedures. For example: @smallexample gnatbind -n int1.ali int2.ali -Lsal1 @end smallexample @item Compile the binder generated file: @smallexample gcc -c b~int2.adb @end smallexample @item Link the dynamic library with all the necessary object files, indicating to the linker the names of the @code{init} (and possibly @code{final}) procedures for automatic initialization (and finalization). The built library should be placed in a directory different from the object directory. @item Copy the @code{ALI} files of the interface to the library directory, add in this copy an indication that it is an interface to a SAL (i.e., add a word @option{SL} on the line in the @file{ALI} file that starts with letter ``P'') and make the modified copy of the @file{ALI} file read-only. @end itemize @noindent Using SALs is not different from using other libraries (see @ref{Using a library}). @node Creating a Stand-alone Library to be used in a non-Ada context @subsection Creating a Stand-alone Library to be used in a non-Ada context @noindent It is easy to adapt the SAL build procedure discussed above for use of a SAL in a non-Ada context. The only extra step required is to ensure that library interface subprograms are compatible with the main program, by means of @code{pragma Export} or @code{pragma Convention}. Here is an example of simple library interface for use with C main program: @smallexample @c ada package My_Package is procedure Do_Something; pragma Export (C, Do_Something, "do_something"); procedure Do_Something_Else; pragma Export (C, Do_Something_Else, "do_something_else"); end My_Package; @end smallexample @noindent On the foreign language side, you must provide a ``foreign'' view of the library interface; remember that it should contain elaboration routines in addition to interface subprograms. The example below shows the content of @code{mylib_interface.h} (note that there is no rule for the naming of this file, any name can be used) @smallexample /* the library elaboration procedure */ extern void mylibinit (void); /* the library finalization procedure */ extern void mylibfinal (void); /* the interface exported by the library */ extern void do_something (void); extern void do_something_else (void); @end smallexample @noindent Libraries built as explained above can be used from any program, provided that the elaboration procedures (named @code{mylibinit} in the previous example) are called before the library services are used. Any number of libraries can be used simultaneously, as long as the elaboration procedure of each library is called. Below is an example of a C program that uses the @code{mylib} library. @smallexample #include "mylib_interface.h" int main (void) @{ /* First, elaborate the library before using it */ mylibinit (); /* Main program, using the library exported entities */ do_something (); do_something_else (); /* Library finalization at the end of the program */ mylibfinal (); return 0; @} @end smallexample @noindent Note that invoking any library finalization procedure generated by @code{gnatbind} shuts down the Ada run-time environment. Consequently, the finalization of all Ada libraries must be performed at the end of the program. No call to these libraries or to the Ada run-time library should be made after the finalization phase. @node Restrictions in Stand-alone Libraries @subsection Restrictions in Stand-alone Libraries @noindent The pragmas listed below should be used with caution inside libraries, as they can create incompatibilities with other Ada libraries: @itemize @bullet @item pragma @code{Locking_Policy} @item pragma @code{Queuing_Policy} @item pragma @code{Task_Dispatching_Policy} @item pragma @code{Unreserve_All_Interrupts} @end itemize @noindent When using a library that contains such pragmas, the user must make sure that all libraries use the same pragmas with the same values. Otherwise, @code{Program_Error} will be raised during the elaboration of the conflicting libraries. The usage of these pragmas and its consequences for the user should therefore be well documented. Similarly, the traceback in the exception occurrence mechanism should be enabled or disabled in a consistent manner across all libraries. Otherwise, Program_Error will be raised during the elaboration of the conflicting libraries. If the @code{Version} or @code{Body_Version} attributes are used inside a library, then you need to perform a @code{gnatbind} step that specifies all @file{ALI} files in all libraries, so that version identifiers can be properly computed. In practice these attributes are rarely used, so this is unlikely to be a consideration. @node Rebuilding the GNAT Run-Time Library @section Rebuilding the GNAT Run-Time Library @cindex GNAT Run-Time Library, rebuilding @cindex Building the GNAT Run-Time Library @cindex Rebuilding the GNAT Run-Time Library @cindex Run-Time Library, rebuilding @noindent It may be useful to recompile the GNAT library in various contexts, the most important one being the use of partition-wide configuration pragmas such as @code{Normalize_Scalars}. A special Makefile called @code{Makefile.adalib} is provided to that effect and can be found in the directory containing the GNAT library. The location of this directory depends on the way the GNAT environment has been installed and can be determined by means of the command: @smallexample $ gnatls -v @end smallexample @noindent The last entry in the object search path usually contains the gnat library. This Makefile contains its own documentation and in particular the set of instructions needed to rebuild a new library and to use it. @node Using the GNU make Utility @chapter Using the GNU @code{make} Utility @findex make @noindent This chapter offers some examples of makefiles that solve specific problems. It does not explain how to write a makefile (@pxref{Top,, GNU make, make, GNU @code{make}}), nor does it try to replace the @command{gnatmake} utility (@pxref{The GNAT Make Program gnatmake}). All the examples in this section are specific to the GNU version of make. Although @command{make} is a standard utility, and the basic language is the same, these examples use some advanced features found only in @code{GNU make}. @menu * Using gnatmake in a Makefile:: * Automatically Creating a List of Directories:: * Generating the Command Line Switches:: * Overcoming Command Line Length Limits:: @end menu @node Using gnatmake in a Makefile @section Using gnatmake in a Makefile @findex makefile @cindex GNU make @noindent Complex project organizations can be handled in a very powerful way by using GNU make combined with gnatmake. For instance, here is a Makefile which allows you to build each subsystem of a big project into a separate shared library. Such a makefile allows you to significantly reduce the link time of very big applications while maintaining full coherence at each step of the build process. The list of dependencies are handled automatically by @command{gnatmake}. The Makefile is simply used to call gnatmake in each of the appropriate directories. Note that you should also read the example on how to automatically create the list of directories (@pxref{Automatically Creating a List of Directories}) which might help you in case your project has a lot of subdirectories. @smallexample @iftex @leftskip=0cm @font@heightrm=cmr8 @heightrm @end iftex ## This Makefile is intended to be used with the following directory ## configuration: ## - The sources are split into a series of csc (computer software components) ## Each of these csc is put in its own directory. ## Their name are referenced by the directory names. ## They will be compiled into shared library (although this would also work ## with static libraries ## - The main program (and possibly other packages that do not belong to any ## csc is put in the top level directory (where the Makefile is). ## toplevel_dir __ first_csc (sources) __ lib (will contain the library) ## \_ second_csc (sources) __ lib (will contain the library) ## \_ @dots{} ## Although this Makefile is build for shared library, it is easy to modify ## to build partial link objects instead (modify the lines with -shared and ## gnatlink below) ## ## With this makefile, you can change any file in the system or add any new ## file, and everything will be recompiled correctly (only the relevant shared ## objects will be recompiled, and the main program will be re-linked). # The list of computer software component for your project. This might be # generated automatically. CSC_LIST=aa bb cc # Name of the main program (no extension) MAIN=main # If we need to build objects with -fPIC, uncomment the following line #NEED_FPIC=-fPIC # The following variable should give the directory containing libgnat.so # You can get this directory through 'gnatls -v'. This is usually the last # directory in the Object_Path. GLIB=@dots{} # The directories for the libraries # (This macro expands the list of CSC to the list of shared libraries, you # could simply use the expanded form: # LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so LIB_DIR=$@{foreach dir,$@{CSC_LIST@},$@{dir@}/lib/lib$@{dir@}.so@} $@{MAIN@}: objects $@{LIB_DIR@} gnatbind $@{MAIN@} $@{CSC_LIST:%=-aO%/lib@} -shared gnatlink $@{MAIN@} $@{CSC_LIST:%=-l%@} objects:: # recompile the sources gnatmake -c -i $@{MAIN@}.adb $@{NEED_FPIC@} $@{CSC_LIST:%=-I%@} # Note: In a future version of GNAT, the following commands will be simplified # by a new tool, gnatmlib $@{LIB_DIR@}: mkdir -p $@{dir $@@ @} cd $@{dir $@@ @} && gcc -shared -o $@{notdir $@@ @} ../*.o -L$@{GLIB@} -lgnat cd $@{dir $@@ @} && cp -f ../*.ali . # The dependencies for the modules # Note that we have to force the expansion of *.o, since in some cases # make won't be able to do it itself. aa/lib/libaa.so: $@{wildcard aa/*.o@} bb/lib/libbb.so: $@{wildcard bb/*.o@} cc/lib/libcc.so: $@{wildcard cc/*.o@} # Make sure all of the shared libraries are in the path before starting the # program run:: LD_LIBRARY_PATH=`pwd`/aa/lib:`pwd`/bb/lib:`pwd`/cc/lib ./$@{MAIN@} clean:: $@{RM@} -rf $@{CSC_LIST:%=%/lib@} $@{RM@} $@{CSC_LIST:%=%/*.ali@} $@{RM@} $@{CSC_LIST:%=%/*.o@} $@{RM@} *.o *.ali $@{MAIN@} @end smallexample @node Automatically Creating a List of Directories @section Automatically Creating a List of Directories @noindent In most makefiles, you will have to specify a list of directories, and store it in a variable. For small projects, it is often easier to specify each of them by hand, since you then have full control over what is the proper order for these directories, which ones should be included. However, in larger projects, which might involve hundreds of subdirectories, it might be more convenient to generate this list automatically. The example below presents two methods. The first one, although less general, gives you more control over the list. It involves wildcard characters, that are automatically expanded by @command{make}. Its shortcoming is that you need to explicitly specify some of the organization of your project, such as for instance the directory tree depth, whether some directories are found in a separate tree, @enddots{} The second method is the most general one. It requires an external program, called @command{find}, which is standard on all Unix systems. All the directories found under a given root directory will be added to the list. @smallexample @iftex @leftskip=0cm @font@heightrm=cmr8 @heightrm @end iftex # The examples below are based on the following directory hierarchy: # All the directories can contain any number of files # ROOT_DIRECTORY -> a -> aa -> aaa # -> ab # -> ac # -> b -> ba -> baa # -> bb # -> bc # This Makefile creates a variable called DIRS, that can be reused any time # you need this list (see the other examples in this section) # The root of your project's directory hierarchy ROOT_DIRECTORY=. #### # First method: specify explicitly the list of directories # This allows you to specify any subset of all the directories you need. #### DIRS := a/aa/ a/ab/ b/ba/ #### # Second method: use wildcards # Note that the argument(s) to wildcard below should end with a '/'. # Since wildcards also return file names, we have to filter them out # to avoid duplicate directory names. # We thus use make's @code{dir} and @code{sort} functions. # It sets DIRs to the following value (note that the directories aaa and baa # are not given, unless you change the arguments to wildcard). # DIRS= ./a/a/ ./b/ ./a/aa/ ./a/ab/ ./a/ac/ ./b/ba/ ./b/bb/ ./b/bc/ #### DIRS := $@{sort $@{dir $@{wildcard $@{ROOT_DIRECTORY@}/*/ $@{ROOT_DIRECTORY@}/*/*/@}@}@} #### # Third method: use an external program # This command is much faster if run on local disks, avoiding NFS slowdowns. # This is the most complete command: it sets DIRs to the following value: # DIRS= ./a ./a/aa ./a/aa/aaa ./a/ab ./a/ac ./b ./b/ba ./b/ba/baa ./b/bb ./b/bc #### DIRS := $@{shell find $@{ROOT_DIRECTORY@} -type d -print@} @end smallexample @node Generating the Command Line Switches @section Generating the Command Line Switches @noindent Once you have created the list of directories as explained in the previous section (@pxref{Automatically Creating a List of Directories}), you can easily generate the command line arguments to pass to gnatmake. For the sake of completeness, this example assumes that the source path is not the same as the object path, and that you have two separate lists of directories. @smallexample # see "Automatically creating a list of directories" to create # these variables SOURCE_DIRS= OBJECT_DIRS= GNATMAKE_SWITCHES := $@{patsubst %,-aI%,$@{SOURCE_DIRS@}@} GNATMAKE_SWITCHES += $@{patsubst %,-aO%,$@{OBJECT_DIRS@}@} all: gnatmake $@{GNATMAKE_SWITCHES@} main_unit @end smallexample @node Overcoming Command Line Length Limits @section Overcoming Command Line Length Limits @noindent One problem that might be encountered on big projects is that many operating systems limit the length of the command line. It is thus hard to give gnatmake the list of source and object directories. This example shows how you can set up environment variables, which will make @command{gnatmake} behave exactly as if the directories had been specified on the command line, but have a much higher length limit (or even none on most systems). It assumes that you have created a list of directories in your Makefile, using one of the methods presented in @ref{Automatically Creating a List of Directories}. For the sake of completeness, we assume that the object path (where the ALI files are found) is different from the sources patch. Note a small trick in the Makefile below: for efficiency reasons, we create two temporary variables (SOURCE_LIST and OBJECT_LIST), that are expanded immediately by @code{make}. This way we overcome the standard make behavior which is to expand the variables only when they are actually used. On Windows, if you are using the standard Windows command shell, you must replace colons with semicolons in the assignments to these variables. @smallexample @iftex @leftskip=0cm @font@heightrm=cmr8 @heightrm @end iftex # In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECT_PATH. # This is the same thing as putting the -I arguments on the command line. # (the equivalent of using -aI on the command line would be to define # only ADA_INCLUDE_PATH, the equivalent of -aO is ADA_OBJECT_PATH). # You can of course have different values for these variables. # # Note also that we need to keep the previous values of these variables, since # they might have been set before running 'make' to specify where the GNAT # library is installed. # see "Automatically creating a list of directories" to create these # variables SOURCE_DIRS= OBJECT_DIRS= empty:= space:=$@{empty@} $@{empty@} SOURCE_LIST := $@{subst $@{space@},:,$@{SOURCE_DIRS@}@} OBJECT_LIST := $@{subst $@{space@},:,$@{OBJECT_DIRS@}@} ADA_INCLUDE_PATH += $@{SOURCE_LIST@} ADA_OBJECT_PATH += $@{OBJECT_LIST@} export ADA_INCLUDE_PATH export ADA_OBJECT_PATH all: gnatmake main_unit @end smallexample @end ifclear @node Memory Management Issues @chapter Memory Management Issues @noindent This chapter describes some useful memory pools provided in the GNAT library and in particular the GNAT Debug Pool facility, which can be used to detect incorrect uses of access values (including ``dangling references''). @ifclear vms It also describes the @command{gnatmem} tool, which can be used to track down ``memory leaks''. @end ifclear @menu * Some Useful Memory Pools:: * The GNAT Debug Pool Facility:: @ifclear vms * The gnatmem Tool:: @end ifclear @end menu @node Some Useful Memory Pools @section Some Useful Memory Pools @findex Memory Pool @cindex storage, pool @noindent The @code{System.Pool_Global} package offers the Unbounded_No_Reclaim_Pool storage pool. Allocations use the standard system call @code{malloc} while deallocations use the standard system call @code{free}. No reclamation is performed when the pool goes out of scope. For performance reasons, the standard default Ada allocators/deallocators do not use any explicit storage pools but if they did, they could use this storage pool without any change in behavior. That is why this storage pool is used when the user manages to make the default implicit allocator explicit as in this example: @smallexample @c ada type T1 is access Something; -- no Storage pool is defined for T2 type T2 is access Something_Else; for T2'Storage_Pool use T1'Storage_Pool; -- the above is equivalent to for T2'Storage_Pool use System.Pool_Global.Global_Pool_Object; @end smallexample @noindent The @code{System.Pool_Local} package offers the Unbounded_Reclaim_Pool storage pool. The allocation strategy is similar to @code{Pool_Local}'s except that the all storage allocated with this pool is reclaimed when the pool object goes out of scope. This pool provides a explicit mechanism similar to the implicit one provided by several Ada 83 compilers for allocations performed through a local access type and whose purpose was to reclaim memory when exiting the scope of a given local access. As an example, the following program does not leak memory even though it does not perform explicit deallocation: @smallexample @c ada with System.Pool_Local; procedure Pooloc1 is procedure Internal is type A is access Integer; X : System.Pool_Local.Unbounded_Reclaim_Pool; for A'Storage_Pool use X; v : A; begin for I in 1 .. 50 loop v := new Integer; end loop; end Internal; begin for I in 1 .. 100 loop Internal; end loop; end Pooloc1; @end smallexample @noindent The @code{System.Pool_Size} package implements the Stack_Bounded_Pool used when @code{Storage_Size} is specified for an access type. The whole storage for the pool is allocated at once, usually on the stack at the point where the access type is elaborated. It is automatically reclaimed when exiting the scope where the access type is defined. This package is not intended to be used directly by the user and it is implicitly used for each such declaration: @smallexample @c ada type T1 is access Something; for T1'Storage_Size use 10_000; @end smallexample @node The GNAT Debug Pool Facility @section The GNAT Debug Pool Facility @findex Debug Pool @cindex storage, pool, memory corruption @noindent The use of unchecked deallocation and unchecked conversion can easily lead to incorrect memory references. The problems generated by such references are usually difficult to tackle because the symptoms can be very remote from the origin of the problem. In such cases, it is very helpful to detect the problem as early as possible. This is the purpose of the Storage Pool provided by @code{GNAT.Debug_Pools}. In order to use the GNAT specific debugging pool, the user must associate a debug pool object with each of the access types that may be related to suspected memory problems. See Ada Reference Manual 13.11. @smallexample @c ada type Ptr is access Some_Type; Pool : GNAT.Debug_Pools.Debug_Pool; for Ptr'Storage_Pool use Pool; @end smallexample @noindent @code{GNAT.Debug_Pools} is derived from a GNAT-specific kind of pool: the @code{Checked_Pool}. Such pools, like standard Ada storage pools, allow the user to redefine allocation and deallocation strategies. They also provide a checkpoint for each dereference, through the use of the primitive operation @code{Dereference} which is implicitly called at each dereference of an access value. Once an access type has been associated with a debug pool, operations on values of the type may raise four distinct exceptions, which correspond to four potential kinds of memory corruption: @itemize @bullet @item @code{GNAT.Debug_Pools.Accessing_Not_Allocated_Storage} @item @code{GNAT.Debug_Pools.Accessing_Deallocated_Storage} @item @code{GNAT.Debug_Pools.Freeing_Not_Allocated_Storage} @item @code{GNAT.Debug_Pools.Freeing_Deallocated_Storage } @end itemize @noindent For types associated with a Debug_Pool, dynamic allocation is performed using the standard GNAT allocation routine. References to all allocated chunks of memory are kept in an internal dictionary. Several deallocation strategies are provided, whereupon the user can choose to release the memory to the system, keep it allocated for further invalid access checks, or fill it with an easily recognizable pattern for debug sessions. The memory pattern is the old IBM hexadecimal convention: @code{16#DEADBEEF#}. See the documentation in the file g-debpoo.ads for more information on the various strategies. Upon each dereference, a check is made that the access value denotes a properly allocated memory location. Here is a complete example of use of @code{Debug_Pools}, that includes typical instances of memory corruption: @smallexample @c ada @iftex @leftskip=0cm @end iftex with Gnat.Io; use Gnat.Io; with Unchecked_Deallocation; with Unchecked_Conversion; with GNAT.Debug_Pools; with System.Storage_Elements; with Ada.Exceptions; use Ada.Exceptions; procedure Debug_Pool_Test is type T is access Integer; type U is access all T; P : GNAT.Debug_Pools.Debug_Pool; for T'Storage_Pool use P; procedure Free is new Unchecked_Deallocation (Integer, T); function UC is new Unchecked_Conversion (U, T); A, B : aliased T; procedure Info is new GNAT.Debug_Pools.Print_Info(Put_Line); begin Info (P); A := new Integer; B := new Integer; B := A; Info (P); Free (A); begin Put_Line (Integer'Image(B.all)); exception when E : others => Put_Line ("raised: " & Exception_Name (E)); end; begin Free (B); exception when E : others => Put_Line ("raised: " & Exception_Name (E)); end; B := UC(A'Access); begin Put_Line (Integer'Image(B.all)); exception when E : others => Put_Line ("raised: " & Exception_Name (E)); end; begin Free (B); exception when E : others => Put_Line ("raised: " & Exception_Name (E)); end; Info (P); end Debug_Pool_Test; @end smallexample @noindent The debug pool mechanism provides the following precise diagnostics on the execution of this erroneous program: @smallexample Debug Pool info: Total allocated bytes : 0 Total deallocated bytes : 0 Current Water Mark: 0 High Water Mark: 0 Debug Pool info: Total allocated bytes : 8 Total deallocated bytes : 0 Current Water Mark: 8 High Water Mark: 8 raised: GNAT.DEBUG_POOLS.ACCESSING_DEALLOCATED_STORAGE raised: GNAT.DEBUG_POOLS.FREEING_DEALLOCATED_STORAGE raised: GNAT.DEBUG_POOLS.ACCESSING_NOT_ALLOCATED_STORAGE raised: GNAT.DEBUG_POOLS.FREEING_NOT_ALLOCATED_STORAGE Debug Pool info: Total allocated bytes : 8 Total deallocated bytes : 4 Current Water Mark: 4 High Water Mark: 8 @end smallexample @ifclear vms @node The gnatmem Tool @section The @command{gnatmem} Tool @findex gnatmem @noindent The @code{gnatmem} utility monitors dynamic allocation and deallocation activity in a program, and displays information about incorrect deallocations and possible sources of memory leaks. It is designed to work in association with a static runtime library only and in this context provides three types of information: @itemize @bullet @item General information concerning memory management, such as the total number of allocations and deallocations, the amount of allocated memory and the high water mark, i.e.@: the largest amount of allocated memory in the course of program execution. @item Backtraces for all incorrect deallocations, that is to say deallocations which do not correspond to a valid allocation. @item Information on each allocation that is potentially the origin of a memory leak. @end itemize @menu * Running gnatmem:: * Switches for gnatmem:: * Example of gnatmem Usage:: @end menu @node Running gnatmem @subsection Running @code{gnatmem} @noindent @code{gnatmem} makes use of the output created by the special version of allocation and deallocation routines that record call information. This allows to obtain accurate dynamic memory usage history at a minimal cost to the execution speed. Note however, that @code{gnatmem} is not supported on all platforms (currently, it is supported on AIX, HP-UX, GNU/Linux, Solaris and Windows NT/2000/XP (x86). @noindent The @code{gnatmem} command has the form @smallexample @c $ gnatmem @ovar{switches} user_program @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatmem @r{[}@var{switches}@r{]} @var{user_program} @end smallexample @noindent The program must have been linked with the instrumented version of the allocation and deallocation routines. This is done by linking with the @file{libgmem.a} library. For correct symbolic backtrace information, the user program should be compiled with debugging options (see @ref{Switches for gcc}). For example to build @file{my_program}: @smallexample $ gnatmake -g my_program -largs -lgmem @end smallexample @noindent As library @file{libgmem.a} contains an alternate body for package @code{System.Memory}, @file{s-memory.adb} should not be compiled and linked when an executable is linked with library @file{libgmem.a}. It is then not recommended to use @command{gnatmake} with switch @option{^-a^/ALL_FILES^}. @noindent When @file{my_program} is executed, the file @file{gmem.out} is produced. This file contains information about all allocations and deallocations performed by the program. It is produced by the instrumented allocations and deallocations routines and will be used by @code{gnatmem}. In order to produce symbolic backtrace information for allocations and deallocations performed by the GNAT run-time library, you need to use a version of that library that has been compiled with the @option{-g} switch (see @ref{Rebuilding the GNAT Run-Time Library}). Gnatmem must be supplied with the @file{gmem.out} file and the executable to examine. If the location of @file{gmem.out} file was not explicitly supplied by @option{-i} switch, gnatmem will assume that this file can be found in the current directory. For example, after you have executed @file{my_program}, @file{gmem.out} can be analyzed by @code{gnatmem} using the command: @smallexample $ gnatmem my_program @end smallexample @noindent This will produce the output with the following format: *************** debut cc @smallexample $ gnatmem my_program Global information ------------------ Total number of allocations : 45 Total number of deallocations : 6 Final Water Mark (non freed mem) : 11.29 Kilobytes High Water Mark : 11.40 Kilobytes . . . Allocation Root # 2 ------------------- Number of non freed allocations : 11 Final Water Mark (non freed mem) : 1.16 Kilobytes High Water Mark : 1.27 Kilobytes Backtrace : my_program.adb:23 my_program.alloc . . . @end smallexample The first block of output gives general information. In this case, the Ada construct ``@code{@b{new}}'' was executed 45 times, and only 6 calls to an Unchecked_Deallocation routine occurred. @noindent Subsequent paragraphs display information on all allocation roots. An allocation root is a specific point in the execution of the program that generates some dynamic allocation, such as a ``@code{@b{new}}'' construct. This root is represented by an execution backtrace (or subprogram call stack). By default the backtrace depth for allocations roots is 1, so that a root corresponds exactly to a source location. The backtrace can be made deeper, to make the root more specific. @node Switches for gnatmem @subsection Switches for @code{gnatmem} @noindent @code{gnatmem} recognizes the following switches: @table @option @item -q @cindex @option{-q} (@code{gnatmem}) Quiet. Gives the minimum output needed to identify the origin of the memory leaks. Omits statistical information. @item @var{N} @cindex @var{N} (@code{gnatmem}) N is an integer literal (usually between 1 and 10) which controls the depth of the backtraces defining allocation root. The default value for N is 1. The deeper the backtrace, the more precise the localization of the root. Note that the total number of roots can depend on this parameter. This parameter must be specified @emph{before} the name of the executable to be analyzed, to avoid ambiguity. @item -b n @cindex @option{-b} (@code{gnatmem}) This switch has the same effect as just depth parameter. @item -i @var{file} @cindex @option{-i} (@code{gnatmem}) Do the @code{gnatmem} processing starting from @file{file}, rather than @file{gmem.out} in the current directory. @item -m n @cindex @option{-m} (@code{gnatmem}) This switch causes @code{gnatmem} to mask the allocation roots that have less than n leaks. The default value is 1. Specifying the value of 0 will allow to examine even the roots that didn't result in leaks. @item -s order @cindex @option{-s} (@code{gnatmem}) This switch causes @code{gnatmem} to sort the allocation roots according to the specified order of sort criteria, each identified by a single letter. The currently supported criteria are @code{n, h, w} standing respectively for number of unfreed allocations, high watermark, and final watermark corresponding to a specific root. The default order is @code{nwh}. @end table @node Example of gnatmem Usage @subsection Example of @code{gnatmem} Usage @noindent The following example shows the use of @code{gnatmem} on a simple memory-leaking program. Suppose that we have the following Ada program: @smallexample @c ada @group @cartouche with Unchecked_Deallocation; procedure Test_Gm is type T is array (1..1000) of Integer; type Ptr is access T; procedure Free is new Unchecked_Deallocation (T, Ptr); A : Ptr; procedure My_Alloc is begin A := new T; end My_Alloc; procedure My_DeAlloc is B : Ptr := A; begin Free (B); end My_DeAlloc; begin My_Alloc; for I in 1 .. 5 loop for J in I .. 5 loop My_Alloc; end loop; My_Dealloc; end loop; end; @end cartouche @end group @end smallexample @noindent The program needs to be compiled with debugging option and linked with @code{gmem} library: @smallexample $ gnatmake -g test_gm -largs -lgmem @end smallexample @noindent Then we execute the program as usual: @smallexample $ test_gm @end smallexample @noindent Then @code{gnatmem} is invoked simply with @smallexample $ gnatmem test_gm @end smallexample @noindent which produces the following output (result may vary on different platforms): @smallexample Global information ------------------ Total number of allocations : 18 Total number of deallocations : 5 Final Water Mark (non freed mem) : 53.00 Kilobytes High Water Mark : 56.90 Kilobytes Allocation Root # 1 ------------------- Number of non freed allocations : 11 Final Water Mark (non freed mem) : 42.97 Kilobytes High Water Mark : 46.88 Kilobytes Backtrace : test_gm.adb:11 test_gm.my_alloc Allocation Root # 2 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 10.02 Kilobytes High Water Mark : 10.02 Kilobytes Backtrace : s-secsta.adb:81 system.secondary_stack.ss_init Allocation Root # 3 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 12 Bytes High Water Mark : 12 Bytes Backtrace : s-secsta.adb:181 system.secondary_stack.ss_init @end smallexample @noindent Note that the GNAT run time contains itself a certain number of allocations that have no corresponding deallocation, as shown here for root #2 and root #3. This is a normal behavior when the number of non-freed allocations is one, it allocates dynamic data structures that the run time needs for the complete lifetime of the program. Note also that there is only one allocation root in the user program with a single line back trace: test_gm.adb:11 test_gm.my_alloc, whereas a careful analysis of the program shows that 'My_Alloc' is called at 2 different points in the source (line 21 and line 24). If those two allocation roots need to be distinguished, the backtrace depth parameter can be used: @smallexample $ gnatmem 3 test_gm @end smallexample @noindent which will give the following output: @smallexample Global information ------------------ Total number of allocations : 18 Total number of deallocations : 5 Final Water Mark (non freed mem) : 53.00 Kilobytes High Water Mark : 56.90 Kilobytes Allocation Root # 1 ------------------- Number of non freed allocations : 10 Final Water Mark (non freed mem) : 39.06 Kilobytes High Water Mark : 42.97 Kilobytes Backtrace : test_gm.adb:11 test_gm.my_alloc test_gm.adb:24 test_gm b_test_gm.c:52 main Allocation Root # 2 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 10.02 Kilobytes High Water Mark : 10.02 Kilobytes Backtrace : s-secsta.adb:81 system.secondary_stack.ss_init s-secsta.adb:283 b_test_gm.c:33 adainit Allocation Root # 3 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 3.91 Kilobytes High Water Mark : 3.91 Kilobytes Backtrace : test_gm.adb:11 test_gm.my_alloc test_gm.adb:21 test_gm b_test_gm.c:52 main Allocation Root # 4 ------------------- Number of non freed allocations : 1 Final Water Mark (non freed mem) : 12 Bytes High Water Mark : 12 Bytes Backtrace : s-secsta.adb:181 system.secondary_stack.ss_init s-secsta.adb:283 b_test_gm.c:33 adainit @end smallexample @noindent The allocation root #1 of the first example has been split in 2 roots #1 and #3 thanks to the more precise associated backtrace. @end ifclear @node Stack Related Facilities @chapter Stack Related Facilities @noindent This chapter describes some useful tools associated with stack checking and analysis. In particular, it deals with dynamic and static stack usage measurements. @menu * Stack Overflow Checking:: * Static Stack Usage Analysis:: * Dynamic Stack Usage Analysis:: @end menu @node Stack Overflow Checking @section Stack Overflow Checking @cindex Stack Overflow Checking @cindex -fstack-check @noindent For most operating systems, @command{gcc} does not perform stack overflow checking by default. This means that if the main environment task or some other task exceeds the available stack space, then unpredictable behavior will occur. Most native systems offer some level of protection by adding a guard page at the end of each task stack. This mechanism is usually not enough for dealing properly with stack overflow situations because a large local variable could ``jump'' above the guard page. Furthermore, when the guard page is hit, there may not be any space left on the stack for executing the exception propagation code. Enabling stack checking avoids such situations. To activate stack checking, compile all units with the gcc option @option{-fstack-check}. For example: @smallexample gcc -c -fstack-check package1.adb @end smallexample @noindent Units compiled with this option will generate extra instructions to check that any use of the stack (for procedure calls or for declaring local variables in declare blocks) does not exceed the available stack space. If the space is exceeded, then a @code{Storage_Error} exception is raised. For declared tasks, the stack size is controlled by the size given in an applicable @code{Storage_Size} pragma or by the value specified at bind time with @option{-d} (@pxref{Switches for gnatbind}) or is set to the default size as defined in the GNAT runtime otherwise. For the environment task, the stack size depends on system defaults and is unknown to the compiler. Stack checking may still work correctly if a fixed size stack is allocated, but this cannot be guaranteed. @ifclear vms To ensure that a clean exception is signalled for stack overflow, set the environment variable @env{GNAT_STACK_LIMIT} to indicate the maximum stack area that can be used, as in: @cindex GNAT_STACK_LIMIT @smallexample SET GNAT_STACK_LIMIT 1600 @end smallexample @noindent The limit is given in kilobytes, so the above declaration would set the stack limit of the environment task to 1.6 megabytes. Note that the only purpose of this usage is to limit the amount of stack used by the environment task. If it is necessary to increase the amount of stack for the environment task, then this is an operating systems issue, and must be addressed with the appropriate operating systems commands. @end ifclear @ifset vms To have a fixed size stack in the environment task, the stack must be put in the P0 address space and its size specified. Use these switches to create a p0 image: @smallexample gnatmake my_progs -largs "-Wl,--opt=STACK=4000,/p0image" @end smallexample @noindent The quotes are required to keep case. The number after @samp{STACK=} is the size of the environmental task stack in pagelets (512 bytes). In this example the stack size is about 2 megabytes. @noindent A consequence of the @option{/p0image} qualifier is also to makes RMS buffers be placed in P0 space. Refer to @cite{HP OpenVMS Linker Utility Manual} for more details about the @option{/p0image} qualifier and the @option{stack} option. @end ifset @node Static Stack Usage Analysis @section Static Stack Usage Analysis @cindex Static Stack Usage Analysis @cindex -fstack-usage @noindent A unit compiled with @option{-fstack-usage} will generate an extra file that specifies the maximum amount of stack used, on a per-function basis. The file has the same basename as the target object file with a @file{.su} extension. Each line of this file is made up of three fields: @itemize @item The name of the function. @item A number of bytes. @item One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. @end itemize The second field corresponds to the size of the known part of the function frame. The qualifier @code{static} means that the function frame size is purely static. It usually means that all local variables have a static size. In this case, the second field is a reliable measure of the function stack utilization. The qualifier @code{dynamic} means that the function frame size is not static. It happens mainly when some local variables have a dynamic size. When this qualifier appears alone, the second field is not a reliable measure of the function stack analysis. When it is qualified with @code{bounded}, it means that the second field is a reliable maximum of the function stack utilization. @node Dynamic Stack Usage Analysis @section Dynamic Stack Usage Analysis @noindent It is possible to measure the maximum amount of stack used by a task, by adding a switch to @command{gnatbind}, as: @smallexample $ gnatbind -u0 file @end smallexample @noindent With this option, at each task termination, its stack usage is output on @file{stderr}. It is not always convenient to output the stack usage when the program is still running. Hence, it is possible to delay this output until program termination. for a given number of tasks specified as the argument of the @option{-u} option. For instance: @smallexample $ gnatbind -u100 file @end smallexample @noindent will buffer the stack usage information of the first 100 tasks to terminate and output this info at program termination. Results are displayed in four columns: @noindent Index | Task Name | Stack Size | Stack Usage [Value +/- Variation] @noindent where: @table @emph @item Index is a number associated with each task. @item Task Name is the name of the task analyzed. @item Stack Size is the maximum size for the stack. @item Stack Usage is the measure done by the stack analyzer. In order to prevent overflow, the stack is not entirely analyzed, and it's not possible to know exactly how much has actually been used. The report thus contains the theoretical stack usage (Value) and the possible variation (Variation) around this value. @end table @noindent The environment task stack, e.g., the stack that contains the main unit, is only processed when the environment variable GNAT_STACK_LIMIT is set. @c ********************************* @c * GNATCHECK * @c ********************************* @node Verifying Properties Using gnatcheck @chapter Verifying Properties Using @command{gnatcheck} @findex gnatcheck @cindex @command{gnatcheck} @noindent The @command{gnatcheck} tool is an ASIS-based utility that checks properties of Ada source files according to a given set of semantic rules. @cindex ASIS In order to check compliance with a given rule, @command{gnatcheck} has to semantically analyze the Ada sources. Therefore, checks can only be performed on legal Ada units. Moreover, when a unit depends semantically upon units located outside the current directory, the source search path has to be provided when calling @command{gnatcheck}, either through a specified project file or through @command{gnatcheck} switches as described below. A number of rules are predefined in @command{gnatcheck} and are described later in this chapter. You can also add new rules, by modifying the @command{gnatcheck} code and rebuilding the tool. In order to add a simple rule making some local checks, a small amount of straightforward ASIS-based programming is usually needed. Project support for @command{gnatcheck} is provided by the GNAT driver (see @ref{The GNAT Driver and Project Files}). Invoking @command{gnatcheck} on the command line has the form: @smallexample @c $ gnatcheck @ovar{switches} @{@var{filename}@} @c @r{[}^-files^/FILES^=@{@var{arg_list_filename}@}@r{]} @c @r{[}-cargs @var{gcc_switches}@r{]} -rules @var{rule_options} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatcheck @r{[}@var{switches}@r{]} @{@var{filename}@} @r{[}^-files^/FILES^=@{@var{arg_list_filename}@}@r{]} @r{[}-cargs @var{gcc_switches}@r{]} -rules @var{rule_options} @end smallexample @noindent where @itemize @bullet @item @var{switches} specify the general tool options @item Each @var{filename} is the name (including the extension) of a source file to process. ``Wildcards'' are allowed, and the file name may contain path information. @item Each @var{arg_list_filename} is the name (including the extension) of a text file containing the names of the source files to process, separated by spaces or line breaks. @item @var{gcc_switches} is a list of switches for @command{gcc}. They will be passed on to all compiler invocations made by @command{gnatcheck} to generate the ASIS trees. Here you can provide @option{^-I^/INCLUDE_DIRS=^} switches to form the source search path, and use the @option{-gnatec} switch to set the configuration file, use the @option{-gnat05} switch if sources should be compiled in Ada 2005 mode etc. @item @var{rule_options} is a list of options for controlling a set of rules to be checked by @command{gnatcheck} (@pxref{gnatcheck Rule Options}). @end itemize @noindent Either a @file{@var{filename}} or an @file{@var{arg_list_filename}} must be supplied. @menu * Format of the Report File:: * General gnatcheck Switches:: * gnatcheck Rule Options:: * Adding the Results of Compiler Checks to gnatcheck Output:: * Project-Wide Checks:: * Rule exemption:: * Predefined Rules:: * Example of gnatcheck Usage:: @end menu @node Format of the Report File @section Format of the Report File @cindex Report file (for @code{gnatcheck}) @noindent The @command{gnatcheck} tool outputs on @file{stderr} all messages concerning rule violations except if running in quiet mode. It also creates a text file that contains the complete report of the last gnatcheck run. By default this file is named @file{^gnatcheck.out^GNATCHECK.OUT^} and it is located in the current directory; the @option{^-o^/OUTPUT^} option can be used to change the name and/or location of the report file. This report contains: @itemize @bullet @item general details of the @command{gnatcheck} run: date and time of the run, the version of the tool that has generated this report, full parameters of the @command{gnatcheck} invocation, reference to the list of checked sources and applied rules (coding standard); @item summary of the run (number of checked sources and detected violations); @item list of exempted coding standard violations; @item list of non-exempted coding standard violations; @item list of problems in the definition of exemption sections; @item list of language violations (compile-time errors) detected in processed sources; @end itemize @node General gnatcheck Switches @section General @command{gnatcheck} Switches @noindent The following switches control the general @command{gnatcheck} behavior @table @option @c !sort! @cindex @option{^-a^/ALL^} (@command{gnatcheck}) @item ^-a^/ALL^ Process all units including those with read-only ALI files such as those from the GNAT Run-Time library. @ifclear vms @ignore @cindex @option{-d} (@command{gnatcheck}) @item -d Debug mode @end ignore @cindex @option{-dd} (@command{gnatcheck}) @item -dd Progress indicator mode (for use in GPS). @end ifclear @cindex @option{^-h^/HELP^} (@command{gnatcheck}) @item ^-h^/HELP^ List the predefined and user-defined rules. For more details see @ref{Predefined Rules}. @cindex @option{^-l^/LOCS^} (@command{gnatcheck}) @item ^-l^/LOCS^ Use full source locations references in the report file. For a construct from a generic instantiation a full source location is a chain from the location of this construct in the generic unit to the place where this unit is instantiated. @cindex @option{^-log^/LOG^} (@command{gnatcheck}) @item ^-log^/LOG^ Duplicate all the output sent to @file{stderr} into a log file. The log file is named @file{gnatcheck.log} and is located in the current directory. @cindex @option{^-m^/DIAGNOSTIC_LIMIT^} (@command{gnatcheck}) @item ^-m@i{nnnn}^/DIAGNOSTIC_LIMIT=@i{nnnn}^ Maximum number of diagnostics to be sent to @file{stdout}, where @i{nnnn} is in the range 0@dots{}1000; the default value is 500. Zero means that there is no limitation on the number of diagnostic messages to be output. @cindex @option{^-q^/QUIET^} (@command{gnatcheck}) @item ^-q^/QUIET^ Quiet mode. All the diagnostics about rule violations are placed in the @command{gnatcheck} report file only, without duplication on @file{stdout}. @cindex @option{^-s^/SHORT^} (@command{gnatcheck}) @item ^-s^/SHORT^ Short format of the report file (no version information, no list of applied rules, no list of checked sources is included) @cindex @option{^--include-file=@var{file}^/INCLUDE_FILE=@var{file}^} (@command{gnatcheck}) @item ^--include-file^/INCLUDE_FILE^ Append the content of the specified text file to the report file @cindex @option{^-t^/TIME^} (@command{gnatcheck}) @item ^-t^/TIME^ Print out execution time. @cindex @option{^-v^/VERBOSE^} (@command{gnatcheck}) @item ^-v^/VERBOSE^ Verbose mode; @command{gnatcheck} generates version information and then a trace of sources being processed. @cindex @option{^-o ^/OUTPUT^} (@command{gnatcheck}) @item ^-o ^/OUTPUT=^@var{report_file} Set name of report file file to @var{report_file} . @end table @node gnatcheck Rule Options @section @command{gnatcheck} Rule Options @noindent The following options control the processing performed by @command{gnatcheck}. @table @option @cindex @option{+ALL} (@command{gnatcheck}) @item +ALL Turn all the rule checks ON. @cindex @option{-ALL} (@command{gnatcheck}) @item -ALL Turn all the rule checks OFF. @cindex @option{+R} (@command{gnatcheck}) @item +R@var{rule_id}@r{[}:@var{param}@r{]} Turn on the check for a specified rule with the specified parameter, if any. @var{rule_id} must be the identifier of one of the currently implemented rules (use @option{^-h^/HELP^} for the list of implemented rules). Rule identifiers are not case-sensitive. The @var{param} item must be a string representing a valid parameter(s) for the specified rule. If it contains any space characters then this string must be enclosed in quotation marks. @cindex @option{-R} (@command{gnatcheck}) @item -R@var{rule_id}@r{[}:@var{param}@r{]} Turn off the check for a specified rule with the specified parameter, if any. @cindex @option{-from} (@command{gnatcheck}) @item -from=@var{rule_option_filename} Read the rule options from the text file @var{rule_option_filename}, referred to as a ``coding standard file'' below. @end table @noindent The default behavior is that all the rule checks are disabled. A coding standard file is a text file that contains a set of rule options described above. @cindex Coding standard file (for @code{gnatcheck}) The file may contain empty lines and Ada-style comments (comment lines and end-of-line comments). There can be several rule options on a single line (separated by a space). A coding standard file may reference other coding standard files by including more @option{-from=@var{rule_option_filename}} options, each such option being replaced with the content of the corresponding coding standard file during processing. In case a cycle is detected (that is, @file{@var{rule_file_1}} reads rule options from @file{@var{rule_file_2}}, and @file{@var{rule_file_2}} reads (directly or indirectly) rule options from @file{@var{rule_file_1}}), processing fails with an error message. @node Adding the Results of Compiler Checks to gnatcheck Output @section Adding the Results of Compiler Checks to @command{gnatcheck} Output @noindent The @command{gnatcheck} tool can include in the generated diagnostic messages and in the report file the results of the checks performed by the compiler. Though disabled by default, this effect may be obtained by using @option{+R} with the following rule identifiers and parameters: @table @option @item Restrictions To record restrictions violations (which are performed by the compiler if the pragma @code{Restrictions} or @code{Restriction_Warnings} are given), use the @code{Restrictions} rule with the same parameters as pragma @code{Restrictions} or @code{Restriction_Warnings}. @item Style_Checks To record compiler style checks (@pxref{Style Checking}), use the @code{Style_Checks} rule. This rule takes a parameter in one of the following forms: @itemize @item @code{All_Checks}, which enables the standard style checks corresponding to the @option{-gnatyy} GNAT style check option, or @item a string with the same structure and semantics as the @code{string_LITERAL} parameter of the GNAT pragma @code{Style_Checks} (for further information about this pragma, @pxref{Pragma Style_Checks,,, gnat_rm, GNAT Reference Manual}). @end itemize @noindent For example, the @code{+RStyle_Checks:O} rule option activates the compiler style check that corresponds to @code{-gnatyO} style check option. @item Warnings To record compiler warnings (@pxref{Warning Message Control}), use the @code{Warnings} rule with a parameter that is a valid @i{static_string_expression} argument of the GNAT pragma @code{Warnings} (for further information about this pragma, @pxref{Pragma Warnings,,,gnat_rm, GNAT Reference Manual}). Note that in case of gnatcheck 's' parameter, that corresponds to the GNAT @option{-gnatws} option, disables all the specific warnings, but not suppresses the warning mode, and 'e' parameter, corresponding to @option{-gnatwe} that means "treat warnings as errors", does not have any effect. @end table To disable a specific restriction check, use @code{-RStyle_Checks} gnatcheck option with the corresponding restriction name as a parameter. @code{-R} is not available for @code{Style_Checks} and @code{Warnings} options, to disable warnings and style checks, use the corresponding warning and style options. @node Project-Wide Checks @section Project-Wide Checks @cindex Project-wide checks (for @command{gnatcheck}) @noindent In order to perform checks on all units of a given project, you can use the GNAT driver along with the @option{-P} option: @smallexample gnat check -Pproj -rules -from=my_rules @end smallexample @noindent If the project @code{proj} depends upon other projects, you can perform checks on the project closure using the @option{-U} option: @smallexample gnat check -Pproj -U -rules -from=my_rules @end smallexample @noindent Finally, if not all the units are relevant to a particular main program in the project closure, you can perform checks for the set of units needed to create a given main program (unit closure) using the @option{-U} option followed by the name of the main unit: @smallexample gnat check -Pproj -U main -rules -from=my_rules @end smallexample @node Rule exemption @section Rule exemption @cindex Rule exemption (for @command{gnatcheck}) @noindent One of the most useful applications of @command{gnatcheck} is to automate the enforcement of project-specific coding standards, for example in safety-critical systems where particular features must be restricted in order to simplify the certification effort. However, it may sometimes be appropriate to violate a coding standard rule, and in such cases the rationale for the violation should be provided in the source program itself so that the individuals reviewing or maintaining the program can immediately understand the intent. The @command{gnatcheck} tool supports this practice with the notion of a ``rule exemption'' covering a specific source code section. Normally rule violation messages are issued both on @file{stderr} and in a report file. In contrast, exempted violations are not listed on @file{stderr}; thus users invoking @command{gnatcheck} interactively (e.g. in its GPS interface) do not need to pay attention to known and justified violations. However, exempted violations along with their justification are documented in a special section of the report file that @command{gnatcheck} generates. @menu * Using pragma Annotate to Control Rule Exemption:: * gnatcheck Annotations Rules:: @end menu @node Using pragma Annotate to Control Rule Exemption @subsection Using pragma @code{Annotate} to Control Rule Exemption @cindex Using pragma Annotate to control rule exemption @noindent Rule exemption is controlled by pragma @code{Annotate} when its first argument is ``gnatcheck''. The syntax of @command{gnatcheck}'s exemption control annotations is as follows: @smallexample @c ada @group pragma Annotate (gnatcheck, @i{exemption_control}, @i{Rule_Name}, [@i{justification}]); @i{exemption_control} ::= Exempt_On | Exempt_Off @i{Rule_Name} ::= string_literal @i{justification} ::= string_literal @end group @end smallexample @noindent When a @command{gnatcheck} annotation has more then four arguments, @command{gnatcheck} issues a warning and ignores the additional arguments. If the additional arguments do not follow the syntax above, @command{gnatcheck} emits a warning and ignores the annotation. The @i{@code{Rule_Name}} argument should be the name of some existing @command{gnatcheck} rule. Otherwise a warning message is generated and the pragma is ignored. If @code{Rule_Name} denotes a rule that is not activated by the given @command{gnatcheck} call, the pragma is ignored and no warning is issued. A source code section where an exemption is active for a given rule is delimited by an @code{exempt_on} and @code{exempt_off} annotation pair: @smallexample @c ada pragma Annotate (gnatcheck, Exempt_On, Rule_Name, "justification"); -- source code section pragma Annotate (gnatcheck, Exempt_Off, Rule_Name); @end smallexample @node gnatcheck Annotations Rules @subsection @command{gnatcheck} Annotations Rules @cindex @command{gnatcheck} annotations rules @itemize @bullet @item An ``Exempt_Off'' annotation can only appear after a corresponding ``Exempt_On'' annotation. @item Exempted source code sections are only based on the source location of the annotations. Any source construct between the two annotations is part of the exempted source code section. @item Exempted source code sections for different rules are independent. They can be nested or intersect with one another without limitation. Creating nested or intersecting source code sections for the same rule is not allowed. @item Malformed exempted source code sections are reported by a warning, and the corresponding rule exemptions are ignored. @item When an exempted source code section does not contain at least one violation of the exempted rule, a warning is emitted on @file{stderr}. @item If an ``Exempt_On'' annotation pragma does not have a matching ``Exempt_Off'' annotation pragma in the same compilation unit, then the exemption for the given rule is ignored and a warning is issued. @end itemize @node Predefined Rules @section Predefined Rules @cindex Predefined rules (for @command{gnatcheck}) @ignore @c (Jan 2007) Since the global rules are still under development and are not @c documented, there is no point in explaining the difference between @c global and local rules @noindent A rule in @command{gnatcheck} is either local or global. A @emph{local rule} is a rule that applies to a well-defined section of a program and that can be checked by analyzing only this section. A @emph{global rule} requires analysis of some global properties of the whole program (mostly related to the program call graph). As of @value{NOW}, the implementation of global rules should be considered to be at a preliminary stage. You can use the @option{+GLOBAL} option to enable all the global rules, and the @option{-GLOBAL} rule option to disable all the global rules. All the global rules in the list below are so indicated by marking them ``GLOBAL''. This +GLOBAL and -GLOBAL options are not included in the list of gnatcheck options above, because at the moment they are considered as a temporary debug options. @command{gnatcheck} performs rule checks for generic instances only for global rules. This limitation may be relaxed in a later release. @end ignore @noindent The predefined rules implemented in @command{gnatcheck} are described in a companion document, @cite{GNATcheck Reference Manual -- Predefined Rules}. The rule identifier is used as a parameter of @command{gnatcheck}'s @option{+R} or @option{-R} switches. @node Example of gnatcheck Usage @section Example of @command{gnatcheck} Usage @noindent Here is a simple example. Suppose that in the current directory we have a project file named @file{gnatcheck_example.gpr} with the following content: @smallexample @c projectfile project Gnatcheck_Example is for Source_Dirs use ("src"); for Object_Dir use "obj"; for Main use ("main.adb"); package Check is for Default_Switches ("ada") use ("-rules", "-from=coding_standard"); end Check; end Gnatcheck_Example; @end smallexample @noindent And the file named @file{coding_standard} is also located in the current directory and has the following content: @smallexample ----------------------------------------------------- -- This is a sample gnatcheck coding standard file -- ----------------------------------------------------- -- First, turning on rules, that are directly implemented in gnatcheck +RAbstract_Type_Declarations +RAnonymous_Arrays +RLocal_Packages +RFloat_Equality_Checks +REXIT_Statements_With_No_Loop_Name -- Then, activating compiler checks of interest: +RStyle_Checks:e -- This style check checks if a unit name is present on END keyword that -- is the end of the unit declaration @end smallexample @noindent And the subdirectory @file{src} contains the following Ada sources: @file{pack.ads}: @smallexample @c ada package Pack is type T is abstract tagged private; procedure P (X : T) is abstract; package Inner is type My_Float is digits 8; function Is_Equal (L, R : My_Float) return Boolean; end Inner; private type T is abstract tagged null record; end; @end smallexample @noindent @file{pack.adb}: @smallexample @c ada package body Pack is package body Inner is function Is_Equal (L, R : My_Float) return Boolean is begin return L = R; end; end Inner; end Pack; @end smallexample @noindent and @file{main.adb} @smallexample @c ada with Pack; use Pack; procedure Main is pragma Annotate (gnatcheck, Exempt_On, "Anonymous_Arrays", "this one is fine"); Float_Array : array (1 .. 10) of Inner.My_Float; pragma Annotate (gnatcheck, Exempt_Off, "Anonymous_Arrays"); Another_Float_Array : array (1 .. 10) of Inner.My_Float; use Inner; B : Boolean := False; begin for J in Float_Array'Range loop if Is_Equal (Float_Array (J), Another_Float_Array (J)) then B := True; exit; end if; end loop; end Main; @end smallexample @noindent And suppose we call @command{gnatcheck} from the current directory using the @command{gnat} driver: @smallexample gnat check -Pgnatcheck_example.gpr @end smallexample @noindent As a result, @command{gnatcheck} is called to check all the files from the project @file{gnatcheck_example.gpr} using the coding standard defined by the file @file{coding_standard}. As the result, the @command{gnatcheck} report file named @file{gnatcheck.out} will be created in the current directory, and it will have the following content: @smallexample RULE CHECKING REPORT 1. OVERVIEW Date and time of execution: 2009.10.28 14:17 Tool version: GNATCHECK (built with ASIS 2.0.R for GNAT Pro 6.3.0w (20091016)) Command line: gnatcheck -files=.../GNAT-TEMP-000004.TMP -cargs -gnatec=.../GNAT-TEMP-000003.TMP -rules -from=coding_standard Coding standard (applied rules): Abstract_Type_Declarations Anonymous_Arrays EXIT_Statements_With_No_Loop_Name Float_Equality_Checks Local_Packages Compiler style checks: -gnatye Number of coding standard violations: 6 Number of exempted coding standard violations: 1 2. DETECTED RULE VIOLATIONS 2.1. NON-EXEMPTED VIOLATIONS Source files with non-exempted violations pack.ads pack.adb main.adb List of violations grouped by files, and ordered by increasing source location: pack.ads:2:4: declaration of abstract type pack.ads:5:4: declaration of local package pack.ads:10:30: declaration of abstract type pack.ads:11:1: (style) "end Pack" required pack.adb:5:19: use of equality operation for float values pack.adb:6:7: (style) "end Is_Equal" required main.adb:9:26: anonymous array type main.adb:19:10: exit statement with no loop name 2.2. EXEMPTED VIOLATIONS Source files with exempted violations main.adb List of violations grouped by files, and ordered by increasing source location: main.adb:6:18: anonymous array type (this one is fine) 2.3. SOURCE FILES WITH NO VIOLATION No files without violations END OF REPORT @end smallexample @c ********************************* @node Creating Sample Bodies Using gnatstub @chapter Creating Sample Bodies Using @command{gnatstub} @findex gnatstub @noindent @command{gnatstub} creates body stubs, that is, empty but compilable bodies for library unit declarations. Note: to invoke @code{gnatstub} with a project file, use the @code{gnat} driver (see @ref{The GNAT Driver and Project Files}). To create a body stub, @command{gnatstub} has to compile the library unit declaration. Therefore, bodies can be created only for legal library units. Moreover, if a library unit depends semantically upon units located outside the current directory, you have to provide the source search path when calling @command{gnatstub}, see the description of @command{gnatstub} switches below. By default, all the program unit body stubs generated by @code{gnatstub} raise the predefined @code{Program_Error} exception, which will catch accidental calls of generated stubs. This behavior can be changed with option @option{^--no-exception^/NO_EXCEPTION^} (see below). @menu * Running gnatstub:: * Switches for gnatstub:: @end menu @node Running gnatstub @section Running @command{gnatstub} @noindent @command{gnatstub} has the command-line interface of the form @smallexample @c $ gnatstub @ovar{switches} @var{filename} @ovar{directory} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatstub @r{[}@var{switches}@r{]} @var{filename} @r{[}@var{directory}@r{]} @r{[}-cargs @var{gcc_switches}@r{]} @end smallexample @noindent where @table @var @item filename is the name of the source file that contains a library unit declaration for which a body must be created. The file name may contain the path information. The file name does not have to follow the GNAT file name conventions. If the name does not follow GNAT file naming conventions, the name of the body file must be provided explicitly as the value of the @option{^-o^/BODY=^@var{body-name}} option. If the file name follows the GNAT file naming conventions and the name of the body file is not provided, @command{gnatstub} creates the name of the body file from the argument file name by replacing the @file{.ads} suffix with the @file{.adb} suffix. @item directory indicates the directory in which the body stub is to be placed (the default is the current directory) @item @samp{@var{gcc_switches}} is a list of switches for @command{gcc}. They will be passed on to all compiler invocations made by @command{gnatelim} to generate the ASIS trees. Here you can provide @option{^-I^/INCLUDE_DIRS=^} switches to form the source search path, use the @option{-gnatec} switch to set the configuration file, use the @option{-gnat05} switch if sources should be compiled in Ada 2005 mode etc. @item switches is an optional sequence of switches as described in the next section @end table @node Switches for gnatstub @section Switches for @command{gnatstub} @table @option @c !sort! @item ^-f^/FULL^ @cindex @option{^-f^/FULL^} (@command{gnatstub}) If the destination directory already contains a file with the name of the body file for the argument spec file, replace it with the generated body stub. @item ^-hs^/HEADER=SPEC^ @cindex @option{^-hs^/HEADER=SPEC^} (@command{gnatstub}) Put the comment header (i.e., all the comments preceding the compilation unit) from the source of the library unit declaration into the body stub. @item ^-hg^/HEADER=GENERAL^ @cindex @option{^-hg^/HEADER=GENERAL^} (@command{gnatstub}) Put a sample comment header into the body stub. @item ^--header-file=@var{filename}^/FROM_HEADER_FILE=@var{filename}^ @cindex @option{^--header-file^/FROM_HEADER_FILE=^} (@command{gnatstub}) Use the content of the file as the comment header for a generated body stub. @ifclear vms @item -IDIR @cindex @option{-IDIR} (@command{gnatstub}) @itemx -I- @cindex @option{-I-} (@command{gnatstub}) @end ifclear @ifset vms @item /NOCURRENT_DIRECTORY @cindex @option{/NOCURRENT_DIRECTORY} (@command{gnatstub}) @end ifset ^These switches have ^This switch has^ the same meaning as in calls to @command{gcc}. ^They define ^It defines ^ the source search path in the call to @command{gcc} issued by @command{gnatstub} to compile an argument source file. @item ^-gnatec^/CONFIGURATION_PRAGMAS_FILE=^@var{PATH} @cindex @option{^-gnatec^/CONFIGURATION_PRAGMAS_FILE^} (@command{gnatstub}) This switch has the same meaning as in calls to @command{gcc}. It defines the additional configuration file to be passed to the call to @command{gcc} issued by @command{gnatstub} to compile an argument source file. @item ^-gnatyM^/MAX_LINE_LENGTH=^@var{n} @cindex @option{^-gnatyM^/MAX_LINE_LENGTH^} (@command{gnatstub}) (@var{n} is a non-negative integer). Set the maximum line length in the body stub to @var{n}; the default is 79. The maximum value that can be specified is 32767. Note that in the special case of configuration pragma files, the maximum is always 32767 regardless of whether or not this switch appears. @item ^-gnaty^/STYLE_CHECKS=^@var{n} @cindex @option{^-gnaty^/STYLE_CHECKS=^} (@command{gnatstub}) (@var{n} is a non-negative integer from 1 to 9). Set the indentation level in the generated body sample to @var{n}. The default indentation is 3. @item ^-gnatyo^/ORDERED_SUBPROGRAMS^ @cindex @option{^-gnato^/ORDERED_SUBPROGRAMS^} (@command{gnatstub}) Order local bodies alphabetically. (By default local bodies are ordered in the same way as the corresponding local specs in the argument spec file.) @item ^-i^/INDENTATION=^@var{n} @cindex @option{^-i^/INDENTATION^} (@command{gnatstub}) Same as @option{^-gnaty^/STYLE_CHECKS=^@var{n}} @item ^-k^/TREE_FILE=SAVE^ @cindex @option{^-k^/TREE_FILE=SAVE^} (@command{gnatstub}) Do not remove the tree file (i.e., the snapshot of the compiler internal structures used by @command{gnatstub}) after creating the body stub. @item ^-l^/LINE_LENGTH=^@var{n} @cindex @option{^-l^/LINE_LENGTH^} (@command{gnatstub}) Same as @option{^-gnatyM^/MAX_LINE_LENGTH=^@var{n}} @item ^--no-exception^/NO_EXCEPTION^ @cindex @option{^--no-exception^/NO_EXCEPTION^} (@command{gnatstub}) Avoind raising PROGRAM_ERROR in the generated bodies of program unit stubs. This is not always possible for function stubs. @item ^--no-local-header^/NO_LOCAL_HEADER^ @cindex @option{^--no-local-header^/NO_LOCAL_HEADER^} (@command{gnatstub}) Do not place local comment header with unit name before body stub for a unit. @item ^-o ^/BODY=^@var{body-name} @cindex @option{^-o^/BODY^} (@command{gnatstub}) Body file name. This should be set if the argument file name does not follow the GNAT file naming conventions. If this switch is omitted the default name for the body will be obtained from the argument file name according to the GNAT file naming conventions. @item ^-q^/QUIET^ @cindex @option{^-q^/QUIET^} (@command{gnatstub}) Quiet mode: do not generate a confirmation when a body is successfully created, and do not generate a message when a body is not required for an argument unit. @item ^-r^/TREE_FILE=REUSE^ @cindex @option{^-r^/TREE_FILE=REUSE^} (@command{gnatstub}) Reuse the tree file (if it exists) instead of creating it. Instead of creating the tree file for the library unit declaration, @command{gnatstub} tries to find it in the current directory and use it for creating a body. If the tree file is not found, no body is created. This option also implies @option{^-k^/SAVE^}, whether or not the latter is set explicitly. @item ^-t^/TREE_FILE=OVERWRITE^ @cindex @option{^-t^/TREE_FILE=OVERWRITE^} (@command{gnatstub}) Overwrite the existing tree file. If the current directory already contains the file which, according to the GNAT file naming rules should be considered as a tree file for the argument source file, @command{gnatstub} will refuse to create the tree file needed to create a sample body unless this option is set. @item ^-v^/VERBOSE^ @cindex @option{^-v^/VERBOSE^} (@command{gnatstub}) Verbose mode: generate version information. @end table @c ********************************* @node Generating Ada Bindings for C and C++ headers @chapter Generating Ada Bindings for C and C++ headers @findex binding @noindent GNAT now comes with a binding generator for C and C++ headers which is intended to do 95% of the tedious work of generating Ada specs from C or C++ header files. Note that this capability is not intended to generate 100% correct Ada specs, and will is some cases require manual adjustments, although it can often be used out of the box in practice. Some of the known limitations include: @itemize @bullet @item only very simple character constant macros are translated into Ada constants. Function macros (macros with arguments) are partially translated as comments, to be completed manually if needed. @item some extensions (e.g. vector types) are not supported @item pointers to pointers or complex structures are mapped to System.Address @item identifiers with identical name (except casing) will generate compilation errors (e.g. @code{shm_get} vs @code{SHM_GET}). @end itemize The code generated is using the Ada 2005 syntax, which makes it easier to interface with other languages than previous versions of Ada. @menu * Running the binding generator:: * Generating bindings for C++ headers:: * Switches:: @end menu @node Running the binding generator @section Running the binding generator @noindent The binding generator is part of the @command{gcc} compiler and can be invoked via the @option{-fdump-ada-spec} switch, which will generate Ada spec files for the header files specified on the command line, and all header files needed by these files transitivitely. For example: @smallexample $ g++ -c -fdump-ada-spec -C /usr/include/time.h $ gcc -c -gnat05 *.ads @end smallexample will generate, under GNU/Linux, the following files: @file{time_h.ads}, @file{bits_time_h.ads}, @file{stddef_h.ads}, @file{bits_types_h.ads} which correspond to the files @file{/usr/include/time.h}, @file{/usr/include/bits/time.h}, etc@dots{}, and will then compile in Ada 2005 mode these Ada specs. The @code{-C} switch tells @command{gcc} to extract comments from headers, and will attempt to generate corresponding Ada comments. If you want to generate a single Ada file and not the transitive closure, you can use instead the @option{-fdump-ada-spec-slim} switch. Note that we recommend when possible to use the @command{g++} driver to generate bindings, even for most C headers, since this will in general generate better Ada specs. For generating bindings for C++ headers, it is mandatory to use the @command{g++} command, or @command{gcc -x c++} which is equivalent in this case. If @command{g++} cannot work on your C headers because of incompatibilities between C and C++, then you can fallback to @command{gcc} instead. For an example of better bindings generated from the C++ front-end, the name of the parameters (when available) are actually ignored by the C front-end. Consider the following C header: @smallexample extern void foo (int variable); @end smallexample with the C front-end, @code{variable} is ignored, and the above is handled as: @smallexample extern void foo (int); @end smallexample generating a generic: @smallexample procedure foo (param1 : int); @end smallexample with the C++ front-end, the name is available, and we generate: @smallexample procedure foo (variable : int); @end smallexample In some cases, the generated bindings will be more complete or more meaningful when defining some macros, which you can do via the @option{-D} switch. This is for example the case with @file{Xlib.h} under GNU/Linux: @smallexample g++ -c -fdump-ada-spec -DXLIB_ILLEGAL_ACCESS -C /usr/include/X11/Xlib.h @end smallexample The above will generate more complete bindings than a straight call without the @option{-DXLIB_ILLEGAL_ACCESS} switch. In other cases, it is not possible to parse a header file in a stand alone manner, because other include files need to be included first. In this case, the solution is to create a small header file including the needed @code{#include} and possible @code{#define} directives. For example, to generate Ada bindings for @file{readline/readline.h}, you need to first include @file{stdio.h}, so you can create a file with the following two lines in e.g. @file{readline1.h}: @smallexample #include #include @end smallexample and then generate Ada bindings from this file: @smallexample $ g++ -c -fdump-ada-spec readline1.h @end smallexample @node Generating bindings for C++ headers @section Generating bindings for C++ headers @noindent Generating bindings for C++ headers is done using the same options, always with the @command{g++} compiler. In this mode, C++ classes will be mapped to Ada tagged types, constructors will be mapped using the @code{CPP_Constructor} pragma, and when possible, multiple inheritance of abstract classes will be mapped to Ada interfaces (@xref{Interfacing to C++,,,gnat_rm, GNAT Reference Manual}, for additional information on interfacing to C++). For example, given the following C++ header file: @smallexample @group @cartouche class Carnivore @{ public: virtual int Number_Of_Teeth () = 0; @}; class Domestic @{ public: virtual void Set_Owner (char* Name) = 0; @}; class Animal @{ public: int Age_Count; virtual void Set_Age (int New_Age); @}; class Dog : Animal, Carnivore, Domestic @{ public: int Tooth_Count; char *Owner; virtual int Number_Of_Teeth (); virtual void Set_Owner (char* Name); Dog(); @}; @end cartouche @end group @end smallexample The corresponding Ada code is generated: @smallexample @c ada @group @cartouche package Class_Carnivore is type Carnivore is limited interface; pragma Import (CPP, Carnivore); function Number_Of_Teeth (this : access Carnivore) return int is abstract; end; use Class_Carnivore; package Class_Domestic is type Domestic is limited interface; pragma Import (CPP, Domestic); procedure Set_Owner (this : access Domestic; Name : Interfaces.C.Strings.chars_ptr) is abstract; end; use Class_Domestic; package Class_Animal is type Animal is tagged limited record Age_Count : aliased int; end record; pragma Import (CPP, Animal); procedure Set_Age (this : access Animal; New_Age : int); pragma Import (CPP, Set_Age, "_ZN6Animal7Set_AgeEi"); end; use Class_Animal; package Class_Dog is type Dog is new Animal and Carnivore and Domestic with record Tooth_Count : aliased int; Owner : Interfaces.C.Strings.chars_ptr; end record; pragma Import (CPP, Dog); function Number_Of_Teeth (this : access Dog) return int; pragma Import (CPP, Number_Of_Teeth, "_ZN3Dog15Number_Of_TeethEv"); procedure Set_Owner (this : access Dog; Name : Interfaces.C.Strings.chars_ptr); pragma Import (CPP, Set_Owner, "_ZN3Dog9Set_OwnerEPc"); function New_Dog return Dog; pragma CPP_Constructor (New_Dog); pragma Import (CPP, New_Dog, "_ZN3DogC1Ev"); end; use Class_Dog; @end cartouche @end group @end smallexample @node Switches @section Switches @table @option @item -fdump-ada-spec @cindex @option{-fdump-ada-spec} (@command{gcc}) Generate Ada spec files for the given header files transitively (including all header files that these headers depend upon). @item -fdump-ada-spec-slim @cindex @option{-fdump-ada-spec-slim} (@command{gcc}) Generate Ada spec files for the header files specified on the command line only. @item -C @cindex @option{-C} (@command{gcc}) Extract comments from headers and generate Ada comments in the Ada spec files. @end table @node Other Utility Programs @chapter Other Utility Programs @noindent This chapter discusses some other utility programs available in the Ada environment. @menu * Using Other Utility Programs with GNAT:: * The External Symbol Naming Scheme of GNAT:: * Converting Ada Files to html with gnathtml:: * Installing gnathtml:: @ifset vms * LSE:: * Profiling:: @end ifset @end menu @node Using Other Utility Programs with GNAT @section Using Other Utility Programs with GNAT @noindent The object files generated by GNAT are in standard system format and in particular the debugging information uses this format. This means programs generated by GNAT can be used with existing utilities that depend on these formats. @ifclear vms In general, any utility program that works with C will also often work with Ada programs generated by GNAT. This includes software utilities such as gprof (a profiling program), @code{gdb} (the FSF debugger), and utilities such as Purify. @end ifclear @node The External Symbol Naming Scheme of GNAT @section The External Symbol Naming Scheme of GNAT @noindent In order to interpret the output from GNAT, when using tools that are originally intended for use with other languages, it is useful to understand the conventions used to generate link names from the Ada entity names. All link names are in all lowercase letters. With the exception of library procedure names, the mechanism used is simply to use the full expanded Ada name with dots replaced by double underscores. For example, suppose we have the following package spec: @smallexample @c ada @group @cartouche package QRS is MN : Integer; end QRS; @end cartouche @end group @end smallexample @noindent The variable @code{MN} has a full expanded Ada name of @code{QRS.MN}, so the corresponding link name is @code{qrs__mn}. @findex Export Of course if a @code{pragma Export} is used this may be overridden: @smallexample @c ada @group @cartouche package Exports is Var1 : Integer; pragma Export (Var1, C, External_Name => "var1_name"); Var2 : Integer; pragma Export (Var2, C, Link_Name => "var2_link_name"); end Exports; @end cartouche @end group @end smallexample @noindent In this case, the link name for @var{Var1} is whatever link name the C compiler would assign for the C function @var{var1_name}. This typically would be either @var{var1_name} or @var{_var1_name}, depending on operating system conventions, but other possibilities exist. The link name for @var{Var2} is @var{var2_link_name}, and this is not operating system dependent. @findex _main One exception occurs for library level procedures. A potential ambiguity arises between the required name @code{_main} for the C main program, and the name we would otherwise assign to an Ada library level procedure called @code{Main} (which might well not be the main program). To avoid this ambiguity, we attach the prefix @code{_ada_} to such names. So if we have a library level procedure such as @smallexample @c ada @group @cartouche procedure Hello (S : String); @end cartouche @end group @end smallexample @noindent the external name of this procedure will be @var{_ada_hello}. @node Converting Ada Files to html with gnathtml @section Converting Ada Files to HTML with @code{gnathtml} @noindent This @code{Perl} script allows Ada source files to be browsed using standard Web browsers. For installation procedure, see the section @xref{Installing gnathtml}. Ada reserved keywords are highlighted in a bold font and Ada comments in a blue font. Unless your program was compiled with the gcc @option{-gnatx} switch to suppress the generation of cross-referencing information, user defined variables and types will appear in a different color; you will be able to click on any identifier and go to its declaration. The command line is as follow: @smallexample @c $ perl gnathtml.pl @ovar{^switches^options^} @var{ada-files} @c Expanding @ovar macro inline (explanation in macro def comments) $ perl gnathtml.pl @r{[}@var{^switches^options^}@r{]} @var{ada-files} @end smallexample @noindent You can pass it as many Ada files as you want. @code{gnathtml} will generate an html file for every ada file, and a global file called @file{index.htm}. This file is an index of every identifier defined in the files. The available ^switches^options^ are the following ones: @table @option @item -83 @cindex @option{-83} (@code{gnathtml}) Only the Ada 83 subset of keywords will be highlighted. @item -cc @var{color} @cindex @option{-cc} (@code{gnathtml}) This option allows you to change the color used for comments. The default value is green. The color argument can be any name accepted by html. @item -d @cindex @option{-d} (@code{gnathtml}) If the Ada files depend on some other files (for instance through @code{with} clauses, the latter files will also be converted to html. Only the files in the user project will be converted to html, not the files in the run-time library itself. @item -D @cindex @option{-D} (@code{gnathtml}) This command is the same as @option{-d} above, but @command{gnathtml} will also look for files in the run-time library, and generate html files for them. @item -ext @var{extension} @cindex @option{-ext} (@code{gnathtml}) This option allows you to change the extension of the generated HTML files. If you do not specify an extension, it will default to @file{htm}. @item -f @cindex @option{-f} (@code{gnathtml}) By default, gnathtml will generate html links only for global entities ('with'ed units, global variables and types,@dots{}). If you specify @option{-f} on the command line, then links will be generated for local entities too. @item -l @var{number} @cindex @option{-l} (@code{gnathtml}) If this ^switch^option^ is provided and @var{number} is not 0, then @code{gnathtml} will number the html files every @var{number} line. @item -I @var{dir} @cindex @option{-I} (@code{gnathtml}) Specify a directory to search for library files (@file{.ALI} files) and source files. You can provide several -I switches on the command line, and the directories will be parsed in the order of the command line. @item -o @var{dir} @cindex @option{-o} (@code{gnathtml}) Specify the output directory for html files. By default, gnathtml will saved the generated html files in a subdirectory named @file{html/}. @item -p @var{file} @cindex @option{-p} (@code{gnathtml}) If you are using Emacs and the most recent Emacs Ada mode, which provides a full Integrated Development Environment for compiling, checking, running and debugging applications, you may use @file{.gpr} files to give the directories where Emacs can find sources and object files. Using this ^switch^option^, you can tell gnathtml to use these files. This allows you to get an html version of your application, even if it is spread over multiple directories. @item -sc @var{color} @cindex @option{-sc} (@code{gnathtml}) This ^switch^option^ allows you to change the color used for symbol definitions. The default value is red. The color argument can be any name accepted by html. @item -t @var{file} @cindex @option{-t} (@code{gnathtml}) This ^switch^option^ provides the name of a file. This file contains a list of file names to be converted, and the effect is exactly as though they had appeared explicitly on the command line. This is the recommended way to work around the command line length limit on some systems. @end table @node Installing gnathtml @section Installing @code{gnathtml} @noindent @code{Perl} needs to be installed on your machine to run this script. @code{Perl} is freely available for almost every architecture and Operating System via the Internet. On Unix systems, you may want to modify the first line of the script @code{gnathtml}, to explicitly tell the Operating system where Perl is. The syntax of this line is: @smallexample #!full_path_name_to_perl @end smallexample @noindent Alternatively, you may run the script using the following command line: @smallexample @c $ perl gnathtml.pl @ovar{switches} @var{files} @c Expanding @ovar macro inline (explanation in macro def comments) $ perl gnathtml.pl @r{[}@var{switches}@r{]} @var{files} @end smallexample @ifset vms @node LSE @section LSE @findex LSE @noindent The GNAT distribution provides an Ada 95 template for the HP Language Sensitive Editor (LSE), a component of DECset. In order to access it, invoke LSE with the qualifier /ENVIRONMENT=GNU:[LIB]ADA95.ENV. @node Profiling @section Profiling @findex PCA @noindent GNAT supports The HP Performance Coverage Analyzer (PCA), a component of DECset. To use it proceed as outlined under ``HELP PCA'', except for running the collection phase with the /DEBUG qualifier. @smallexample $ GNAT MAKE /DEBUG $ DEFINE LIB$DEBUG PCA$COLLECTOR $ RUN/DEBUG @end smallexample @noindent @end ifset @ifclear vms @c ****************************** @node Code Coverage and Profiling @chapter Code Coverage and Profiling @cindex Code Coverage @cindex Profiling @noindent This chapter describes how to use @code{gcov} - coverage testing tool - and @code{gprof} - profiler tool - on your Ada programs. @menu * Code Coverage of Ada Programs using gcov:: * Profiling an Ada Program using gprof:: @end menu @node Code Coverage of Ada Programs using gcov @section Code Coverage of Ada Programs using gcov @cindex gcov @cindex -fprofile-arcs @cindex -ftest-coverage @cindex -coverage @cindex Code Coverage @noindent @code{gcov} is a test coverage program: it analyzes the execution of a given program on selected tests, to help you determine the portions of the program that are still untested. @code{gcov} is part of the GCC suite, and is described in detail in the GCC User's Guide. You can refer to this documentation for a more complete description. This chapter provides a quick startup guide, and details some Gnat-specific features. @menu * Quick startup guide:: * Gnat specifics:: @end menu @node Quick startup guide @subsection Quick startup guide In order to perform coverage analysis of a program using @code{gcov}, 3 steps are needed: @itemize @bullet @item Code instrumentation during the compilation process @item Execution of the instrumented program @item Execution of the @code{gcov} tool to generate the result. @end itemize The code instrumentation needed by gcov is created at the object level: The source code is not modified in any way, because the instrumentation code is inserted by gcc during the compilation process. To compile your code with code coverage activated, you need to recompile your whole project using the switches @code{-fprofile-arcs} and @code{-ftest-coverage}, and link it using @code{-fprofile-arcs}. @smallexample $ gnatmake -P my_project.gpr -f -cargs -fprofile-arcs -ftest-coverage \ -largs -fprofile-arcs @end smallexample This compilation process will create @file{.gcno} files together with the usual object files. Once the program is compiled with coverage instrumentation, you can run it as many times as needed - on portions of a test suite for example. The first execution will produce @file{.gcda} files at the same location as the @file{.gcno} files. The following executions will update those files, so that a cumulative result of the covered portions of the program is generated. Finally, you need to call the @code{gcov} tool. The different options of @code{gcov} are available in the GCC User's Guide, section 'Invoking gcov'. This will create annotated source files with a @file{.gcov} extension: @file{my_main.adb} file will be analysed in @file{my_main.adb.gcov}. @node Gnat specifics @subsection Gnat specifics Because Ada semantics, portions of the source code may be shared among several object files. This is the case for example when generics are involved, when inlining is active or when declarations generate initialisation calls. In order to take into account this shared code, you need to call @code{gcov} on all source files of the tested program at once. The list of source files might exceed the system's maximum command line length. In order to bypass this limitation, a new mechanism has been implemented in @code{gcov}: you can now list all your project's files into a text file, and provide this file to gcov as a parameter, preceded by a @@ (e.g. @samp{gcov @@mysrclist.txt}). Note that on AIX compiling a static library with @code{-fprofile-arcs} is not supported as there can be unresolved symbols during the final link. @node Profiling an Ada Program using gprof @section Profiling an Ada Program using gprof @cindex gprof @cindex -pg @cindex Profiling @noindent This section is not meant to be an exhaustive documentation of @code{gprof}. Full documentation for it can be found in the GNU Profiler User's Guide documentation that is part of this GNAT distribution. Profiling a program helps determine the parts of a program that are executed most often, and are therefore the most time-consuming. @code{gprof} is the standard GNU profiling tool; it has been enhanced to better handle Ada programs and multitasking. It is currently supported on the following platforms @itemize @bullet @item linux x86/x86_64 @item solaris sparc/sparc64/x86 @item windows x86 @end itemize @noindent In order to profile a program using @code{gprof}, 3 steps are needed: @itemize @bullet @item Code instrumentation, requiring a full recompilation of the project with the proper switches. @item Execution of the program under the analysis conditions, i.e. with the desired input. @item Analysis of the results using the @code{gprof} tool. @end itemize @noindent The following sections detail the different steps, and indicate how to interpret the results: @menu * Compilation for profiling:: * Program execution:: * Running gprof:: * Interpretation of profiling results:: @end menu @node Compilation for profiling @subsection Compilation for profiling @cindex -pg @cindex Profiling In order to profile a program the first step is to tell the compiler to generate the necessary profiling information. The compiler switch to be used is @code{-pg}, which must be added to other compilation switches. This switch needs to be specified both during compilation and link stages, and can be specified once when using gnatmake: @smallexample gnatmake -f -pg -P my_project @end smallexample @noindent Note that only the objects that were compiled with the @samp{-pg} switch will be profiled; if you need to profile your whole project, use the @samp{-f} gnatmake switch to force full recompilation. @node Program execution @subsection Program execution @noindent Once the program has been compiled for profiling, you can run it as usual. The only constraint imposed by profiling is that the program must terminate normally. An interrupted program (via a Ctrl-C, kill, etc.) will not be properly analyzed. Once the program completes execution, a data file called @file{gmon.out} is generated in the directory where the program was launched from. If this file already exists, it will be overwritten. @node Running gprof @subsection Running gprof @noindent The @code{gprof} tool is called as follow: @smallexample gprof my_prog gmon.out @end smallexample @noindent or simpler: @smallexample gprof my_prog @end smallexample @noindent The complete form of the gprof command line is the following: @smallexample gprof [^switches^options^] [executable [data-file]] @end smallexample @noindent @code{gprof} supports numerous ^switch^options^. The order of these ^switch^options^ does not matter. The full list of options can be found in the GNU Profiler User's Guide documentation that comes with this documentation. The following is the subset of those switches that is most relevant: @table @option @item --demangle[=@var{style}] @itemx --no-demangle @cindex @option{--demangle} (@code{gprof}) These options control whether symbol names should be demangled when printing output. The default is to demangle C++ symbols. The @code{--no-demangle} option may be used to turn off demangling. Different compilers have different mangling styles. The optional demangling style argument can be used to choose an appropriate demangling style for your compiler, in particular Ada symbols generated by GNAT can be demangled using @code{--demangle=gnat}. @item -e @var{function_name} @cindex @option{-e} (@code{gprof}) The @samp{-e @var{function}} option tells @code{gprof} not to print information about the function @var{function_name} (and its children@dots{}) in the call graph. The function will still be listed as a child of any functions that call it, but its index number will be shown as @samp{[not printed]}. More than one @samp{-e} option may be given; only one @var{function_name} may be indicated with each @samp{-e} option. @item -E @var{function_name} @cindex @option{-E} (@code{gprof}) The @code{-E @var{function}} option works like the @code{-e} option, but execution time spent in the function (and children who were not called from anywhere else), will not be used to compute the percentages-of-time for the call graph. More than one @samp{-E} option may be given; only one @var{function_name} may be indicated with each @samp{-E} option. @item -f @var{function_name} @cindex @option{-f} (@code{gprof}) The @samp{-f @var{function}} option causes @code{gprof} to limit the call graph to the function @var{function_name} and its children (and their children@dots{}). More than one @samp{-f} option may be given; only one @var{function_name} may be indicated with each @samp{-f} option. @item -F @var{function_name} @cindex @option{-F} (@code{gprof}) The @samp{-F @var{function}} option works like the @code{-f} option, but only time spent in the function and its children (and their children@dots{}) will be used to determine total-time and percentages-of-time for the call graph. More than one @samp{-F} option may be given; only one @var{function_name} may be indicated with each @samp{-F} option. The @samp{-F} option overrides the @samp{-E} option. @end table @node Interpretation of profiling results @subsection Interpretation of profiling results @noindent The results of the profiling analysis are represented by two arrays: the 'flat profile' and the 'call graph'. Full documentation of those outputs can be found in the GNU Profiler User's Guide. The flat profile shows the time spent in each function of the program, and how many time it has been called. This allows you to locate easily the most time-consuming functions. The call graph shows, for each subprogram, the subprograms that call it, and the subprograms that it calls. It also provides an estimate of the time spent in each of those callers/called subprograms. @end ifclear @c ****************************** @node Running and Debugging Ada Programs @chapter Running and Debugging Ada Programs @cindex Debugging @noindent This chapter discusses how to debug Ada programs. @ifset vms It applies to GNAT on the Alpha OpenVMS platform; for I64 OpenVMS please refer to the @cite{OpenVMS Debugger Manual}, since HP has implemented Ada support in the OpenVMS debugger on I64. @end ifset An incorrect Ada program may be handled in three ways by the GNAT compiler: @enumerate @item The illegality may be a violation of the static semantics of Ada. In that case GNAT diagnoses the constructs in the program that are illegal. It is then a straightforward matter for the user to modify those parts of the program. @item The illegality may be a violation of the dynamic semantics of Ada. In that case the program compiles and executes, but may generate incorrect results, or may terminate abnormally with some exception. @item When presented with a program that contains convoluted errors, GNAT itself may terminate abnormally without providing full diagnostics on the incorrect user program. @end enumerate @menu * The GNAT Debugger GDB:: * Running GDB:: * Introduction to GDB Commands:: * Using Ada Expressions:: * Calling User-Defined Subprograms:: * Using the Next Command in a Function:: * Ada Exceptions:: * Ada Tasks:: * Debugging Generic Units:: * Remote Debugging using gdbserver:: * GNAT Abnormal Termination or Failure to Terminate:: * Naming Conventions for GNAT Source Files:: * Getting Internal Debugging Information:: * Stack Traceback:: @end menu @cindex Debugger @findex gdb @node The GNAT Debugger GDB @section The GNAT Debugger GDB @noindent @code{GDB} is a general purpose, platform-independent debugger that can be used to debug mixed-language programs compiled with @command{gcc}, and in particular is capable of debugging Ada programs compiled with GNAT. The latest versions of @code{GDB} are Ada-aware and can handle complex Ada data structures. @xref{Top,, Debugging with GDB, gdb, Debugging with GDB}, @ifset vms located in the GNU:[DOCS] directory, @end ifset for full details on the usage of @code{GDB}, including a section on its usage on programs. This manual should be consulted for full details. The section that follows is a brief introduction to the philosophy and use of @code{GDB}. When GNAT programs are compiled, the compiler optionally writes debugging information into the generated object file, including information on line numbers, and on declared types and variables. This information is separate from the generated code. It makes the object files considerably larger, but it does not add to the size of the actual executable that will be loaded into memory, and has no impact on run-time performance. The generation of debug information is triggered by the use of the ^-g^/DEBUG^ switch in the @command{gcc} or @command{gnatmake} command used to carry out the compilations. It is important to emphasize that the use of these options does not change the generated code. The debugging information is written in standard system formats that are used by many tools, including debuggers and profilers. The format of the information is typically designed to describe C types and semantics, but GNAT implements a translation scheme which allows full details about Ada types and variables to be encoded into these standard C formats. Details of this encoding scheme may be found in the file exp_dbug.ads in the GNAT source distribution. However, the details of this encoding are, in general, of no interest to a user, since @code{GDB} automatically performs the necessary decoding. When a program is bound and linked, the debugging information is collected from the object files, and stored in the executable image of the program. Again, this process significantly increases the size of the generated executable file, but it does not increase the size of the executable program itself. Furthermore, if this program is run in the normal manner, it runs exactly as if the debug information were not present, and takes no more actual memory. However, if the program is run under control of @code{GDB}, the debugger is activated. The image of the program is loaded, at which point it is ready to run. If a run command is given, then the program will run exactly as it would have if @code{GDB} were not present. This is a crucial part of the @code{GDB} design philosophy. @code{GDB} is entirely non-intrusive until a breakpoint is encountered. If no breakpoint is ever hit, the program will run exactly as it would if no debugger were present. When a breakpoint is hit, @code{GDB} accesses the debugging information and can respond to user commands to inspect variables, and more generally to report on the state of execution. @c ************** @node Running GDB @section Running GDB @noindent This section describes how to initiate the debugger. @c The above sentence is really just filler, but it was otherwise @c clumsy to get the first paragraph nonindented given the conditional @c nature of the description @ifclear vms The debugger can be launched from a @code{GPS} menu or directly from the command line. The description below covers the latter use. All the commands shown can be used in the @code{GPS} debug console window, but there are usually more GUI-based ways to achieve the same effect. @end ifclear The command to run @code{GDB} is @smallexample $ ^gdb program^GDB PROGRAM^ @end smallexample @noindent where @code{^program^PROGRAM^} is the name of the executable file. This activates the debugger and results in a prompt for debugger commands. The simplest command is simply @code{run}, which causes the program to run exactly as if the debugger were not present. The following section describes some of the additional commands that can be given to @code{GDB}. @c ******************************* @node Introduction to GDB Commands @section Introduction to GDB Commands @noindent @code{GDB} contains a large repertoire of commands. @xref{Top,, Debugging with GDB, gdb, Debugging with GDB}, @ifset vms located in the GNU:[DOCS] directory, @end ifset for extensive documentation on the use of these commands, together with examples of their use. Furthermore, the command @command{help} invoked from within GDB activates a simple help facility which summarizes the available commands and their options. In this section we summarize a few of the most commonly used commands to give an idea of what @code{GDB} is about. You should create a simple program with debugging information and experiment with the use of these @code{GDB} commands on the program as you read through the following section. @table @code @item set args @var{arguments} The @var{arguments} list above is a list of arguments to be passed to the program on a subsequent run command, just as though the arguments had been entered on a normal invocation of the program. The @code{set args} command is not needed if the program does not require arguments. @item run The @code{run} command causes execution of the program to start from the beginning. If the program is already running, that is to say if you are currently positioned at a breakpoint, then a prompt will ask for confirmation that you want to abandon the current execution and restart. @item breakpoint @var{location} The breakpoint command sets a breakpoint, that is to say a point at which execution will halt and @code{GDB} will await further commands. @var{location} is either a line number within a file, given in the format @code{file:linenumber}, or it is the name of a subprogram. If you request that a breakpoint be set on a subprogram that is overloaded, a prompt will ask you to specify on which of those subprograms you want to breakpoint. You can also specify that all of them should be breakpointed. If the program is run and execution encounters the breakpoint, then the program stops and @code{GDB} signals that the breakpoint was encountered by printing the line of code before which the program is halted. @item catch exception @var{name} This command causes the program execution to stop whenever exception @var{name} is raised. If @var{name} is omitted, then the execution is suspended when any exception is raised. @item print @var{expression} This will print the value of the given expression. Most simple Ada expression formats are properly handled by @code{GDB}, so the expression can contain function calls, variables, operators, and attribute references. @item continue Continues execution following a breakpoint, until the next breakpoint or the termination of the program. @item step Executes a single line after a breakpoint. If the next statement is a subprogram call, execution continues into (the first statement of) the called subprogram. @item next Executes a single line. If this line is a subprogram call, executes and returns from the call. @item list Lists a few lines around the current source location. In practice, it is usually more convenient to have a separate edit window open with the relevant source file displayed. Successive applications of this command print subsequent lines. The command can be given an argument which is a line number, in which case it displays a few lines around the specified one. @item backtrace Displays a backtrace of the call chain. This command is typically used after a breakpoint has occurred, to examine the sequence of calls that leads to the current breakpoint. The display includes one line for each activation record (frame) corresponding to an active subprogram. @item up At a breakpoint, @code{GDB} can display the values of variables local to the current frame. The command @code{up} can be used to examine the contents of other active frames, by moving the focus up the stack, that is to say from callee to caller, one frame at a time. @item down Moves the focus of @code{GDB} down from the frame currently being examined to the frame of its callee (the reverse of the previous command), @item frame @var{n} Inspect the frame with the given number. The value 0 denotes the frame of the current breakpoint, that is to say the top of the call stack. @end table @noindent The above list is a very short introduction to the commands that @code{GDB} provides. Important additional capabilities, including conditional breakpoints, the ability to execute command sequences on a breakpoint, the ability to debug at the machine instruction level and many other features are described in detail in @ref{Top,, Debugging with GDB, gdb, Debugging with GDB}. Note that most commands can be abbreviated (for example, c for continue, bt for backtrace). @node Using Ada Expressions @section Using Ada Expressions @cindex Ada expressions @noindent @code{GDB} supports a fairly large subset of Ada expression syntax, with some extensions. The philosophy behind the design of this subset is @itemize @bullet @item That @code{GDB} should provide basic literals and access to operations for arithmetic, dereferencing, field selection, indexing, and subprogram calls, leaving more sophisticated computations to subprograms written into the program (which therefore may be called from @code{GDB}). @item That type safety and strict adherence to Ada language restrictions are not particularly important to the @code{GDB} user. @item That brevity is important to the @code{GDB} user. @end itemize @noindent Thus, for brevity, the debugger acts as if there were implicit @code{with} and @code{use} clauses in effect for all user-written packages, thus making it unnecessary to fully qualify most names with their packages, regardless of context. Where this causes ambiguity, @code{GDB} asks the user's intent. For details on the supported Ada syntax, see @ref{Top,, Debugging with GDB, gdb, Debugging with GDB}. @node Calling User-Defined Subprograms @section Calling User-Defined Subprograms @noindent An important capability of @code{GDB} is the ability to call user-defined subprograms while debugging. This is achieved simply by entering a subprogram call statement in the form: @smallexample call subprogram-name (parameters) @end smallexample @noindent The keyword @code{call} can be omitted in the normal case where the @code{subprogram-name} does not coincide with any of the predefined @code{GDB} commands. The effect is to invoke the given subprogram, passing it the list of parameters that is supplied. The parameters can be expressions and can include variables from the program being debugged. The subprogram must be defined at the library level within your program, and @code{GDB} will call the subprogram within the environment of your program execution (which means that the subprogram is free to access or even modify variables within your program). The most important use of this facility is in allowing the inclusion of debugging routines that are tailored to particular data structures in your program. Such debugging routines can be written to provide a suitably high-level description of an abstract type, rather than a low-level dump of its physical layout. After all, the standard @code{GDB print} command only knows the physical layout of your types, not their abstract meaning. Debugging routines can provide information at the desired semantic level and are thus enormously useful. For example, when debugging GNAT itself, it is crucial to have access to the contents of the tree nodes used to represent the program internally. But tree nodes are represented simply by an integer value (which in turn is an index into a table of nodes). Using the @code{print} command on a tree node would simply print this integer value, which is not very useful. But the PN routine (defined in file treepr.adb in the GNAT sources) takes a tree node as input, and displays a useful high level representation of the tree node, which includes the syntactic category of the node, its position in the source, the integers that denote descendant nodes and parent node, as well as varied semantic information. To study this example in more detail, you might want to look at the body of the PN procedure in the stated file. @node Using the Next Command in a Function @section Using the Next Command in a Function @noindent When you use the @code{next} command in a function, the current source location will advance to the next statement as usual. A special case arises in the case of a @code{return} statement. Part of the code for a return statement is the ``epilog'' of the function. This is the code that returns to the caller. There is only one copy of this epilog code, and it is typically associated with the last return statement in the function if there is more than one return. In some implementations, this epilog is associated with the first statement of the function. The result is that if you use the @code{next} command from a return statement that is not the last return statement of the function you may see a strange apparent jump to the last return statement or to the start of the function. You should simply ignore this odd jump. The value returned is always that from the first return statement that was stepped through. @node Ada Exceptions @section Stopping when Ada Exceptions are Raised @cindex Exceptions @noindent You can set catchpoints that stop the program execution when your program raises selected exceptions. @table @code @item catch exception Set a catchpoint that stops execution whenever (any task in the) program raises any exception. @item catch exception @var{name} Set a catchpoint that stops execution whenever (any task in the) program raises the exception @var{name}. @item catch exception unhandled Set a catchpoint that stops executino whenever (any task in the) program raises an exception for which there is no handler. @item info exceptions @itemx info exceptions @var{regexp} The @code{info exceptions} command permits the user to examine all defined exceptions within Ada programs. With a regular expression, @var{regexp}, as argument, prints out only those exceptions whose name matches @var{regexp}. @end table @node Ada Tasks @section Ada Tasks @cindex Tasks @noindent @code{GDB} allows the following task-related commands: @table @code @item info tasks This command shows a list of current Ada tasks, as in the following example: @smallexample @iftex @leftskip=0cm @end iftex (gdb) info tasks ID TID P-ID Thread Pri State Name 1 8088000 0 807e000 15 Child Activation Wait main_task 2 80a4000 1 80ae000 15 Accept/Select Wait b 3 809a800 1 80a4800 15 Child Activation Wait a * 4 80ae800 3 80b8000 15 Running c @end smallexample @noindent In this listing, the asterisk before the first task indicates it to be the currently running task. The first column lists the task ID that is used to refer to tasks in the following commands. @item break @var{linespec} task @var{taskid} @itemx break @var{linespec} task @var{taskid} if @dots{} @cindex Breakpoints and tasks These commands are like the @code{break @dots{} thread @dots{}}. @var{linespec} specifies source lines. Use the qualifier @samp{task @var{taskid}} with a breakpoint command to specify that you only want @code{GDB} to stop the program when a particular Ada task reaches this breakpoint. @var{taskid} is one of the numeric task identifiers assigned by @code{GDB}, shown in the first column of the @samp{info tasks} display. If you do not specify @samp{task @var{taskid}} when you set a breakpoint, the breakpoint applies to @emph{all} tasks of your program. You can use the @code{task} qualifier on conditional breakpoints as well; in this case, place @samp{task @var{taskid}} before the breakpoint condition (before the @code{if}). @item task @var{taskno} @cindex Task switching This command allows to switch to the task referred by @var{taskno}. In particular, This allows to browse the backtrace of the specified task. It is advised to switch back to the original task before continuing execution otherwise the scheduling of the program may be perturbed. @end table @noindent For more detailed information on the tasking support, see @ref{Top,, Debugging with GDB, gdb, Debugging with GDB}. @node Debugging Generic Units @section Debugging Generic Units @cindex Debugging Generic Units @cindex Generics @noindent GNAT always uses code expansion for generic instantiation. This means that each time an instantiation occurs, a complete copy of the original code is made, with appropriate substitutions of formals by actuals. It is not possible to refer to the original generic entities in @code{GDB}, but it is always possible to debug a particular instance of a generic, by using the appropriate expanded names. For example, if we have @smallexample @c ada @group @cartouche procedure g is generic package k is procedure kp (v1 : in out integer); end k; package body k is procedure kp (v1 : in out integer) is begin v1 := v1 + 1; end kp; end k; package k1 is new k; package k2 is new k; var : integer := 1; begin k1.kp (var); k2.kp (var); k1.kp (var); k2.kp (var); end; @end cartouche @end group @end smallexample @noindent Then to break on a call to procedure kp in the k2 instance, simply use the command: @smallexample (gdb) break g.k2.kp @end smallexample @noindent When the breakpoint occurs, you can step through the code of the instance in the normal manner and examine the values of local variables, as for other units. @node Remote Debugging using gdbserver @section Remote Debugging using gdbserver @cindex Remote Debugging using gdbserver @noindent On platforms where gdbserver is supported, it is possible to use this tool to debug your application remotely. This can be useful in situations where the program needs to be run on a target host that is different from the host used for development, particularly when the target has a limited amount of resources (either CPU and/or memory). To do so, start your program using gdbserver on the target machine. gdbserver then automatically suspends the execution of your program at its entry point, waiting for a debugger to connect to it. The following commands starts an application and tells gdbserver to wait for a connection with the debugger on localhost port 4444. @smallexample $ gdbserver localhost:4444 program Process program created; pid = 5685 Listening on port 4444 @end smallexample Once gdbserver has started listening, we can tell the debugger to establish a connection with this gdbserver, and then start the same debugging session as if the program was being debugged on the same host, directly under the control of GDB. @smallexample $ gdb program (gdb) target remote targethost:4444 Remote debugging using targethost:4444 0x00007f29936d0af0 in ?? () from /lib64/ld-linux-x86-64.so. (gdb) b foo.adb:3 Breakpoint 1 at 0x401f0c: file foo.adb, line 3. (gdb) continue Continuing. Breakpoint 1, foo () at foo.adb:4 4 end foo; @end smallexample It is also possible to use gdbserver to attach to an already running program, in which case the execution of that program is simply suspended until the connection between the debugger and gdbserver is established. For more information on how to use gdbserver, @ref{Top, Server, Using the gdbserver Program, gdb, Debugging with GDB}. GNAT Pro provides support for gdbserver on x86-linux, x86-windows and x86_64-linux. @node GNAT Abnormal Termination or Failure to Terminate @section GNAT Abnormal Termination or Failure to Terminate @cindex GNAT Abnormal Termination or Failure to Terminate @noindent When presented with programs that contain serious errors in syntax or semantics, GNAT may on rare occasions experience problems in operation, such as aborting with a segmentation fault or illegal memory access, raising an internal exception, terminating abnormally, or failing to terminate at all. In such cases, you can activate various features of GNAT that can help you pinpoint the construct in your program that is the likely source of the problem. The following strategies are presented in increasing order of difficulty, corresponding to your experience in using GNAT and your familiarity with compiler internals. @enumerate @item Run @command{gcc} with the @option{-gnatf}. This first switch causes all errors on a given line to be reported. In its absence, only the first error on a line is displayed. The @option{-gnatdO} switch causes errors to be displayed as soon as they are encountered, rather than after compilation is terminated. If GNAT terminates prematurely or goes into an infinite loop, the last error message displayed may help to pinpoint the culprit. @item Run @command{gcc} with the @option{^-v (verbose)^/VERBOSE^} switch. In this mode, @command{gcc} produces ongoing information about the progress of the compilation and provides the name of each procedure as code is generated. This switch allows you to find which Ada procedure was being compiled when it encountered a code generation problem. @item @cindex @option{-gnatdc} switch Run @command{gcc} with the @option{-gnatdc} switch. This is a GNAT specific switch that does for the front-end what @option{^-v^VERBOSE^} does for the back end. The system prints the name of each unit, either a compilation unit or nested unit, as it is being analyzed. @item Finally, you can start @code{gdb} directly on the @code{gnat1} executable. @code{gnat1} is the front-end of GNAT, and can be run independently (normally it is just called from @command{gcc}). You can use @code{gdb} on @code{gnat1} as you would on a C program (but @pxref{The GNAT Debugger GDB} for caveats). The @code{where} command is the first line of attack; the variable @code{lineno} (seen by @code{print lineno}), used by the second phase of @code{gnat1} and by the @command{gcc} backend, indicates the source line at which the execution stopped, and @code{input_file name} indicates the name of the source file. @end enumerate @node Naming Conventions for GNAT Source Files @section Naming Conventions for GNAT Source Files @noindent In order to examine the workings of the GNAT system, the following brief description of its organization may be helpful: @itemize @bullet @item Files with prefix @file{^sc^SC^} contain the lexical scanner. @item All files prefixed with @file{^par^PAR^} are components of the parser. The numbers correspond to chapters of the Ada Reference Manual. For example, parsing of select statements can be found in @file{par-ch9.adb}. @item All files prefixed with @file{^sem^SEM^} perform semantic analysis. The numbers correspond to chapters of the Ada standard. For example, all issues involving context clauses can be found in @file{sem_ch10.adb}. In addition, some features of the language require sufficient special processing to justify their own semantic files: sem_aggr for aggregates, sem_disp for dynamic dispatching, etc. @item All files prefixed with @file{^exp^EXP^} perform normalization and expansion of the intermediate representation (abstract syntax tree, or AST). these files use the same numbering scheme as the parser and semantics files. For example, the construction of record initialization procedures is done in @file{exp_ch3.adb}. @item The files prefixed with @file{^bind^BIND^} implement the binder, which verifies the consistency of the compilation, determines an order of elaboration, and generates the bind file. @item The files @file{atree.ads} and @file{atree.adb} detail the low-level data structures used by the front-end. @item The files @file{sinfo.ads} and @file{sinfo.adb} detail the structure of the abstract syntax tree as produced by the parser. @item The files @file{einfo.ads} and @file{einfo.adb} detail the attributes of all entities, computed during semantic analysis. @item Library management issues are dealt with in files with prefix @file{^lib^LIB^}. @item @findex Ada @cindex Annex A Ada files with the prefix @file{^a-^A-^} are children of @code{Ada}, as defined in Annex A. @item @findex Interfaces @cindex Annex B Files with prefix @file{^i-^I-^} are children of @code{Interfaces}, as defined in Annex B. @item @findex System Files with prefix @file{^s-^S-^} are children of @code{System}. This includes both language-defined children and GNAT run-time routines. @item @findex GNAT Files with prefix @file{^g-^G-^} are children of @code{GNAT}. These are useful general-purpose packages, fully documented in their specs. All the other @file{.c} files are modifications of common @command{gcc} files. @end itemize @node Getting Internal Debugging Information @section Getting Internal Debugging Information @noindent Most compilers have internal debugging switches and modes. GNAT does also, except GNAT internal debugging switches and modes are not secret. A summary and full description of all the compiler and binder debug flags are in the file @file{debug.adb}. You must obtain the sources of the compiler to see the full detailed effects of these flags. The switches that print the source of the program (reconstructed from the internal tree) are of general interest for user programs, as are the options to print the full internal tree, and the entity table (the symbol table information). The reconstructed source provides a readable version of the program after the front-end has completed analysis and expansion, and is useful when studying the performance of specific constructs. For example, constraint checks are indicated, complex aggregates are replaced with loops and assignments, and tasking primitives are replaced with run-time calls. @node Stack Traceback @section Stack Traceback @cindex traceback @cindex stack traceback @cindex stack unwinding @noindent Traceback is a mechanism to display the sequence of subprogram calls that leads to a specified execution point in a program. Often (but not always) the execution point is an instruction at which an exception has been raised. This mechanism is also known as @i{stack unwinding} because it obtains its information by scanning the run-time stack and recovering the activation records of all active subprograms. Stack unwinding is one of the most important tools for program debugging. The first entry stored in traceback corresponds to the deepest calling level, that is to say the subprogram currently executing the instruction from which we want to obtain the traceback. Note that there is no runtime performance penalty when stack traceback is enabled, and no exception is raised during program execution. @menu * Non-Symbolic Traceback:: * Symbolic Traceback:: @end menu @node Non-Symbolic Traceback @subsection Non-Symbolic Traceback @cindex traceback, non-symbolic @noindent Note: this feature is not supported on all platforms. See @file{GNAT.Traceback spec in g-traceb.ads} for a complete list of supported platforms. @menu * Tracebacks From an Unhandled Exception:: * Tracebacks From Exception Occurrences (non-symbolic):: * Tracebacks From Anywhere in a Program (non-symbolic):: @end menu @node Tracebacks From an Unhandled Exception @subsubsection Tracebacks From an Unhandled Exception @noindent A runtime non-symbolic traceback is a list of addresses of call instructions. To enable this feature you must use the @option{-E} @code{gnatbind}'s option. With this option a stack traceback is stored as part of exception information. You can retrieve this information using the @code{addr2line} tool. Here is a simple example: @smallexample @c ada @cartouche procedure STB is procedure P1 is begin raise Constraint_Error; end P1; procedure P2 is begin P1; end P2; begin P2; end STB; @end cartouche @end smallexample @smallexample $ gnatmake stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 @end smallexample @noindent As we see the traceback lists a sequence of addresses for the unhandled exception @code{CONSTRAINT_ERROR} raised in procedure P1. It is easy to guess that this exception come from procedure P1. To translate these addresses into the source lines where the calls appear, the @code{addr2line} tool, described below, is invaluable. The use of this tool requires the program to be compiled with debug information. @smallexample $ gnatmake -g stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 $ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 00401373 at d:/stb/stb.adb:5 0040138B at d:/stb/stb.adb:10 0040139C at d:/stb/stb.adb:14 00401335 at d:/stb/b~stb.adb:104 004011C4 at /build/@dots{}/crt1.c:200 004011F1 at /build/@dots{}/crt1.c:222 77E892A4 in ?? at ??:0 @end smallexample @noindent The @code{addr2line} tool has several other useful options: @table @code @item --functions to get the function name corresponding to any location @item --demangle=gnat to use the gnat decoding mode for the function names. Note that for binutils version 2.9.x the option is simply @option{--demangle}. @end table @smallexample $ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 00401373 in stb.p1 at d:/stb/stb.adb:5 0040138B in stb.p2 at d:/stb/stb.adb:10 0040139C in stb at d:/stb/stb.adb:14 00401335 in main at d:/stb/b~stb.adb:104 004011C4 in <__mingw_CRTStartup> at /build/@dots{}/crt1.c:200 004011F1 in at /build/@dots{}/crt1.c:222 @end smallexample @noindent From this traceback we can see that the exception was raised in @file{stb.adb} at line 5, which was reached from a procedure call in @file{stb.adb} at line 10, and so on. The @file{b~std.adb} is the binder file, which contains the call to the main program. @xref{Running gnatbind}. The remaining entries are assorted runtime routines, and the output will vary from platform to platform. It is also possible to use @code{GDB} with these traceback addresses to debug the program. For example, we can break at a given code location, as reported in the stack traceback: @smallexample $ gdb -nw stb @ifclear vms @noindent Furthermore, this feature is not implemented inside Windows DLL. Only the non-symbolic traceback is reported in this case. @end ifclear (gdb) break *0x401373 Breakpoint 1 at 0x401373: file stb.adb, line 5. @end smallexample @noindent It is important to note that the stack traceback addresses do not change when debug information is included. This is particularly useful because it makes it possible to release software without debug information (to minimize object size), get a field report that includes a stack traceback whenever an internal bug occurs, and then be able to retrieve the sequence of calls with the same program compiled with debug information. @node Tracebacks From Exception Occurrences (non-symbolic) @subsubsection Tracebacks From Exception Occurrences @noindent Non-symbolic tracebacks are obtained by using the @option{-E} binder argument. The stack traceback is attached to the exception information string, and can be retrieved in an exception handler within the Ada program, by means of the Ada facilities defined in @code{Ada.Exceptions}. Here is a simple example: @smallexample @c ada with Ada.Text_IO; with Ada.Exceptions; procedure STB is use Ada; use Ada.Exceptions; procedure P1 is K : Positive := 1; begin K := K - 1; exception when E : others => Text_IO.Put_Line (Exception_Information (E)); end P1; procedure P2 is begin P1; end P2; begin P2; end STB; @end smallexample @noindent This program will output: @smallexample $ stb Exception name: CONSTRAINT_ERROR Message: stb.adb:12 Call stack traceback locations: 0x4015e4 0x401633 0x401644 0x401461 0x4011c4 0x4011f1 0x77e892a4 @end smallexample @node Tracebacks From Anywhere in a Program (non-symbolic) @subsubsection Tracebacks From Anywhere in a Program @noindent It is also possible to retrieve a stack traceback from anywhere in a program. For this you need to use the @code{GNAT.Traceback} API. This package includes a procedure called @code{Call_Chain} that computes a complete stack traceback, as well as useful display procedures described below. It is not necessary to use the @option{-E gnatbind} option in this case, because the stack traceback mechanism is invoked explicitly. @noindent In the following example we compute a traceback at a specific location in the program, and we display it using @code{GNAT.Debug_Utilities.Image} to convert addresses to strings: @smallexample @c ada with Ada.Text_IO; with GNAT.Traceback; with GNAT.Debug_Utilities; procedure STB is use Ada; use GNAT; use GNAT.Traceback; procedure P1 is TB : Tracebacks_Array (1 .. 10); -- We are asking for a maximum of 10 stack frames. Len : Natural; -- Len will receive the actual number of stack frames returned. begin Call_Chain (TB, Len); Text_IO.Put ("In STB.P1 : "); for K in 1 .. Len loop Text_IO.Put (Debug_Utilities.Image (TB (K))); Text_IO.Put (' '); end loop; Text_IO.New_Line; end P1; procedure P2 is begin P1; end P2; begin P2; end STB; @end smallexample @smallexample $ gnatmake -g stb $ stb In STB.P1 : 16#0040_F1E4# 16#0040_14F2# 16#0040_170B# 16#0040_171C# 16#0040_1461# 16#0040_11C4# 16#0040_11F1# 16#77E8_92A4# @end smallexample @noindent You can then get further information by invoking the @code{addr2line} tool as described earlier (note that the hexadecimal addresses need to be specified in C format, with a leading ``0x''). @node Symbolic Traceback @subsection Symbolic Traceback @cindex traceback, symbolic @noindent A symbolic traceback is a stack traceback in which procedure names are associated with each code location. @noindent Note that this feature is not supported on all platforms. See @file{GNAT.Traceback.Symbolic spec in g-trasym.ads} for a complete list of currently supported platforms. @noindent Note that the symbolic traceback requires that the program be compiled with debug information. If it is not compiled with debug information only the non-symbolic information will be valid. @menu * Tracebacks From Exception Occurrences (symbolic):: * Tracebacks From Anywhere in a Program (symbolic):: @end menu @node Tracebacks From Exception Occurrences (symbolic) @subsubsection Tracebacks From Exception Occurrences @smallexample @c ada with Ada.Text_IO; with GNAT.Traceback.Symbolic; procedure STB is procedure P1 is begin raise Constraint_Error; end P1; procedure P2 is begin P1; end P2; procedure P3 is begin P2; end P3; begin P3; exception when E : others => Ada.Text_IO.Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (E)); end STB; @end smallexample @smallexample $ gnatmake -g .\stb -bargs -E -largs -lgnat -laddr2line -lintl $ stb 0040149F in stb.p1 at stb.adb:8 004014B7 in stb.p2 at stb.adb:13 004014CF in stb.p3 at stb.adb:18 004015DD in ada.stb at stb.adb:22 00401461 in main at b~stb.adb:168 004011C4 in __mingw_CRTStartup at crt1.c:200 004011F1 in mainCRTStartup at crt1.c:222 77E892A4 in ?? at ??:0 @end smallexample @noindent In the above example the ``.\'' syntax in the @command{gnatmake} command is currently required by @command{addr2line} for files that are in the current working directory. Moreover, the exact sequence of linker options may vary from platform to platform. The above @option{-largs} section is for Windows platforms. By contrast, under Unix there is no need for the @option{-largs} section. Differences across platforms are due to details of linker implementation. @node Tracebacks From Anywhere in a Program (symbolic) @subsubsection Tracebacks From Anywhere in a Program @noindent It is possible to get a symbolic stack traceback from anywhere in a program, just as for non-symbolic tracebacks. The first step is to obtain a non-symbolic traceback, and then call @code{Symbolic_Traceback} to compute the symbolic information. Here is an example: @smallexample @c ada with Ada.Text_IO; with GNAT.Traceback; with GNAT.Traceback.Symbolic; procedure STB is use Ada; use GNAT.Traceback; use GNAT.Traceback.Symbolic; procedure P1 is TB : Tracebacks_Array (1 .. 10); -- We are asking for a maximum of 10 stack frames. Len : Natural; -- Len will receive the actual number of stack frames returned. begin Call_Chain (TB, Len); Text_IO.Put_Line (Symbolic_Traceback (TB (1 .. Len))); end P1; procedure P2 is begin P1; end P2; begin P2; end STB; @end smallexample @c ****************************** @ifset vms @node Compatibility with HP Ada @chapter Compatibility with HP Ada @cindex Compatibility @noindent @cindex DEC Ada @cindex HP Ada @cindex Compatibility between GNAT and HP Ada This chapter compares HP Ada (formerly known as ``DEC Ada'') for OpenVMS Alpha and GNAT for OpenVMS for Alpha and for I64. GNAT is highly compatible with HP Ada, and it should generally be straightforward to port code from the HP Ada environment to GNAT. However, there are a few language and implementation differences of which the user must be aware. These differences are discussed in this chapter. In addition, the operating environment and command structure for the compiler are different, and these differences are also discussed. For further details on these and other compatibility issues, see Appendix E of the HP publication @cite{HP Ada, Technical Overview and Comparison on HP Platforms}. Except where otherwise indicated, the description of GNAT for OpenVMS applies to both the Alpha and I64 platforms. For information on porting Ada code from GNAT on Alpha OpenVMS to GNAT on I64 OpenVMS, see @ref{Transitioning to 64-Bit GNAT for OpenVMS}. The discussion in this chapter addresses specifically the implementation of Ada 83 for HP OpenVMS Alpha Systems. In cases where the implementation of HP Ada differs between OpenVMS Alpha Systems and OpenVMS VAX Systems, GNAT always follows the Alpha implementation. For GNAT running on other than VMS systems, all the HP Ada 83 pragmas and attributes are recognized, although only a subset of them can sensibly be implemented. The description of pragmas in @xref{Implementation Defined Pragmas,,, gnat_rm, GNAT Reference Manual}, indicates whether or not they are applicable to non-VMS systems. @menu * Ada Language Compatibility:: * Differences in the Definition of Package System:: * Language-Related Features:: * The Package STANDARD:: * The Package SYSTEM:: * Tasking and Task-Related Features:: * Pragmas and Pragma-Related Features:: * Library of Predefined Units:: * Bindings:: * Main Program Definition:: * Implementation-Defined Attributes:: * Compiler and Run-Time Interfacing:: * Program Compilation and Library Management:: * Input-Output:: * Implementation Limits:: * Tools and Utilities:: @end menu @node Ada Language Compatibility @section Ada Language Compatibility @noindent GNAT handles Ada 95 and Ada 2005 as well as Ada 83, whereas HP Ada is only for Ada 83. Ada 95 and Ada 2005 are almost completely upwards compatible with Ada 83, and therefore Ada 83 programs will compile and run under GNAT with no changes or only minor changes. The @cite{Annotated Ada Reference Manual} provides details on specific incompatibilities. GNAT provides the switch @option{/83} on the @command{GNAT COMPILE} command, as well as the pragma @code{ADA_83}, to force the compiler to operate in Ada 83 mode. This mode does not guarantee complete conformance to Ada 83, but in practice is sufficient to eliminate most sources of incompatibilities. In particular, it eliminates the recognition of the additional Ada 95 and Ada 2005 keywords, so that their use as identifiers in Ada 83 programs is legal, and handles the cases of packages with optional bodies, and generics that instantiate unconstrained types without the use of @code{(<>)}. @node Differences in the Definition of Package System @section Differences in the Definition of Package @code{System} @noindent An Ada compiler is allowed to add implementation-dependent declarations to package @code{System}. In normal mode, GNAT does not take advantage of this permission, and the version of @code{System} provided by GNAT exactly matches that defined in the Ada Reference Manual. However, HP Ada adds an extensive set of declarations to package @code{System}, as fully documented in the HP Ada manuals. To minimize changes required for programs that make use of these extensions, GNAT provides the pragma @code{Extend_System} for extending the definition of package System. By using: @cindex pragma @code{Extend_System} @cindex @code{Extend_System} pragma @smallexample @c ada @group @cartouche pragma Extend_System (Aux_DEC); @end cartouche @end group @end smallexample @noindent the set of definitions in @code{System} is extended to include those in package @code{System.Aux_DEC}. @cindex @code{System.Aux_DEC} package @cindex @code{Aux_DEC} package (child of @code{System}) These definitions are incorporated directly into package @code{System}, as though they had been declared there. For a list of the declarations added, see the spec of this package, which can be found in the file @file{s-auxdec.ads} in the GNAT library. @cindex @file{s-auxdec.ads} file The pragma @code{Extend_System} is a configuration pragma, which means that it can be placed in the file @file{gnat.adc}, so that it will automatically apply to all subsequent compilations. See @ref{Configuration Pragmas}, for further details. An alternative approach that avoids the use of the non-standard @code{Extend_System} pragma is to add a context clause to the unit that references these facilities: @smallexample @c ada @cartouche with System.Aux_DEC; use System.Aux_DEC; @end cartouche @end smallexample @noindent The effect is not quite semantically identical to incorporating the declarations directly into package @code{System}, but most programs will not notice a difference unless they use prefix notation (e.g.@: @code{System.Integer_8}) to reference the entities directly in package @code{System}. For units containing such references, the prefixes must either be removed, or the pragma @code{Extend_System} must be used. @node Language-Related Features @section Language-Related Features @noindent The following sections highlight differences in types, representations of types, operations, alignment, and related topics. @menu * Integer Types and Representations:: * Floating-Point Types and Representations:: * Pragmas Float_Representation and Long_Float:: * Fixed-Point Types and Representations:: * Record and Array Component Alignment:: * Address Clauses:: * Other Representation Clauses:: @end menu @node Integer Types and Representations @subsection Integer Types and Representations @noindent The set of predefined integer types is identical in HP Ada and GNAT. Furthermore the representation of these integer types is also identical, including the capability of size clauses forcing biased representation. In addition, HP Ada for OpenVMS Alpha systems has defined the following additional integer types in package @code{System}: @itemize @bullet @item @code{INTEGER_8} @item @code{INTEGER_16} @item @code{INTEGER_32} @item @code{INTEGER_64} @item @code{LARGEST_INTEGER} @end itemize @noindent In GNAT, the first four of these types may be obtained from the standard Ada package @code{Interfaces}. Alternatively, by use of the pragma @code{Extend_System}, identical declarations can be referenced directly in package @code{System}. On both GNAT and HP Ada, the maximum integer size is 64 bits. @node Floating-Point Types and Representations @subsection Floating-Point Types and Representations @cindex Floating-Point types @noindent The set of predefined floating-point types is identical in HP Ada and GNAT. Furthermore the representation of these floating-point types is also identical. One important difference is that the default representation for HP Ada is @code{VAX_Float}, but the default representation for GNAT is IEEE. Specific types may be declared to be @code{VAX_Float} or IEEE, using the pragma @code{Float_Representation} as described in the HP Ada documentation. For example, the declarations: @smallexample @c ada @cartouche type F_Float is digits 6; pragma Float_Representation (VAX_Float, F_Float); @end cartouche @end smallexample @noindent declares a type @code{F_Float} that will be represented in @code{VAX_Float} format. This set of declarations actually appears in @code{System.Aux_DEC}, which contains the full set of additional floating-point declarations provided in the HP Ada version of package @code{System}. This and similar declarations may be accessed in a user program by using pragma @code{Extend_System}. The use of this pragma, and the related pragma @code{Long_Float} is described in further detail in the following section. @node Pragmas Float_Representation and Long_Float @subsection Pragmas @code{Float_Representation} and @code{Long_Float} @noindent HP Ada provides the pragma @code{Float_Representation}, which acts as a program library switch to allow control over the internal representation chosen for the predefined floating-point types declared in the package @code{Standard}. The format of this pragma is as follows: @smallexample @c ada @cartouche pragma Float_Representation(VAX_Float | IEEE_Float); @end cartouche @end smallexample @noindent This pragma controls the representation of floating-point types as follows: @itemize @bullet @item @code{VAX_Float} specifies that floating-point types are represented by default with the VAX system hardware types @code{F-floating}, @code{D-floating}, @code{G-floating}. Note that the @code{H-floating} type was available only on VAX systems, and is not available in either HP Ada or GNAT. @item @code{IEEE_Float} specifies that floating-point types are represented by default with the IEEE single and double floating-point types. @end itemize @noindent GNAT provides an identical implementation of the pragma @code{Float_Representation}, except that it functions as a configuration pragma. Note that the notion of configuration pragma corresponds closely to the HP Ada notion of a program library switch. When no pragma is used in GNAT, the default is @code{IEEE_Float}, which is different from HP Ada 83, where the default is @code{VAX_Float}. In addition, the predefined libraries in GNAT are built using @code{IEEE_Float}, so it is not advisable to change the format of numbers passed to standard library routines, and if necessary explicit type conversions may be needed. The use of @code{IEEE_Float} is recommended in GNAT since it is more efficient, and (given that it conforms to an international standard) potentially more portable. The situation in which @code{VAX_Float} may be useful is in interfacing to existing code and data that expect the use of @code{VAX_Float}. In such a situation use the predefined @code{VAX_Float} types in package @code{System}, as extended by @code{Extend_System}. For example, use @code{System.F_Float} to specify the 32-bit @code{F-Float} format. @noindent On OpenVMS systems, HP Ada provides the pragma @code{Long_Float} to allow control over the internal representation chosen for the predefined type @code{Long_Float} and for floating-point type declarations with digits specified in the range 7 .. 15. The format of this pragma is as follows: @smallexample @c ada @cartouche pragma Long_Float (D_FLOAT | G_FLOAT); @end cartouche @end smallexample @node Fixed-Point Types and Representations @subsection Fixed-Point Types and Representations @noindent On HP Ada for OpenVMS Alpha systems, rounding is away from zero for both positive and negative numbers. Therefore, @code{+0.5} rounds to @code{1}, and @code{-0.5} rounds to @code{-1}. On GNAT the results of operations on fixed-point types are in accordance with the Ada rules. In particular, results of operations on decimal fixed-point types are truncated. @node Record and Array Component Alignment @subsection Record and Array Component Alignment @noindent On HP Ada for OpenVMS Alpha, all non-composite components are aligned on natural boundaries. For example, 1-byte components are aligned on byte boundaries, 2-byte components on 2-byte boundaries, 4-byte components on 4-byte byte boundaries, and so on. The OpenVMS Alpha hardware runs more efficiently with naturally aligned data. On GNAT, alignment rules are compatible with HP Ada for OpenVMS Alpha. @node Address Clauses @subsection Address Clauses @noindent In HP Ada and GNAT, address clauses are supported for objects and imported subprograms. The predefined type @code{System.Address} is a private type in both compilers on Alpha OpenVMS, with the same representation (it is simply a machine pointer). Addition, subtraction, and comparison operations are available in the standard Ada package @code{System.Storage_Elements}, or in package @code{System} if it is extended to include @code{System.Aux_DEC} using a pragma @code{Extend_System} as previously described. Note that code that @code{with}'s both this extended package @code{System} and the package @code{System.Storage_Elements} should not @code{use} both packages, or ambiguities will result. In general it is better not to mix these two sets of facilities. The Ada package was designed specifically to provide the kind of features that HP Ada adds directly to package @code{System}. The type @code{System.Address} is a 64-bit integer type in GNAT for I64 OpenVMS. For more information, see @ref{Transitioning to 64-Bit GNAT for OpenVMS}. GNAT is compatible with HP Ada in its handling of address clauses, except for some limitations in the form of address clauses for composite objects with initialization. Such address clauses are easily replaced by the use of an explicitly-defined constant as described in the Ada Reference Manual (13.1(22)). For example, the sequence of declarations: @smallexample @c ada @cartouche X, Y : Integer := Init_Func; Q : String (X .. Y) := "abc"; @dots{} for Q'Address use Compute_Address; @end cartouche @end smallexample @noindent will be rejected by GNAT, since the address cannot be computed at the time that @code{Q} is declared. To achieve the intended effect, write instead: @smallexample @c ada @group @cartouche X, Y : Integer := Init_Func; Q_Address : constant Address := Compute_Address; Q : String (X .. Y) := "abc"; @dots{} for Q'Address use Q_Address; @end cartouche @end group @end smallexample @noindent which will be accepted by GNAT (and other Ada compilers), and is also compatible with Ada 83. A fuller description of the restrictions on address specifications is found in @ref{Top, GNAT Reference Manual, About This Guide, gnat_rm, GNAT Reference Manual}. @node Other Representation Clauses @subsection Other Representation Clauses @noindent GNAT implements in a compatible manner all the representation clauses supported by HP Ada. In addition, GNAT implements the representation clause forms that were introduced in Ada 95, including @code{COMPONENT_SIZE} and @code{SIZE} clauses for objects. @node The Package STANDARD @section The Package @code{STANDARD} @noindent The package @code{STANDARD}, as implemented by HP Ada, is fully described in the @cite{Ada Reference Manual} and in the @cite{HP Ada Language Reference Manual}. As implemented by GNAT, the package @code{STANDARD} is described in the @cite{Ada Reference Manual}. In addition, HP Ada supports the Latin-1 character set in the type @code{CHARACTER}. GNAT supports the Latin-1 character set in the type @code{CHARACTER} and also Unicode (ISO 10646 BMP) in the type @code{WIDE_CHARACTER}. The floating-point types supported by GNAT are those supported by HP Ada, but the defaults are different, and are controlled by pragmas. See @ref{Floating-Point Types and Representations}, for details. @node The Package SYSTEM @section The Package @code{SYSTEM} @noindent HP Ada provides a specific version of the package @code{SYSTEM} for each platform on which the language is implemented. For the complete spec of the package @code{SYSTEM}, see Appendix F of the @cite{HP Ada Language Reference Manual}. On HP Ada, the package @code{SYSTEM} includes the following conversion functions: @itemize @bullet @item @code{TO_ADDRESS(INTEGER)} @item @code{TO_ADDRESS(UNSIGNED_LONGWORD)} @item @code{TO_ADDRESS(}@i{universal_integer}@code{)} @item @code{TO_INTEGER(ADDRESS)} @item @code{TO_UNSIGNED_LONGWORD(ADDRESS)} @item Function @code{IMPORT_VALUE return UNSIGNED_LONGWORD} and the functions @code{IMPORT_ADDRESS} and @code{IMPORT_LARGEST_VALUE} @end itemize @noindent By default, GNAT supplies a version of @code{SYSTEM} that matches the definition given in the @cite{Ada Reference Manual}. This is a subset of the HP system definitions, which is as close as possible to the original definitions. The only difference is that the definition of @code{SYSTEM_NAME} is different: @smallexample @c ada @cartouche type Name is (SYSTEM_NAME_GNAT); System_Name : constant Name := SYSTEM_NAME_GNAT; @end cartouche @end smallexample @noindent Also, GNAT adds the Ada declarations for @code{BIT_ORDER} and @code{DEFAULT_BIT_ORDER}. However, the use of the following pragma causes GNAT to extend the definition of package @code{SYSTEM} so that it encompasses the full set of HP-specific extensions, including the functions listed above: @smallexample @c ada @cartouche pragma Extend_System (Aux_DEC); @end cartouche @end smallexample @noindent The pragma @code{Extend_System} is a configuration pragma that is most conveniently placed in the @file{gnat.adc} file. @xref{Pragma Extend_System,,, gnat_rm, GNAT Reference Manual}, for further details. HP Ada does not allow the recompilation of the package @code{SYSTEM}. Instead HP Ada provides several pragmas (@code{SYSTEM_NAME}, @code{STORAGE_UNIT}, and @code{MEMORY_SIZE}) to modify values in the package @code{SYSTEM}. On OpenVMS Alpha systems, the pragma @code{SYSTEM_NAME} takes the enumeration literal @code{OPENVMS_AXP} as its single argument. GNAT does permit the recompilation of package @code{SYSTEM} using the special switch @option{-gnatg}, and this switch can be used if it is necessary to modify the definitions in @code{SYSTEM}. GNAT does not permit the specification of @code{SYSTEM_NAME}, @code{STORAGE_UNIT} or @code{MEMORY_SIZE} by any other means. On GNAT systems, the pragma @code{SYSTEM_NAME} takes the enumeration literal @code{SYSTEM_NAME_GNAT}. The definitions provided by the use of @smallexample @c ada pragma Extend_System (AUX_Dec); @end smallexample @noindent are virtually identical to those provided by the HP Ada 83 package @code{SYSTEM}. One important difference is that the name of the @code{TO_ADDRESS} function for type @code{UNSIGNED_LONGWORD} is changed to @code{TO_ADDRESS_LONG}. @xref{Address Clauses,,, gnat_rm, GNAT Reference Manual}, for a discussion of why this change was necessary. @noindent The version of @code{TO_ADDRESS} taking a @i{universal_integer} argument is in fact an extension to Ada 83 not strictly compatible with the reference manual. GNAT, in order to be exactly compatible with the standard, does not provide this capability. In HP Ada 83, the point of this definition is to deal with a call like: @smallexample @c ada TO_ADDRESS (16#12777#); @end smallexample @noindent Normally, according to Ada 83 semantics, one would expect this to be ambiguous, since it matches both the @code{INTEGER} and @code{UNSIGNED_LONGWORD} forms of @code{TO_ADDRESS}. However, in HP Ada 83, there is no ambiguity, since the definition using @i{universal_integer} takes precedence. In GNAT, since the version with @i{universal_integer} cannot be supplied, it is not possible to be 100% compatible. Since there are many programs using numeric constants for the argument to @code{TO_ADDRESS}, the decision in GNAT was to change the name of the function in the @code{UNSIGNED_LONGWORD} case, so the declarations provided in the GNAT version of @code{AUX_Dec} are: @smallexample @c ada function To_Address (X : Integer) return Address; pragma Pure_Function (To_Address); function To_Address_Long (X : Unsigned_Longword) return Address; pragma Pure_Function (To_Address_Long); @end smallexample @noindent This means that programs using @code{TO_ADDRESS} for @code{UNSIGNED_LONGWORD} must change the name to @code{TO_ADDRESS_LONG}. @node Tasking and Task-Related Features @section Tasking and Task-Related Features @noindent This section compares the treatment of tasking in GNAT and in HP Ada for OpenVMS Alpha. The GNAT description applies to both Alpha and I64 OpenVMS. For detailed information on tasking in HP Ada, see the @cite{HP Ada Language Reference Manual} and the relevant run-time reference manual. @menu * Implementation of Tasks in HP Ada for OpenVMS Alpha Systems:: * Assigning Task IDs:: * Task IDs and Delays:: * Task-Related Pragmas:: * Scheduling and Task Priority:: * The Task Stack:: * External Interrupts:: @end menu @node Implementation of Tasks in HP Ada for OpenVMS Alpha Systems @subsection Implementation of Tasks in HP Ada for OpenVMS Alpha Systems @noindent On OpenVMS Alpha systems, each Ada task (except a passive task) is implemented as a single stream of execution that is created and managed by the kernel. On these systems, HP Ada tasking support is based on DECthreads, an implementation of the POSIX standard for threads. Also, on OpenVMS Alpha systems, HP Ada tasks and foreign code that calls DECthreads routines can be used together. The interaction between Ada tasks and DECthreads routines can have some benefits. For example when on OpenVMS Alpha, HP Ada can call C code that is already threaded. GNAT uses the facilities of DECthreads, and Ada tasks are mapped to threads. @node Assigning Task IDs @subsection Assigning Task IDs @noindent The HP Ada Run-Time Library always assigns @code{%TASK 1} to the environment task that executes the main program. On OpenVMS Alpha systems, @code{%TASK 0} is often used for tasks that have been created but are not yet activated. On OpenVMS Alpha systems, task IDs are assigned at activation. On GNAT systems, task IDs are also assigned at task creation but do not have the same form or values as task ID values in HP Ada. There is no null task, and the environment task does not have a specific task ID value. @node Task IDs and Delays @subsection Task IDs and Delays @noindent On OpenVMS Alpha systems, tasking delays are implemented using Timer System Services. The Task ID is used for the identification of the timer request (the @code{REQIDT} parameter). If Timers are used in the application take care not to use @code{0} for the identification, because cancelling such a timer will cancel all timers and may lead to unpredictable results. @node Task-Related Pragmas @subsection Task-Related Pragmas @noindent Ada supplies the pragma @code{TASK_STORAGE}, which allows specification of the size of the guard area for a task stack. (The guard area forms an area of memory that has no read or write access and thus helps in the detection of stack overflow.) On OpenVMS Alpha systems, if the pragma @code{TASK_STORAGE} specifies a value of zero, a minimal guard area is created. In the absence of a pragma @code{TASK_STORAGE}, a default guard area is created. GNAT supplies the following task-related pragmas: @itemize @bullet @item @code{TASK_INFO} This pragma appears within a task definition and applies to the task in which it appears. The argument must be of type @code{SYSTEM.TASK_INFO.TASK_INFO_TYPE}. @item @code{TASK_STORAGE} GNAT implements pragma @code{TASK_STORAGE} in the same way as HP Ada. Both HP Ada and GNAT supply the pragmas @code{PASSIVE}, @code{SUPPRESS}, and @code{VOLATILE}. @end itemize @node Scheduling and Task Priority @subsection Scheduling and Task Priority @noindent HP Ada implements the Ada language requirement that when two tasks are eligible for execution and they have different priorities, the lower priority task does not execute while the higher priority task is waiting. The HP Ada Run-Time Library keeps a task running until either the task is suspended or a higher priority task becomes ready. On OpenVMS Alpha systems, the default strategy is round- robin with preemption. Tasks of equal priority take turns at the processor. A task is run for a certain period of time and then placed at the tail of the ready queue for its priority level. HP Ada provides the implementation-defined pragma @code{TIME_SLICE}, which can be used to enable or disable round-robin scheduling of tasks with the same priority. See the relevant HP Ada run-time reference manual for information on using the pragmas to control HP Ada task scheduling. GNAT follows the scheduling rules of Annex D (Real-Time Annex) of the @cite{Ada Reference Manual}. In general, this scheduling strategy is fully compatible with HP Ada although it provides some additional constraints (as fully documented in Annex D). GNAT implements time slicing control in a manner compatible with HP Ada 83, by means of the pragma @code{Time_Slice}, whose semantics are identical to the HP Ada 83 pragma of the same name. Note that it is not possible to mix GNAT tasking and HP Ada 83 tasking in the same program, since the two run-time libraries are not compatible. @node The Task Stack @subsection The Task Stack @noindent In HP Ada, a task stack is allocated each time a non-passive task is activated. As soon as the task is terminated, the storage for the task stack is deallocated. If you specify a size of zero (bytes) with @code{T'STORAGE_SIZE}, a default stack size is used. Also, regardless of the size specified, some additional space is allocated for task management purposes. On OpenVMS Alpha systems, at least one page is allocated. GNAT handles task stacks in a similar manner. In accordance with the Ada rules, it provides the pragma @code{STORAGE_SIZE} as an alternative method for controlling the task stack size. The specification of the attribute @code{T'STORAGE_SIZE} is also supported in a manner compatible with HP Ada. @node External Interrupts @subsection External Interrupts @noindent On HP Ada, external interrupts can be associated with task entries. GNAT is compatible with HP Ada in its handling of external interrupts. @node Pragmas and Pragma-Related Features @section Pragmas and Pragma-Related Features @noindent Both HP Ada and GNAT supply all language-defined pragmas as specified by the Ada 83 standard. GNAT also supplies all language-defined pragmas introduced by Ada 95 and Ada 2005. In addition, GNAT implements the implementation-defined pragmas from HP Ada 83. @itemize @bullet @item @code{AST_ENTRY} @item @code{COMMON_OBJECT} @item @code{COMPONENT_ALIGNMENT} @item @code{EXPORT_EXCEPTION} @item @code{EXPORT_FUNCTION} @item @code{EXPORT_OBJECT} @item @code{EXPORT_PROCEDURE} @item @code{EXPORT_VALUED_PROCEDURE} @item @code{FLOAT_REPRESENTATION} @item @code{IDENT} @item @code{IMPORT_EXCEPTION} @item @code{IMPORT_FUNCTION} @item @code{IMPORT_OBJECT} @item @code{IMPORT_PROCEDURE} @item @code{IMPORT_VALUED_PROCEDURE} @item @code{INLINE_GENERIC} @item @code{INTERFACE_NAME} @item @code{LONG_FLOAT} @item @code{MAIN_STORAGE} @item @code{PASSIVE} @item @code{PSECT_OBJECT} @item @code{SHARE_GENERIC} @item @code{SUPPRESS_ALL} @item @code{TASK_STORAGE} @item @code{TIME_SLICE} @item @code{TITLE} @end itemize @noindent These pragmas are all fully implemented, with the exception of @code{TITLE}, @code{PASSIVE}, and @code{SHARE_GENERIC}, which are recognized, but which have no effect in GNAT. The effect of @code{PASSIVE} may be obtained by the use of Ada protected objects. In GNAT, all generics are inlined. Unlike HP Ada, the GNAT ``@code{EXPORT_}@i{subprogram}'' pragmas require a separate subprogram specification which must appear before the subprogram body. GNAT also supplies a number of implementation-defined pragmas including the following: @itemize @bullet @item @code{ABORT_DEFER} @item @code{ADA_83} @item @code{ADA_95} @item @code{ADA_05} @item @code{Ada_2005} @item @code{Ada_12} @item @code{Ada_2012} @item @code{ANNOTATE} @item @code{ASSERT} @item @code{C_PASS_BY_COPY} @item @code{CPP_CLASS} @item @code{CPP_CONSTRUCTOR} @item @code{CPP_DESTRUCTOR} @item @code{DEBUG} @item @code{EXTEND_SYSTEM} @item @code{LINKER_ALIAS} @item @code{LINKER_SECTION} @item @code{MACHINE_ATTRIBUTE} @item @code{NO_RETURN} @item @code{PURE_FUNCTION} @item @code{SOURCE_FILE_NAME} @item @code{SOURCE_REFERENCE} @item @code{TASK_INFO} @item @code{UNCHECKED_UNION} @item @code{UNIMPLEMENTED_UNIT} @item @code{UNIVERSAL_DATA} @item @code{UNSUPPRESS} @item @code{WARNINGS} @item @code{WEAK_EXTERNAL} @end itemize @noindent For full details on these and other GNAT implementation-defined pragmas, see @ref{Implementation Defined Pragmas,,, gnat_rm, GNAT Reference Manual}. @menu * Restrictions on the Pragma INLINE:: * Restrictions on the Pragma INTERFACE:: * Restrictions on the Pragma SYSTEM_NAME:: @end menu @node Restrictions on the Pragma INLINE @subsection Restrictions on Pragma @code{INLINE} @noindent HP Ada enforces the following restrictions on the pragma @code{INLINE}: @itemize @bullet @item Parameters cannot have a task type. @item Function results cannot be task types, unconstrained array types, or unconstrained types with discriminants. @item Bodies cannot declare the following: @itemize @bullet @item Subprogram body or stub (imported subprogram is allowed) @item Tasks @item Generic declarations @item Instantiations @item Exceptions @item Access types (types derived from access types allowed) @item Array or record types @item Dependent tasks @item Direct recursive calls of subprogram or containing subprogram, directly or via a renaming @end itemize @end itemize @noindent In GNAT, the only restriction on pragma @code{INLINE} is that the body must occur before the call if both are in the same unit, and the size must be appropriately small. There are no other specific restrictions which cause subprograms to be incapable of being inlined. @node Restrictions on the Pragma INTERFACE @subsection Restrictions on Pragma @code{INTERFACE} @noindent The following restrictions on pragma @code{INTERFACE} are enforced by both HP Ada and GNAT: @itemize @bullet @item Languages accepted: Ada, Bliss, C, Fortran, Default. Default is the default on OpenVMS Alpha systems. @item Parameter passing: Language specifies default mechanisms but can be overridden with an @code{EXPORT} pragma. @itemize @bullet @item Ada: Use internal Ada rules. @item Bliss, C: Parameters must be mode @code{in}; cannot be record or task type. Result cannot be a string, an array, or a record. @item Fortran: Parameters cannot have a task type. Result cannot be a string, an array, or a record. @end itemize @end itemize @noindent GNAT is entirely upwards compatible with HP Ada, and in addition allows record parameters for all languages. @node Restrictions on the Pragma SYSTEM_NAME @subsection Restrictions on Pragma @code{SYSTEM_NAME} @noindent For HP Ada for OpenVMS Alpha, the enumeration literal for the type @code{NAME} is @code{OPENVMS_AXP}. In GNAT, the enumeration literal for the type @code{NAME} is @code{SYSTEM_NAME_GNAT}. @node Library of Predefined Units @section Library of Predefined Units @noindent A library of predefined units is provided as part of the HP Ada and GNAT implementations. HP Ada does not provide the package @code{MACHINE_CODE} but instead recommends importing assembler code. The GNAT versions of the HP Ada Run-Time Library (@code{ADA$PREDEFINED:}) units are taken from the OpenVMS Alpha version, not the OpenVMS VAX version. The HP Ada Predefined Library units are modified to remove post-Ada 83 incompatibilities and to make them interoperable with GNAT (@pxref{Changes to DECLIB}, for details). The units are located in the @file{DECLIB} directory. The GNAT RTL is contained in the @file{ADALIB} directory, and the default search path is set up to find @code{DECLIB} units in preference to @code{ADALIB} units with the same name (@code{TEXT_IO}, @code{SEQUENTIAL_IO}, and @code{DIRECT_IO}, for example). @menu * Changes to DECLIB:: @end menu @node Changes to DECLIB @subsection Changes to @code{DECLIB} @noindent The changes made to the HP Ada predefined library for GNAT and post-Ada 83 compatibility are minor and include the following: @itemize @bullet @item Adjusting the location of pragmas and record representation clauses to obey Ada 95 (and thus Ada 2005) rules @item Adding the proper notation to generic formal parameters that take unconstrained types in instantiation @item Adding pragma @code{ELABORATE_BODY} to package specs that have package bodies not otherwise allowed @item Replacing occurrences of the identifier ``@code{PROTECTED}'' by ``@code{PROTECTD}''. Currently these are found only in the @code{STARLET} package spec. @item Changing @code{SYSTEM.ADDRESS} to @code{SYSTEM.SHORT_ADDRESS} where the address size is constrained to 32 bits. @end itemize @noindent None of the above changes is visible to users. @node Bindings @section Bindings @noindent On OpenVMS Alpha, HP Ada provides the following strongly-typed bindings: @itemize @bullet @item Command Language Interpreter (CLI interface) @item DECtalk Run-Time Library (DTK interface) @item Librarian utility routines (LBR interface) @item General Purpose Run-Time Library (LIB interface) @item Math Run-Time Library (MTH interface) @item National Character Set Run-Time Library (NCS interface) @item Compiled Code Support Run-Time Library (OTS interface) @item Parallel Processing Run-Time Library (PPL interface) @item Screen Management Run-Time Library (SMG interface) @item Sort Run-Time Library (SOR interface) @item String Run-Time Library (STR interface) @item STARLET System Library @findex Starlet @item X Window System Version 11R4 and 11R5 (X, XLIB interface) @item X Windows Toolkit (XT interface) @item X/Motif Version 1.1.3 and 1.2 (XM interface) @end itemize @noindent GNAT provides implementations of these HP bindings in the @code{DECLIB} directory, on both the Alpha and I64 OpenVMS platforms. The X/Motif bindings used to build @code{DECLIB} are whatever versions are in the HP Ada @file{ADA$PREDEFINED} directory with extension @file{.ADC}. A pragma @code{Linker_Options} has been added to packages @code{Xm}, @code{Xt}, and @code{X_Lib} causing the default X/Motif sharable image libraries to be linked in. This is done via options files named @file{xm.opt}, @file{xt.opt}, and @file{x_lib.opt} (also located in the @file{DECLIB} directory). It may be necessary to edit these options files to update or correct the library names if, for example, the newer X/Motif bindings from @file{ADA$EXAMPLES} had been (previous to installing GNAT) copied and renamed to supersede the default @file{ADA$PREDEFINED} versions. @menu * Shared Libraries and Options Files:: * Interfaces to C:: @end menu @node Shared Libraries and Options Files @subsection Shared Libraries and Options Files @noindent When using the HP Ada predefined X and Motif bindings, the linking with their sharable images is done automatically by @command{GNAT LINK}. When using other X and Motif bindings, you need to add the corresponding sharable images to the command line for @code{GNAT LINK}. When linking with shared libraries, or with @file{.OPT} files, you must also add them to the command line for @command{GNAT LINK}. A shared library to be used with GNAT is built in the same way as other libraries under VMS. The VMS Link command can be used in standard fashion. @node Interfaces to C @subsection Interfaces to C @noindent HP Ada provides the following Ada types and operations: @itemize @bullet @item C types package (@code{C_TYPES}) @item C strings (@code{C_TYPES.NULL_TERMINATED}) @item Other_types (@code{SHORT_INT}) @end itemize @noindent Interfacing to C with GNAT, you can use the above approach described for HP Ada or the facilities of Annex B of the @cite{Ada Reference Manual} (packages @code{INTERFACES.C}, @code{INTERFACES.C.STRINGS} and @code{INTERFACES.C.POINTERS}). For more information, see @ref{Interfacing to C,,, gnat_rm, GNAT Reference Manual}. The @option{-gnatF} qualifier forces default and explicit @code{External_Name} parameters in pragmas @code{Import} and @code{Export} to be uppercased for compatibility with the default behavior of HP C. The qualifier has no effect on @code{Link_Name} parameters. @node Main Program Definition @section Main Program Definition @noindent The following section discusses differences in the definition of main programs on HP Ada and GNAT. On HP Ada, main programs are defined to meet the following conditions: @itemize @bullet @item Procedure with no formal parameters (returns @code{0} upon normal completion) @item Procedure with no formal parameters (returns @code{42} when an unhandled exception is raised) @item Function with no formal parameters whose returned value is of a discrete type @item Procedure with one @code{out} formal of a discrete type for which a specification of pragma @code{EXPORT_VALUED_PROCEDURE} is given. @end itemize @noindent When declared with the pragma @code{EXPORT_VALUED_PROCEDURE}, a main function or main procedure returns a discrete value whose size is less than 64 bits (32 on VAX systems), the value is zero- or sign-extended as appropriate. On GNAT, main programs are defined as follows: @itemize @bullet @item Must be a non-generic, parameterless subprogram that is either a procedure or function returning an Ada @code{STANDARD.INTEGER} (the predefined type) @item Cannot be a generic subprogram or an instantiation of a generic subprogram @end itemize @node Implementation-Defined Attributes @section Implementation-Defined Attributes @noindent GNAT provides all HP Ada implementation-defined attributes. @node Compiler and Run-Time Interfacing @section Compiler and Run-Time Interfacing @noindent HP Ada provides the following qualifiers to pass options to the linker (ACS LINK): @itemize @bullet @item @option{/WAIT} and @option{/SUBMIT} @item @option{/COMMAND} @item @option{/@r{[}NO@r{]}MAP} @item @option{/OUTPUT=@var{file-spec}} @item @option{/@r{[}NO@r{]}DEBUG} and @option{/@r{[}NO@r{]}TRACEBACK} @end itemize @noindent To pass options to the linker, GNAT provides the following switches: @itemize @bullet @item @option{/EXECUTABLE=@var{exec-name}} @item @option{/VERBOSE} @item @option{/@r{[}NO@r{]}DEBUG} and @option{/@r{[}NO@r{]}TRACEBACK} @end itemize @noindent For more information on these switches, see @ref{Switches for gnatlink}. In HP Ada, the command-line switch @option{/OPTIMIZE} is available to control optimization. HP Ada also supplies the following pragmas: @itemize @bullet @item @code{OPTIMIZE} @item @code{INLINE} @item @code{INLINE_GENERIC} @item @code{SUPPRESS_ALL} @item @code{PASSIVE} @end itemize @noindent In GNAT, optimization is controlled strictly by command line parameters, as described in the corresponding section of this guide. The HP pragmas for control of optimization are recognized but ignored. Note that in GNAT, the default is optimization off, whereas in HP Ada the default is that optimization is turned on. @node Program Compilation and Library Management @section Program Compilation and Library Management @noindent HP Ada and GNAT provide a comparable set of commands to build programs. HP Ada also provides a program library, which is a concept that does not exist on GNAT. Instead, GNAT provides directories of sources that are compiled as needed. The following table summarizes the HP Ada commands and provides equivalent GNAT commands. In this table, some GNAT equivalents reflect the fact that GNAT does not use the concept of a program library. Instead, it uses a model in which collections of source and object files are used in a manner consistent with other languages like C and Fortran. Therefore, standard system file commands are used to manipulate these elements. Those GNAT commands are marked with an asterisk. Note that, unlike HP Ada, none of the GNAT commands accepts wild cards. @need 1500 @multitable @columnfractions .35 .65 @item @emph{HP Ada Command} @tab @emph{GNAT Equivalent / Description} @item @command{ADA} @tab @command{GNAT COMPILE}@* Invokes the compiler to compile one or more Ada source files. @item @command{ACS ATTACH}@* @tab [No equivalent]@* Switches control of terminal from current process running the program library manager. @item @command{ACS CHECK} @tab @command{GNAT MAKE /DEPENDENCY_LIST}@* Forms the execution closure of one or more compiled units and checks completeness and currency. @item @command{ACS COMPILE} @tab @command{GNAT MAKE /ACTIONS=COMPILE}@* Forms the execution closure of one or more specified units, checks completeness and currency, identifies units that have revised source files, compiles same, and recompiles units that are or will become obsolete. Also completes incomplete generic instantiations. @item @command{ACS COPY FOREIGN} @tab Copy (*)@* Copies a foreign object file into the program library as a library unit body. @item @command{ACS COPY UNIT} @tab Copy (*)@* Copies a compiled unit from one program library to another. @item @command{ACS CREATE LIBRARY} @tab Create /directory (*)@* Creates a program library. @item @command{ACS CREATE SUBLIBRARY} @tab Create /directory (*)@* Creates a program sublibrary. @item @command{ACS DELETE LIBRARY} @tab @* Deletes a program library and its contents. @item @command{ACS DELETE SUBLIBRARY} @tab @* Deletes a program sublibrary and its contents. @item @command{ACS DELETE UNIT} @tab Delete file (*)@* On OpenVMS systems, deletes one or more compiled units from the current program library. @item @command{ACS DIRECTORY} @tab Directory (*)@* On OpenVMS systems, lists units contained in the current program library. @item @command{ACS ENTER FOREIGN} @tab Copy (*)@* Allows the import of a foreign body as an Ada library spec and enters a reference to a pointer. @item @command{ACS ENTER UNIT} @tab Copy (*)@* Enters a reference (pointer) from the current program library to a unit compiled into another program library. @item @command{ACS EXIT} @tab [No equivalent]@* Exits from the program library manager. @item @command{ACS EXPORT} @tab Copy (*)@* Creates an object file that contains system-specific object code for one or more units. With GNAT, object files can simply be copied into the desired directory. @item @command{ACS EXTRACT SOURCE} @tab Copy (*)@* Allows access to the copied source file for each Ada compilation unit @item @command{ACS HELP} @tab @command{HELP GNAT}@* Provides online help. @item @command{ACS LINK} @tab @command{GNAT LINK}@* Links an object file containing Ada units into an executable file. @item @command{ACS LOAD} @tab Copy (*)@* Loads (partially compiles) Ada units into the program library. Allows loading a program from a collection of files into a library without knowing the relationship among units. @item @command{ACS MERGE} @tab Copy (*)@* Merges into the current program library, one or more units from another library where they were modified. @item @command{ACS RECOMPILE} @tab @command{GNAT MAKE /ACTIONS=COMPILE}@* Recompiles from external or copied source files any obsolete unit in the closure. Also, completes any incomplete generic instantiations. @item @command{ACS REENTER} @tab @command{GNAT MAKE}@* Reenters current references to units compiled after last entered with the @command{ACS ENTER UNIT} command. @item @command{ACS SET LIBRARY} @tab Set default (*)@* Defines a program library to be the compilation context as well as the target library for compiler output and commands in general. @item @command{ACS SET PRAGMA} @tab Edit @file{gnat.adc} (*)@* Redefines specified values of the library characteristics @code{LONG_ FLOAT}, @code{MEMORY_SIZE}, @code{SYSTEM_NAME}, and @code{Float_Representation}. @item @command{ACS SET SOURCE} @tab Define @code{ADA_INCLUDE_PATH} path (*)@* Defines the source file search list for the @command{ACS COMPILE} command. @item @command{ACS SHOW LIBRARY} @tab Directory (*)@* Lists information about one or more program libraries. @item @command{ACS SHOW PROGRAM} @tab [No equivalent]@* Lists information about the execution closure of one or more units in the program library. @item @command{ACS SHOW SOURCE} @tab Show logical @code{ADA_INCLUDE_PATH}@* Shows the source file search used when compiling units. @item @command{ACS SHOW VERSION} @tab Compile with @option{VERBOSE} option Displays the version number of the compiler and program library manager used. @item @command{ACS SPAWN} @tab [No equivalent]@* Creates a subprocess of the current process (same as @command{DCL SPAWN} command). @item @command{ACS VERIFY} @tab [No equivalent]@* Performs a series of consistency checks on a program library to determine whether the library structure and library files are in valid form. @end multitable @noindent @node Input-Output @section Input-Output @noindent On OpenVMS Alpha systems, HP Ada uses OpenVMS Record Management Services (RMS) to perform operations on external files. @noindent HP Ada and GNAT predefine an identical set of input- output packages. To make the use of the generic @code{TEXT_IO} operations more convenient, HP Ada provides predefined library packages that instantiate the integer and floating-point operations for the predefined integer and floating-point types as shown in the following table. @multitable @columnfractions .45 .55 @item @emph{Package Name} @tab Instantiation @item @code{INTEGER_TEXT_IO} @tab @code{INTEGER_IO(INTEGER)} @item @code{SHORT_INTEGER_TEXT_IO} @tab @code{INTEGER_IO(SHORT_INTEGER)} @item @code{SHORT_SHORT_INTEGER_TEXT_IO} @tab @code{INTEGER_IO(SHORT_SHORT_INTEGER)} @item @code{FLOAT_TEXT_IO} @tab @code{FLOAT_IO(FLOAT)} @item @code{LONG_FLOAT_TEXT_IO} @tab @code{FLOAT_IO(LONG_FLOAT)} @end multitable @noindent The HP Ada predefined packages and their operations are implemented using OpenVMS Alpha files and input-output facilities. HP Ada supports asynchronous input-output on OpenVMS Alpha. Familiarity with the following is recommended: @itemize @bullet @item RMS file organizations and access methods @item OpenVMS file specifications and directories @item OpenVMS File Definition Language (FDL) @end itemize @noindent GNAT provides I/O facilities that are completely compatible with HP Ada. The distribution includes the standard HP Ada versions of all I/O packages, operating in a manner compatible with HP Ada. In particular, the following packages are by default the HP Ada (Ada 83) versions of these packages rather than the renamings suggested in Annex J of the Ada Reference Manual: @itemize @bullet @item @code{TEXT_IO} @item @code{SEQUENTIAL_IO} @item @code{DIRECT_IO} @end itemize @noindent The use of the standard child package syntax (for example, @code{ADA.TEXT_IO}) retrieves the post-Ada 83 versions of these packages. GNAT provides HP-compatible predefined instantiations of the @code{TEXT_IO} packages, and also provides the standard predefined instantiations required by the @cite{Ada Reference Manual}. For further information on how GNAT interfaces to the file system or how I/O is implemented in programs written in mixed languages, see @ref{Implementation of the Standard I/O,,, gnat_rm, GNAT Reference Manual}. This chapter covers the following: @itemize @bullet @item Standard I/O packages @item @code{FORM} strings @item @code{ADA.DIRECT_IO} @item @code{ADA.SEQUENTIAL_IO} @item @code{ADA.TEXT_IO} @item Stream pointer positioning @item Reading and writing non-regular files @item @code{GET_IMMEDIATE} @item Treating @code{TEXT_IO} files as streams @item Shared files @item Open modes @end itemize @node Implementation Limits @section Implementation Limits @noindent The following table lists implementation limits for HP Ada and GNAT systems. @multitable @columnfractions .60 .20 .20 @sp 1 @item @emph{Compilation Parameter} @tab @emph{HP Ada} @tab @emph{GNAT} @sp 1 @item In a subprogram or entry declaration, maximum number of formal parameters that are of an unconstrained record type @tab 32 @tab No set limit @sp 1 @item Maximum identifier length (number of characters) @tab 255 @tab 32766 @sp 1 @item Maximum number of characters in a source line @tab 255 @tab 32766 @sp 1 @item Maximum collection size (number of bytes) @tab 2**31-1 @tab 2**31-1 @sp 1 @item Maximum number of discriminants for a record type @tab 245 @tab No set limit @sp 1 @item Maximum number of formal parameters in an entry or subprogram declaration @tab 246 @tab No set limit @sp 1 @item Maximum number of dimensions in an array type @tab 255 @tab No set limit @sp 1 @item Maximum number of library units and subunits in a compilation. @tab 4095 @tab No set limit @sp 1 @item Maximum number of library units and subunits in an execution. @tab 16383 @tab No set limit @sp 1 @item Maximum number of objects declared with the pragma @code{COMMON_OBJECT} or @code{PSECT_OBJECT} @tab 32757 @tab No set limit @sp 1 @item Maximum number of enumeration literals in an enumeration type definition @tab 65535 @tab No set limit @sp 1 @item Maximum number of lines in a source file @tab 65534 @tab No set limit @sp 1 @item Maximum number of bits in any object @tab 2**31-1 @tab 2**31-1 @sp 1 @item Maximum size of the static portion of a stack frame (approximate) @tab 2**31-1 @tab 2**31-1 @end multitable @node Tools and Utilities @section Tools and Utilities @noindent The following table lists some of the OpenVMS development tools available for HP Ada, and the corresponding tools for use with @value{EDITION} on Alpha and I64 platforms. Aside from the debugger, all the OpenVMS tools identified are part of the DECset package. @iftex @c Specify table in TeX since Texinfo does a poor job @tex \smallskip \smallskip \settabs\+Language-Sensitive Editor\quad &Product with HP Ada\quad &\cr \+\it Tool &\it Product with HP Ada & \it Product with GNAT Pro\cr \smallskip \+Code Management System &HP CMS & HP CMS\cr \smallskip \+Language-Sensitive Editor &HP LSE & emacs or HP LSE (Alpha)\cr \+ & & HP LSE (I64)\cr \smallskip \+Debugger &OpenVMS Debug & gdb (Alpha),\cr \+ & & OpenVMS Debug (I64)\cr \smallskip \+Source Code Analyzer / &HP SCA & GNAT XREF\cr \+Cross Referencer & &\cr \smallskip \+Test Manager &HP Digital Test & HP DTM\cr \+ &Manager (DTM) &\cr \smallskip \+Performance and & HP PCA & HP PCA\cr \+Coverage Analyzer & &\cr \smallskip \+Module Management & HP MMS & Not applicable\cr \+ System & &\cr \smallskip \smallskip @end tex @end iftex @ifnottex @c This is the Texinfo version of the table. It renders poorly in pdf, hence @c the TeX version above for the printed version @flushleft @c @multitable @columnfractions .3 .4 .4 @multitable {Source Code Analyzer /}{Tool with HP Ada}{Tool with GNAT Pro} @item @i{Tool} @tab @i{Tool with HP Ada} @tab @i{Tool with @value{EDITION}} @item Code Management@*System @tab HP CMS @tab HP CMS @item Language-Sensitive@*Editor @tab HP LSE @tab emacs or HP LSE (Alpha) @item @tab @tab HP LSE (I64) @item Debugger @tab OpenVMS Debug @tab gdb (Alpha), @item @tab @tab OpenVMS Debug (I64) @item Source Code Analyzer /@*Cross Referencer @tab HP SCA @tab GNAT XREF @item Test Manager @tab HP Digital Test@*Manager (DTM) @tab HP DTM @item Performance and@*Coverage Analyzer @tab HP PCA @tab HP PCA @item Module Management@*System @tab HP MMS @tab Not applicable @end multitable @end flushleft @end ifnottex @end ifset @c ************************************** @node Platform-Specific Information for the Run-Time Libraries @appendix Platform-Specific Information for the Run-Time Libraries @cindex Tasking and threads libraries @cindex Threads libraries and tasking @cindex Run-time libraries (platform-specific information) @noindent The GNAT run-time implementation may vary with respect to both the underlying threads library and the exception handling scheme. For threads support, one or more of the following are supplied: @itemize @bullet @item @b{native threads library}, a binding to the thread package from the underlying operating system @item @b{pthreads library} (Sparc Solaris only), a binding to the Solaris POSIX thread package @end itemize @noindent For exception handling, either or both of two models are supplied: @itemize @bullet @item @b{Zero-Cost Exceptions} (``ZCX''),@footnote{ Most programs should experience a substantial speed improvement by being compiled with a ZCX run-time. This is especially true for tasking applications or applications with many exception handlers.} @cindex Zero-Cost Exceptions @cindex ZCX (Zero-Cost Exceptions) which uses binder-generated tables that are interrogated at run time to locate a handler @item @b{setjmp / longjmp} (``SJLJ''), @cindex setjmp/longjmp Exception Model @cindex SJLJ (setjmp/longjmp Exception Model) which uses dynamically-set data to establish the set of handlers @end itemize @noindent This appendix summarizes which combinations of threads and exception support are supplied on various GNAT platforms. It then shows how to select a particular library either permanently or temporarily, explains the properties of (and tradeoffs among) the various threads libraries, and provides some additional information about several specific platforms. @menu * Summary of Run-Time Configurations:: * Specifying a Run-Time Library:: * Choosing the Scheduling Policy:: * Solaris-Specific Considerations:: * Linux-Specific Considerations:: * AIX-Specific Considerations:: * Irix-Specific Considerations:: * RTX-Specific Considerations:: * HP-UX-Specific Considerations:: @end menu @node Summary of Run-Time Configurations @section Summary of Run-Time Configurations @multitable @columnfractions .30 .70 @item @b{alpha-openvms} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native VMS threads @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{alpha-tru64} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native TRU64 threads @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @code{@ @ }@i{rts-sjlj} @item @code{@ @ @ @ }Tasking @tab native TRU64 threads @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{ia64-hp_linux} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab pthread library @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{ia64-hpux} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native HP-UX threads @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{ia64-openvms} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native VMS threads @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{ia64-sgi_linux} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab pthread library @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{mips-irix} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native IRIX threads @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{pa-hpux} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native HP-UX threads @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @code{@ @ }@i{rts-sjlj} @item @code{@ @ @ @ }Tasking @tab native HP-UX threads @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{ppc-aix} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native AIX threads @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{ppc-darwin} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native MacOS threads @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{sparc-solaris} @tab @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native Solaris threads library @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @code{@ @ }@i{rts-pthread} @item @code{@ @ @ @ }Tasking @tab pthread library @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @code{@ @ }@i{rts-sjlj} @item @code{@ @ @ @ }Tasking @tab native Solaris threads library @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{sparc64-solaris} @tab @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native Solaris threads library @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{x86-linux} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab pthread library @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @code{@ @ }@i{rts-sjlj} @item @code{@ @ @ @ }Tasking @tab pthread library @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{x86-lynx} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native LynxOS threads @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{x86-solaris} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native Solaris threads @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{x86-windows} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab native Win32 threads @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @code{@ @ }@i{rts-sjlj (default)} @item @code{@ @ @ @ }Tasking @tab native Win32 threads @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @b{x86-windows-rtx} @item @code{@ @ }@i{rts-rtx-rtss (default)} @item @code{@ @ @ @ }Tasking @tab RTX real-time subsystem RTSS threads (kernel mode) @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @item @code{@ @ }@i{rts-rtx-w32} @item @code{@ @ @ @ }Tasking @tab RTX Win32 threads (user mode) @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @b{x86_64-linux} @item @code{@ @ }@i{rts-native (default)} @item @code{@ @ @ @ }Tasking @tab pthread library @item @code{@ @ @ @ }Exceptions @tab ZCX @* @item @code{@ @ }@i{rts-sjlj} @item @code{@ @ @ @ }Tasking @tab pthread library @item @code{@ @ @ @ }Exceptions @tab SJLJ @* @end multitable @node Specifying a Run-Time Library @section Specifying a Run-Time Library @noindent The @file{adainclude} subdirectory containing the sources of the GNAT run-time library, and the @file{adalib} subdirectory containing the @file{ALI} files and the static and/or shared GNAT library, are located in the gcc target-dependent area: @smallexample target=$prefix/lib/gcc/gcc-@i{dumpmachine}/gcc-@i{dumpversion}/ @end smallexample @noindent As indicated above, on some platforms several run-time libraries are supplied. These libraries are installed in the target dependent area and contain a complete source and binary subdirectory. The detailed description below explains the differences between the different libraries in terms of their thread support. The default run-time library (when GNAT is installed) is @emph{rts-native}. This default run time is selected by the means of soft links. For example on x86-linux: @smallexample @group $(target-dir) | +--- adainclude----------+ | | +--- adalib-----------+ | | | | +--- rts-native | | | | | | | +--- adainclude <---+ | | | | +--- adalib <----+ | +--- rts-sjlj | +--- adainclude | +--- adalib @end group @end smallexample @noindent If the @i{rts-sjlj} library is to be selected on a permanent basis, these soft links can be modified with the following commands: @smallexample $ cd $target $ rm -f adainclude adalib $ ln -s rts-sjlj/adainclude adainclude $ ln -s rts-sjlj/adalib adalib @end smallexample @noindent Alternatively, you can specify @file{rts-sjlj/adainclude} in the file @file{$target/ada_source_path} and @file{rts-sjlj/adalib} in @file{$target/ada_object_path}. Selecting another run-time library temporarily can be achieved by using the @option{--RTS} switch, e.g., @option{--RTS=sjlj} @cindex @option{--RTS} option @node Choosing the Scheduling Policy @section Choosing the Scheduling Policy @noindent When using a POSIX threads implementation, you have a choice of several scheduling policies: @code{SCHED_FIFO}, @cindex @code{SCHED_FIFO} scheduling policy @code{SCHED_RR} @cindex @code{SCHED_RR} scheduling policy and @code{SCHED_OTHER}. @cindex @code{SCHED_OTHER} scheduling policy Typically, the default is @code{SCHED_OTHER}, while using @code{SCHED_FIFO} or @code{SCHED_RR} requires special (e.g., root) privileges. By default, GNAT uses the @code{SCHED_OTHER} policy. To specify @code{SCHED_FIFO}, @cindex @code{SCHED_FIFO} scheduling policy you can use one of the following: @itemize @bullet @item @code{pragma Time_Slice (0.0)} @cindex pragma Time_Slice @item the corresponding binder option @option{-T0} @cindex @option{-T0} option @item @code{pragma Task_Dispatching_Policy (FIFO_Within_Priorities)} @cindex pragma Task_Dispatching_Policy @end itemize @noindent To specify @code{SCHED_RR}, @cindex @code{SCHED_RR} scheduling policy you should use @code{pragma Time_Slice} with a value greater than @code{0.0}, or else use the corresponding @option{-T} binder option. @node Solaris-Specific Considerations @section Solaris-Specific Considerations @cindex Solaris Sparc threads libraries @noindent This section addresses some topics related to the various threads libraries on Sparc Solaris. @menu * Solaris Threads Issues:: @end menu @node Solaris Threads Issues @subsection Solaris Threads Issues @noindent GNAT under Solaris/Sparc 32 bits comes with an alternate tasking run-time library based on POSIX threads --- @emph{rts-pthread}. @cindex rts-pthread threads library This run-time library has the advantage of being mostly shared across all POSIX-compliant thread implementations, and it also provides under @w{Solaris 8} the @code{PTHREAD_PRIO_INHERIT} @cindex @code{PTHREAD_PRIO_INHERIT} policy (under rts-pthread) and @code{PTHREAD_PRIO_PROTECT} @cindex @code{PTHREAD_PRIO_PROTECT} policy (under rts-pthread) semantics that can be selected using the predefined pragma @code{Locking_Policy} @cindex pragma Locking_Policy (under rts-pthread) with respectively @code{Inheritance_Locking} and @code{Ceiling_Locking} as the policy. @cindex @code{Inheritance_Locking} (under rts-pthread) @cindex @code{Ceiling_Locking} (under rts-pthread) As explained above, the native run-time library is based on the Solaris thread library (@code{libthread}) and is the default library. When the Solaris threads library is used (this is the default), programs compiled with GNAT can automatically take advantage of and can thus execute on multiple processors. The user can alternatively specify a processor on which the program should run to emulate a single-processor system. The multiprocessor / uniprocessor choice is made by setting the environment variable @env{GNAT_PROCESSOR} @cindex @env{GNAT_PROCESSOR} environment variable (on Sparc Solaris) to one of the following: @table @code @item -2 Use the default configuration (run the program on all available processors) - this is the same as having @code{GNAT_PROCESSOR} unset @item -1 Let the run-time implementation choose one processor and run the program on that processor @item 0 .. Last_Proc Run the program on the specified processor. @code{Last_Proc} is equal to @code{_SC_NPROCESSORS_CONF - 1} (where @code{_SC_NPROCESSORS_CONF} is a system variable). @end table @node Linux-Specific Considerations @section Linux-Specific Considerations @cindex Linux threads libraries @noindent On GNU/Linux without NPTL support (usually system with GNU C Library older than 2.3), the signal model is not POSIX compliant, which means that to send a signal to the process, you need to send the signal to all threads, e.g.@: by using @code{killpg()}. @node AIX-Specific Considerations @section AIX-Specific Considerations @cindex AIX resolver library @noindent On AIX, the resolver library initializes some internal structure on the first call to @code{get*by*} functions, which are used to implement @code{GNAT.Sockets.Get_Host_By_Name} and @code{GNAT.Sockets.Get_Host_By_Address}. If such initialization occurs within an Ada task, and the stack size for the task is the default size, a stack overflow may occur. To avoid this overflow, the user should either ensure that the first call to @code{GNAT.Sockets.Get_Host_By_Name} or @code{GNAT.Sockets.Get_Host_By_Addrss} occurs in the environment task, or use @code{pragma Storage_Size} to specify a sufficiently large size for the stack of the task that contains this call. @node Irix-Specific Considerations @section Irix-Specific Considerations @cindex Irix libraries @noindent The GCC support libraries coming with the Irix compiler have moved to their canonical place with respect to the general Irix ABI related conventions. Running applications built with the default shared GNAT run-time now requires the LD_LIBRARY_PATH environment variable to include this location. A possible way to achieve this is to issue the following command line on a bash prompt: @smallexample @group $ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:`dirname \`gcc --print-file-name=libgcc_s.so\`` @end group @end smallexample @node RTX-Specific Considerations @section RTX-Specific Considerations @cindex RTX libraries @noindent The Real-time Extension (RTX) to Windows is based on the Windows Win32 API. Applications can be built to work in two different modes: @itemize @bullet @item Windows executables that run in Ring 3 to utilize memory protection (@emph{rts-rtx-w32}). @item Real-time subsystem (RTSS) executables that run in Ring 0, where performance can be optimized with RTSS applications taking precedent over all Windows applications (@emph{rts-rtx-rtss}). This mode requires the Microsoft linker to handle RTSS libraries. @end itemize @node HP-UX-Specific Considerations @section HP-UX-Specific Considerations @cindex HP-UX Scheduling @noindent On HP-UX, appropriate privileges are required to change the scheduling parameters of a task. The calling process must have appropriate privileges or be a member of a group having @code{PRIV_RTSCHED} access to successfully change the scheduling parameters. By default, GNAT uses the @code{SCHED_HPUX} policy. To have access to the priority range 0-31 either the @code{FIFO_Within_Priorities} or the @code{Round_Robin_Within_Priorities} scheduling policies need to be set. To specify the @code{FIFO_Within_Priorities} scheduling policy you can use one of the following: @itemize @bullet @item @code{pragma Time_Slice (0.0)} @cindex pragma Time_Slice @item the corresponding binder option @option{-T0} @cindex @option{-T0} option @item @code{pragma Task_Dispatching_Policy (FIFO_Within_Priorities)} @cindex pragma Task_Dispatching_Policy @end itemize @noindent To specify the @code{Round_Robin_Within_Priorities}, scheduling policy you should use @code{pragma Time_Slice} with a value greater than @code{0.0}, or use the corresponding @option{-T} binder option, or set the @code{pragma Task_Dispatching_Policy (Round_Robin_Within_Priorities)}. @c ******************************* @node Example of Binder Output File @appendix Example of Binder Output File @noindent This Appendix displays the source code for @command{gnatbind}'s output file generated for a simple ``Hello World'' program. Comments have been added for clarification purposes. @smallexample @c adanocomment @iftex @leftskip=0cm @end iftex -- The package is called Ada_Main unless this name is actually used -- as a unit name in the partition, in which case some other unique -- name is used. with System; package ada_main is Elab_Final_Code : Integer; pragma Import (C, Elab_Final_Code, "__gnat_inside_elab_final_code"); -- The main program saves the parameters (argument count, -- argument values, environment pointer) in global variables -- for later access by other units including -- Ada.Command_Line. gnat_argc : Integer; gnat_argv : System.Address; gnat_envp : System.Address; -- The actual variables are stored in a library routine. This -- is useful for some shared library situations, where there -- are problems if variables are not in the library. pragma Import (C, gnat_argc); pragma Import (C, gnat_argv); pragma Import (C, gnat_envp); -- The exit status is similarly an external location gnat_exit_status : Integer; pragma Import (C, gnat_exit_status); GNAT_Version : constant String := "GNAT Version: 6.0.0w (20061115)"; pragma Export (C, GNAT_Version, "__gnat_version"); -- This is the generated adafinal routine that performs -- finalization at the end of execution. In the case where -- Ada is the main program, this main program makes a call -- to adafinal at program termination. procedure adafinal; pragma Export (C, adafinal, "adafinal"); -- This is the generated adainit routine that performs -- initialization at the start of execution. In the case -- where Ada is the main program, this main program makes -- a call to adainit at program startup. procedure adainit; pragma Export (C, adainit, "adainit"); -- This routine is called at the start of execution. It is -- a dummy routine that is used by the debugger to breakpoint -- at the start of execution. procedure Break_Start; pragma Import (C, Break_Start, "__gnat_break_start"); -- This is the actual generated main program (it would be -- suppressed if the no main program switch were used). As -- required by standard system conventions, this program has -- the external name main. function main (argc : Integer; argv : System.Address; envp : System.Address) return Integer; pragma Export (C, main, "main"); -- The following set of constants give the version -- identification values for every unit in the bound -- partition. This identification is computed from all -- dependent semantic units, and corresponds to the -- string that would be returned by use of the -- Body_Version or Version attributes. type Version_32 is mod 2 ** 32; u00001 : constant Version_32 := 16#7880BEB3#; u00002 : constant Version_32 := 16#0D24CBD0#; u00003 : constant Version_32 := 16#3283DBEB#; u00004 : constant Version_32 := 16#2359F9ED#; u00005 : constant Version_32 := 16#664FB847#; u00006 : constant Version_32 := 16#68E803DF#; u00007 : constant Version_32 := 16#5572E604#; u00008 : constant Version_32 := 16#46B173D8#; u00009 : constant Version_32 := 16#156A40CF#; u00010 : constant Version_32 := 16#033DABE0#; u00011 : constant Version_32 := 16#6AB38FEA#; u00012 : constant Version_32 := 16#22B6217D#; u00013 : constant Version_32 := 16#68A22947#; u00014 : constant Version_32 := 16#18CC4A56#; u00015 : constant Version_32 := 16#08258E1B#; u00016 : constant Version_32 := 16#367D5222#; u00017 : constant Version_32 := 16#20C9ECA4#; u00018 : constant Version_32 := 16#50D32CB6#; u00019 : constant Version_32 := 16#39A8BB77#; u00020 : constant Version_32 := 16#5CF8FA2B#; u00021 : constant Version_32 := 16#2F1EB794#; u00022 : constant Version_32 := 16#31AB6444#; u00023 : constant Version_32 := 16#1574B6E9#; u00024 : constant Version_32 := 16#5109C189#; u00025 : constant Version_32 := 16#56D770CD#; u00026 : constant Version_32 := 16#02F9DE3D#; u00027 : constant Version_32 := 16#08AB6B2C#; u00028 : constant Version_32 := 16#3FA37670#; u00029 : constant Version_32 := 16#476457A0#; u00030 : constant Version_32 := 16#731E1B6E#; u00031 : constant Version_32 := 16#23C2E789#; u00032 : constant Version_32 := 16#0F1BD6A1#; u00033 : constant Version_32 := 16#7C25DE96#; u00034 : constant Version_32 := 16#39ADFFA2#; u00035 : constant Version_32 := 16#571DE3E7#; u00036 : constant Version_32 := 16#5EB646AB#; u00037 : constant Version_32 := 16#4249379B#; u00038 : constant Version_32 := 16#0357E00A#; u00039 : constant Version_32 := 16#3784FB72#; u00040 : constant Version_32 := 16#2E723019#; u00041 : constant Version_32 := 16#623358EA#; u00042 : constant Version_32 := 16#107F9465#; u00043 : constant Version_32 := 16#6843F68A#; u00044 : constant Version_32 := 16#63305874#; u00045 : constant Version_32 := 16#31E56CE1#; u00046 : constant Version_32 := 16#02917970#; u00047 : constant Version_32 := 16#6CCBA70E#; u00048 : constant Version_32 := 16#41CD4204#; u00049 : constant Version_32 := 16#572E3F58#; u00050 : constant Version_32 := 16#20729FF5#; u00051 : constant Version_32 := 16#1D4F93E8#; u00052 : constant Version_32 := 16#30B2EC3D#; u00053 : constant Version_32 := 16#34054F96#; u00054 : constant Version_32 := 16#5A199860#; u00055 : constant Version_32 := 16#0E7F912B#; u00056 : constant Version_32 := 16#5760634A#; u00057 : constant Version_32 := 16#5D851835#; -- The following Export pragmas export the version numbers -- with symbolic names ending in B (for body) or S -- (for spec) so that they can be located in a link. The -- information provided here is sufficient to track down -- the exact versions of units used in a given build. pragma Export (C, u00001, "helloB"); pragma Export (C, u00002, "system__standard_libraryB"); pragma Export (C, u00003, "system__standard_libraryS"); pragma Export (C, u00004, "adaS"); pragma Export (C, u00005, "ada__text_ioB"); pragma Export (C, u00006, "ada__text_ioS"); pragma Export (C, u00007, "ada__exceptionsB"); pragma Export (C, u00008, "ada__exceptionsS"); pragma Export (C, u00009, "gnatS"); pragma Export (C, u00010, "gnat__heap_sort_aB"); pragma Export (C, u00011, "gnat__heap_sort_aS"); pragma Export (C, u00012, "systemS"); pragma Export (C, u00013, "system__exception_tableB"); pragma Export (C, u00014, "system__exception_tableS"); pragma Export (C, u00015, "gnat__htableB"); pragma Export (C, u00016, "gnat__htableS"); pragma Export (C, u00017, "system__exceptionsS"); pragma Export (C, u00018, "system__machine_state_operationsB"); pragma Export (C, u00019, "system__machine_state_operationsS"); pragma Export (C, u00020, "system__machine_codeS"); pragma Export (C, u00021, "system__storage_elementsB"); pragma Export (C, u00022, "system__storage_elementsS"); pragma Export (C, u00023, "system__secondary_stackB"); pragma Export (C, u00024, "system__secondary_stackS"); pragma Export (C, u00025, "system__parametersB"); pragma Export (C, u00026, "system__parametersS"); pragma Export (C, u00027, "system__soft_linksB"); pragma Export (C, u00028, "system__soft_linksS"); pragma Export (C, u00029, "system__stack_checkingB"); pragma Export (C, u00030, "system__stack_checkingS"); pragma Export (C, u00031, "system__tracebackB"); pragma Export (C, u00032, "system__tracebackS"); pragma Export (C, u00033, "ada__streamsS"); pragma Export (C, u00034, "ada__tagsB"); pragma Export (C, u00035, "ada__tagsS"); pragma Export (C, u00036, "system__string_opsB"); pragma Export (C, u00037, "system__string_opsS"); pragma Export (C, u00038, "interfacesS"); pragma Export (C, u00039, "interfaces__c_streamsB"); pragma Export (C, u00040, "interfaces__c_streamsS"); pragma Export (C, u00041, "system__file_ioB"); pragma Export (C, u00042, "system__file_ioS"); pragma Export (C, u00043, "ada__finalizationB"); pragma Export (C, u00044, "ada__finalizationS"); pragma Export (C, u00045, "system__finalization_rootB"); pragma Export (C, u00046, "system__finalization_rootS"); pragma Export (C, u00047, "system__finalization_implementationB"); pragma Export (C, u00048, "system__finalization_implementationS"); pragma Export (C, u00049, "system__string_ops_concat_3B"); pragma Export (C, u00050, "system__string_ops_concat_3S"); pragma Export (C, u00051, "system__stream_attributesB"); pragma Export (C, u00052, "system__stream_attributesS"); pragma Export (C, u00053, "ada__io_exceptionsS"); pragma Export (C, u00054, "system__unsigned_typesS"); pragma Export (C, u00055, "system__file_control_blockS"); pragma Export (C, u00056, "ada__finalization__list_controllerB"); pragma Export (C, u00057, "ada__finalization__list_controllerS"); -- BEGIN ELABORATION ORDER -- ada (spec) -- gnat (spec) -- gnat.heap_sort_a (spec) -- gnat.heap_sort_a (body) -- gnat.htable (spec) -- gnat.htable (body) -- interfaces (spec) -- system (spec) -- system.machine_code (spec) -- system.parameters (spec) -- system.parameters (body) -- interfaces.c_streams (spec) -- interfaces.c_streams (body) -- system.standard_library (spec) -- ada.exceptions (spec) -- system.exception_table (spec) -- system.exception_table (body) -- ada.io_exceptions (spec) -- system.exceptions (spec) -- system.storage_elements (spec) -- system.storage_elements (body) -- system.machine_state_operations (spec) -- system.machine_state_operations (body) -- system.secondary_stack (spec) -- system.stack_checking (spec) -- system.soft_links (spec) -- system.soft_links (body) -- system.stack_checking (body) -- system.secondary_stack (body) -- system.standard_library (body) -- system.string_ops (spec) -- system.string_ops (body) -- ada.tags (spec) -- ada.tags (body) -- ada.streams (spec) -- system.finalization_root (spec) -- system.finalization_root (body) -- system.string_ops_concat_3 (spec) -- system.string_ops_concat_3 (body) -- system.traceback (spec) -- system.traceback (body) -- ada.exceptions (body) -- system.unsigned_types (spec) -- system.stream_attributes (spec) -- system.stream_attributes (body) -- system.finalization_implementation (spec) -- system.finalization_implementation (body) -- ada.finalization (spec) -- ada.finalization (body) -- ada.finalization.list_controller (spec) -- ada.finalization.list_controller (body) -- system.file_control_block (spec) -- system.file_io (spec) -- system.file_io (body) -- ada.text_io (spec) -- ada.text_io (body) -- hello (body) -- END ELABORATION ORDER end ada_main; -- The following source file name pragmas allow the generated file -- names to be unique for different main programs. They are needed -- since the package name will always be Ada_Main. pragma Source_File_Name (ada_main, Spec_File_Name => "b~hello.ads"); pragma Source_File_Name (ada_main, Body_File_Name => "b~hello.adb"); -- Generated package body for Ada_Main starts here package body ada_main is -- The actual finalization is performed by calling the -- library routine in System.Standard_Library.Adafinal procedure Do_Finalize; pragma Import (C, Do_Finalize, "system__standard_library__adafinal"); ------------- -- adainit -- ------------- @findex adainit procedure adainit is -- These booleans are set to True once the associated unit has -- been elaborated. It is also used to avoid elaborating the -- same unit twice. E040 : Boolean; pragma Import (Ada, E040, "interfaces__c_streams_E"); E008 : Boolean; pragma Import (Ada, E008, "ada__exceptions_E"); E014 : Boolean; pragma Import (Ada, E014, "system__exception_table_E"); E053 : Boolean; pragma Import (Ada, E053, "ada__io_exceptions_E"); E017 : Boolean; pragma Import (Ada, E017, "system__exceptions_E"); E024 : Boolean; pragma Import (Ada, E024, "system__secondary_stack_E"); E030 : Boolean; pragma Import (Ada, E030, "system__stack_checking_E"); E028 : Boolean; pragma Import (Ada, E028, "system__soft_links_E"); E035 : Boolean; pragma Import (Ada, E035, "ada__tags_E"); E033 : Boolean; pragma Import (Ada, E033, "ada__streams_E"); E046 : Boolean; pragma Import (Ada, E046, "system__finalization_root_E"); E048 : Boolean; pragma Import (Ada, E048, "system__finalization_implementation_E"); E044 : Boolean; pragma Import (Ada, E044, "ada__finalization_E"); E057 : Boolean; pragma Import (Ada, E057, "ada__finalization__list_controller_E"); E055 : Boolean; pragma Import (Ada, E055, "system__file_control_block_E"); E042 : Boolean; pragma Import (Ada, E042, "system__file_io_E"); E006 : Boolean; pragma Import (Ada, E006, "ada__text_io_E"); -- Set_Globals is a library routine that stores away the -- value of the indicated set of global values in global -- variables within the library. procedure Set_Globals (Main_Priority : Integer; Time_Slice_Value : Integer; WC_Encoding : Character; Locking_Policy : Character; Queuing_Policy : Character; Task_Dispatching_Policy : Character; Adafinal : System.Address; Unreserve_All_Interrupts : Integer; Exception_Tracebacks : Integer); @findex __gnat_set_globals pragma Import (C, Set_Globals, "__gnat_set_globals"); -- SDP_Table_Build is a library routine used to build the -- exception tables. See unit Ada.Exceptions in files -- a-except.ads/adb for full details of how zero cost -- exception handling works. This procedure, the call to -- it, and the two following tables are all omitted if the -- build is in longjmp/setjmp exception mode. @findex SDP_Table_Build @findex Zero Cost Exceptions procedure SDP_Table_Build (SDP_Addresses : System.Address; SDP_Count : Natural; Elab_Addresses : System.Address; Elab_Addr_Count : Natural); pragma Import (C, SDP_Table_Build, "__gnat_SDP_Table_Build"); -- Table of Unit_Exception_Table addresses. Used for zero -- cost exception handling to build the top level table. ST : aliased constant array (1 .. 23) of System.Address := ( Hello'UET_Address, Ada.Text_Io'UET_Address, Ada.Exceptions'UET_Address, Gnat.Heap_Sort_A'UET_Address, System.Exception_Table'UET_Address, System.Machine_State_Operations'UET_Address, System.Secondary_Stack'UET_Address, System.Parameters'UET_Address, System.Soft_Links'UET_Address, System.Stack_Checking'UET_Address, System.Traceback'UET_Address, Ada.Streams'UET_Address, Ada.Tags'UET_Address, System.String_Ops'UET_Address, Interfaces.C_Streams'UET_Address, System.File_Io'UET_Address, Ada.Finalization'UET_Address, System.Finalization_Root'UET_Address, System.Finalization_Implementation'UET_Address, System.String_Ops_Concat_3'UET_Address, System.Stream_Attributes'UET_Address, System.File_Control_Block'UET_Address, Ada.Finalization.List_Controller'UET_Address); -- Table of addresses of elaboration routines. Used for -- zero cost exception handling to make sure these -- addresses are included in the top level procedure -- address table. EA : aliased constant array (1 .. 23) of System.Address := ( adainit'Code_Address, Do_Finalize'Code_Address, Ada.Exceptions'Elab_Spec'Address, System.Exceptions'Elab_Spec'Address, Interfaces.C_Streams'Elab_Spec'Address, System.Exception_Table'Elab_Body'Address, Ada.Io_Exceptions'Elab_Spec'Address, System.Stack_Checking'Elab_Spec'Address, System.Soft_Links'Elab_Body'Address, System.Secondary_Stack'Elab_Body'Address, Ada.Tags'Elab_Spec'Address, Ada.Tags'Elab_Body'Address, Ada.Streams'Elab_Spec'Address, System.Finalization_Root'Elab_Spec'Address, Ada.Exceptions'Elab_Body'Address, System.Finalization_Implementation'Elab_Spec'Address, System.Finalization_Implementation'Elab_Body'Address, Ada.Finalization'Elab_Spec'Address, Ada.Finalization.List_Controller'Elab_Spec'Address, System.File_Control_Block'Elab_Spec'Address, System.File_Io'Elab_Body'Address, Ada.Text_Io'Elab_Spec'Address, Ada.Text_Io'Elab_Body'Address); -- Start of processing for adainit begin -- Call SDP_Table_Build to build the top level procedure -- table for zero cost exception handling (omitted in -- longjmp/setjmp mode). SDP_Table_Build (ST'Address, 23, EA'Address, 23); -- Call Set_Globals to record various information for -- this partition. The values are derived by the binder -- from information stored in the ali files by the compiler. @findex __gnat_set_globals Set_Globals (Main_Priority => -1, -- Priority of main program, -1 if no pragma Priority used Time_Slice_Value => -1, -- Time slice from Time_Slice pragma, -1 if none used WC_Encoding => 'b', -- Wide_Character encoding used, default is brackets Locking_Policy => ' ', -- Locking_Policy used, default of space means not -- specified, otherwise it is the first character of -- the policy name. Queuing_Policy => ' ', -- Queuing_Policy used, default of space means not -- specified, otherwise it is the first character of -- the policy name. Task_Dispatching_Policy => ' ', -- Task_Dispatching_Policy used, default of space means -- not specified, otherwise first character of the -- policy name. Adafinal => System.Null_Address, -- Address of Adafinal routine, not used anymore Unreserve_All_Interrupts => 0, -- Set true if pragma Unreserve_All_Interrupts was used Exception_Tracebacks => 0); -- Indicates if exception tracebacks are enabled Elab_Final_Code := 1; -- Now we have the elaboration calls for all units in the partition. -- The Elab_Spec and Elab_Body attributes generate references to the -- implicit elaboration procedures generated by the compiler for -- each unit that requires elaboration. if not E040 then Interfaces.C_Streams'Elab_Spec; end if; E040 := True; if not E008 then Ada.Exceptions'Elab_Spec; end if; if not E014 then System.Exception_Table'Elab_Body; E014 := True; end if; if not E053 then Ada.Io_Exceptions'Elab_Spec; E053 := True; end if; if not E017 then System.Exceptions'Elab_Spec; E017 := True; end if; if not E030 then System.Stack_Checking'Elab_Spec; end if; if not E028 then System.Soft_Links'Elab_Body; E028 := True; end if; E030 := True; if not E024 then System.Secondary_Stack'Elab_Body; E024 := True; end if; if not E035 then Ada.Tags'Elab_Spec; end if; if not E035 then Ada.Tags'Elab_Body; E035 := True; end if; if not E033 then Ada.Streams'Elab_Spec; E033 := True; end if; if not E046 then System.Finalization_Root'Elab_Spec; end if; E046 := True; if not E008 then Ada.Exceptions'Elab_Body; E008 := True; end if; if not E048 then System.Finalization_Implementation'Elab_Spec; end if; if not E048 then System.Finalization_Implementation'Elab_Body; E048 := True; end if; if not E044 then Ada.Finalization'Elab_Spec; end if; E044 := True; if not E057 then Ada.Finalization.List_Controller'Elab_Spec; end if; E057 := True; if not E055 then System.File_Control_Block'Elab_Spec; E055 := True; end if; if not E042 then System.File_Io'Elab_Body; E042 := True; end if; if not E006 then Ada.Text_Io'Elab_Spec; end if; if not E006 then Ada.Text_Io'Elab_Body; E006 := True; end if; Elab_Final_Code := 0; end adainit; -------------- -- adafinal -- -------------- @findex adafinal procedure adafinal is begin Do_Finalize; end adafinal; ---------- -- main -- ---------- -- main is actually a function, as in the ANSI C standard, -- defined to return the exit status. The three parameters -- are the argument count, argument values and environment -- pointer. @findex Main Program function main (argc : Integer; argv : System.Address; envp : System.Address) return Integer is -- The initialize routine performs low level system -- initialization using a standard library routine which -- sets up signal handling and performs any other -- required setup. The routine can be found in file -- a-init.c. @findex __gnat_initialize procedure initialize; pragma Import (C, initialize, "__gnat_initialize"); -- The finalize routine performs low level system -- finalization using a standard library routine. The -- routine is found in file a-final.c and in the standard -- distribution is a dummy routine that does nothing, so -- really this is a hook for special user finalization. @findex __gnat_finalize procedure finalize; pragma Import (C, finalize, "__gnat_finalize"); -- We get to the main program of the partition by using -- pragma Import because if we try to with the unit and -- call it Ada style, then not only do we waste time -- recompiling it, but also, we don't really know the right -- switches (e.g.@: identifier character set) to be used -- to compile it. procedure Ada_Main_Program; pragma Import (Ada, Ada_Main_Program, "_ada_hello"); -- Start of processing for main begin -- Save global variables gnat_argc := argc; gnat_argv := argv; gnat_envp := envp; -- Call low level system initialization Initialize; -- Call our generated Ada initialization routine adainit; -- This is the point at which we want the debugger to get -- control Break_Start; -- Now we call the main program of the partition Ada_Main_Program; -- Perform Ada finalization adafinal; -- Perform low level system finalization Finalize; -- Return the proper exit status return (gnat_exit_status); end; -- This section is entirely comments, so it has no effect on the -- compilation of the Ada_Main package. It provides the list of -- object files and linker options, as well as some standard -- libraries needed for the link. The gnatlink utility parses -- this b~hello.adb file to read these comment lines to generate -- the appropriate command line arguments for the call to the -- system linker. The BEGIN/END lines are used for sentinels for -- this parsing operation. -- The exact file names will of course depend on the environment, -- host/target and location of files on the host system. @findex Object file list -- BEGIN Object file/option list -- ./hello.o -- -L./ -- -L/usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/ -- /usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/libgnat.a -- END Object file/option list end ada_main; @end smallexample @noindent The Ada code in the above example is exactly what is generated by the binder. We have added comments to more clearly indicate the function of each part of the generated @code{Ada_Main} package. The code is standard Ada in all respects, and can be processed by any tools that handle Ada. In particular, it is possible to use the debugger in Ada mode to debug the generated @code{Ada_Main} package. For example, suppose that for reasons that you do not understand, your program is crashing during elaboration of the body of @code{Ada.Text_IO}. To locate this bug, you can place a breakpoint on the call: @smallexample @c ada Ada.Text_Io'Elab_Body; @end smallexample @noindent and trace the elaboration routine for this package to find out where the problem might be (more usually of course you would be debugging elaboration code in your own application). @node Elaboration Order Handling in GNAT @appendix Elaboration Order Handling in GNAT @cindex Order of elaboration @cindex Elaboration control @menu * Elaboration Code:: * Checking the Elaboration Order:: * Controlling the Elaboration Order:: * Controlling Elaboration in GNAT - Internal Calls:: * Controlling Elaboration in GNAT - External Calls:: * Default Behavior in GNAT - Ensuring Safety:: * Treatment of Pragma Elaborate:: * Elaboration Issues for Library Tasks:: * Mixing Elaboration Models:: * What to Do If the Default Elaboration Behavior Fails:: * Elaboration for Access-to-Subprogram Values:: * Summary of Procedures for Elaboration Control:: * Other Elaboration Order Considerations:: @end menu @noindent This chapter describes the handling of elaboration code in Ada and in GNAT, and discusses how the order of elaboration of program units can be controlled in GNAT, either automatically or with explicit programming features. @node Elaboration Code @section Elaboration Code @noindent Ada provides rather general mechanisms for executing code at elaboration time, that is to say before the main program starts executing. Such code arises in three contexts: @table @asis @item Initializers for variables. Variables declared at the library level, in package specs or bodies, can require initialization that is performed at elaboration time, as in: @smallexample @c ada @cartouche Sqrt_Half : Float := Sqrt (0.5); @end cartouche @end smallexample @item Package initialization code Code in a @code{BEGIN-END} section at the outer level of a package body is executed as part of the package body elaboration code. @item Library level task allocators Tasks that are declared using task allocators at the library level start executing immediately and hence can execute at elaboration time. @end table @noindent Subprogram calls are possible in any of these contexts, which means that any arbitrary part of the program may be executed as part of the elaboration code. It is even possible to write a program which does all its work at elaboration time, with a null main program, although stylistically this would usually be considered an inappropriate way to structure a program. An important concern arises in the context of elaboration code: we have to be sure that it is executed in an appropriate order. What we have is a series of elaboration code sections, potentially one section for each unit in the program. It is important that these execute in the correct order. Correctness here means that, taking the above example of the declaration of @code{Sqrt_Half}, if some other piece of elaboration code references @code{Sqrt_Half}, then it must run after the section of elaboration code that contains the declaration of @code{Sqrt_Half}. There would never be any order of elaboration problem if we made a rule that whenever you @code{with} a unit, you must elaborate both the spec and body of that unit before elaborating the unit doing the @code{with}'ing: @smallexample @c ada @group @cartouche with Unit_1; package Unit_2 is @dots{} @end cartouche @end group @end smallexample @noindent would require that both the body and spec of @code{Unit_1} be elaborated before the spec of @code{Unit_2}. However, a rule like that would be far too restrictive. In particular, it would make it impossible to have routines in separate packages that were mutually recursive. You might think that a clever enough compiler could look at the actual elaboration code and determine an appropriate correct order of elaboration, but in the general case, this is not possible. Consider the following example. In the body of @code{Unit_1}, we have a procedure @code{Func_1} that references the variable @code{Sqrt_1}, which is declared in the elaboration code of the body of @code{Unit_1}: @smallexample @c ada @cartouche Sqrt_1 : Float := Sqrt (0.1); @end cartouche @end smallexample @noindent The elaboration code of the body of @code{Unit_1} also contains: @smallexample @c ada @group @cartouche if expression_1 = 1 then Q := Unit_2.Func_2; end if; @end cartouche @end group @end smallexample @noindent @code{Unit_2} is exactly parallel, it has a procedure @code{Func_2} that references the variable @code{Sqrt_2}, which is declared in the elaboration code of the body @code{Unit_2}: @smallexample @c ada @cartouche Sqrt_2 : Float := Sqrt (0.1); @end cartouche @end smallexample @noindent The elaboration code of the body of @code{Unit_2} also contains: @smallexample @c ada @group @cartouche if expression_2 = 2 then Q := Unit_1.Func_1; end if; @end cartouche @end group @end smallexample @noindent Now the question is, which of the following orders of elaboration is acceptable: @smallexample @group Spec of Unit_1 Spec of Unit_2 Body of Unit_1 Body of Unit_2 @end group @end smallexample @noindent or @smallexample @group Spec of Unit_2 Spec of Unit_1 Body of Unit_2 Body of Unit_1 @end group @end smallexample @noindent If you carefully analyze the flow here, you will see that you cannot tell at compile time the answer to this question. If @code{expression_1} is not equal to 1, and @code{expression_2} is not equal to 2, then either order is acceptable, because neither of the function calls is executed. If both tests evaluate to true, then neither order is acceptable and in fact there is no correct order. If one of the two expressions is true, and the other is false, then one of the above orders is correct, and the other is incorrect. For example, if @code{expression_1} /= 1 and @code{expression_2} = 2, then the call to @code{Func_1} will occur, but not the call to @code{Func_2.} This means that it is essential to elaborate the body of @code{Unit_1} before the body of @code{Unit_2}, so the first order of elaboration is correct and the second is wrong. By making @code{expression_1} and @code{expression_2} depend on input data, or perhaps the time of day, we can make it impossible for the compiler or binder to figure out which of these expressions will be true, and hence it is impossible to guarantee a safe order of elaboration at run time. @node Checking the Elaboration Order @section Checking the Elaboration Order @noindent In some languages that involve the same kind of elaboration problems, e.g.@: Java and C++, the programmer is expected to worry about these ordering problems himself, and it is common to write a program in which an incorrect elaboration order gives surprising results, because it references variables before they are initialized. Ada is designed to be a safe language, and a programmer-beware approach is clearly not sufficient. Consequently, the language provides three lines of defense: @table @asis @item Standard rules Some standard rules restrict the possible choice of elaboration order. In particular, if you @code{with} a unit, then its spec is always elaborated before the unit doing the @code{with}. Similarly, a parent spec is always elaborated before the child spec, and finally a spec is always elaborated before its corresponding body. @item Dynamic elaboration checks @cindex Elaboration checks @cindex Checks, elaboration Dynamic checks are made at run time, so that if some entity is accessed before it is elaborated (typically by means of a subprogram call) then the exception (@code{Program_Error}) is raised. @item Elaboration control Facilities are provided for the programmer to specify the desired order of elaboration. @end table Let's look at these facilities in more detail. First, the rules for dynamic checking. One possible rule would be simply to say that the exception is raised if you access a variable which has not yet been elaborated. The trouble with this approach is that it could require expensive checks on every variable reference. Instead Ada has two rules which are a little more restrictive, but easier to check, and easier to state: @table @asis @item Restrictions on calls A subprogram can only be called at elaboration time if its body has been elaborated. The rules for elaboration given above guarantee that the spec of the subprogram has been elaborated before the call, but not the body. If this rule is violated, then the exception @code{Program_Error} is raised. @item Restrictions on instantiations A generic unit can only be instantiated if the body of the generic unit has been elaborated. Again, the rules for elaboration given above guarantee that the spec of the generic unit has been elaborated before the instantiation, but not the body. If this rule is violated, then the exception @code{Program_Error} is raised. @end table @noindent The idea is that if the body has been elaborated, then any variables it references must have been elaborated; by checking for the body being elaborated we guarantee that none of its references causes any trouble. As we noted above, this is a little too restrictive, because a subprogram that has no non-local references in its body may in fact be safe to call. However, it really would be unsafe to rely on this, because it would mean that the caller was aware of details of the implementation in the body. This goes against the basic tenets of Ada. A plausible implementation can be described as follows. A Boolean variable is associated with each subprogram and each generic unit. This variable is initialized to False, and is set to True at the point body is elaborated. Every call or instantiation checks the variable, and raises @code{Program_Error} if the variable is False. Note that one might think that it would be good enough to have one Boolean variable for each package, but that would not deal with cases of trying to call a body in the same package as the call that has not been elaborated yet. Of course a compiler may be able to do enough analysis to optimize away some of the Boolean variables as unnecessary, and @code{GNAT} indeed does such optimizations, but still the easiest conceptual model is to think of there being one variable per subprogram. @node Controlling the Elaboration Order @section Controlling the Elaboration Order @noindent In the previous section we discussed the rules in Ada which ensure that @code{Program_Error} is raised if an incorrect elaboration order is chosen. This prevents erroneous executions, but we need mechanisms to specify a correct execution and avoid the exception altogether. To achieve this, Ada provides a number of features for controlling the order of elaboration. We discuss these features in this section. First, there are several ways of indicating to the compiler that a given unit has no elaboration problems: @table @asis @item packages that do not require a body A library package that does not require a body does not permit a body (this rule was introduced in Ada 95). Thus if we have a such a package, as in: @smallexample @c ada @group @cartouche package Definitions is generic type m is new integer; package Subp is type a is array (1 .. 10) of m; type b is array (1 .. 20) of m; end Subp; end Definitions; @end cartouche @end group @end smallexample @noindent A package that @code{with}'s @code{Definitions} may safely instantiate @code{Definitions.Subp} because the compiler can determine that there definitely is no package body to worry about in this case @item pragma Pure @cindex pragma Pure @findex Pure Places sufficient restrictions on a unit to guarantee that no call to any subprogram in the unit can result in an elaboration problem. This means that the compiler does not need to worry about the point of elaboration of such units, and in particular, does not need to check any calls to any subprograms in this unit. @item pragma Preelaborate @findex Preelaborate @cindex pragma Preelaborate This pragma places slightly less stringent restrictions on a unit than does pragma Pure, but these restrictions are still sufficient to ensure that there are no elaboration problems with any calls to the unit. @item pragma Elaborate_Body @findex Elaborate_Body @cindex pragma Elaborate_Body This pragma requires that the body of a unit be elaborated immediately after its spec. Suppose a unit @code{A} has such a pragma, and unit @code{B} does a @code{with} of unit @code{A}. Recall that the standard rules require the spec of unit @code{A} to be elaborated before the @code{with}'ing unit; given the pragma in @code{A}, we also know that the body of @code{A} will be elaborated before @code{B}, so that calls to @code{A} are safe and do not need a check. @end table @noindent Note that, unlike pragma @code{Pure} and pragma @code{Preelaborate}, the use of @code{Elaborate_Body} does not guarantee that the program is free of elaboration problems, because it may not be possible to satisfy the requested elaboration order. Let's go back to the example with @code{Unit_1} and @code{Unit_2}. If a programmer marks @code{Unit_1} as @code{Elaborate_Body}, and not @code{Unit_2,} then the order of elaboration will be: @smallexample @group Spec of Unit_2 Spec of Unit_1 Body of Unit_1 Body of Unit_2 @end group @end smallexample @noindent Now that means that the call to @code{Func_1} in @code{Unit_2} need not be checked, it must be safe. But the call to @code{Func_2} in @code{Unit_1} may still fail if @code{Expression_1} is equal to 1, and the programmer must still take responsibility for this not being the case. If all units carry a pragma @code{Elaborate_Body}, then all problems are eliminated, except for calls entirely within a body, which are in any case fully under programmer control. However, using the pragma everywhere is not always possible. In particular, for our @code{Unit_1}/@code{Unit_2} example, if we marked both of them as having pragma @code{Elaborate_Body}, then clearly there would be no possible elaboration order. The above pragmas allow a server to guarantee safe use by clients, and clearly this is the preferable approach. Consequently a good rule is to mark units as @code{Pure} or @code{Preelaborate} if possible, and if this is not possible, mark them as @code{Elaborate_Body} if possible. As we have seen, there are situations where neither of these three pragmas can be used. So we also provide methods for clients to control the order of elaboration of the servers on which they depend: @table @asis @item pragma Elaborate (unit) @findex Elaborate @cindex pragma Elaborate This pragma is placed in the context clause, after a @code{with} clause, and it requires that the body of the named unit be elaborated before the unit in which the pragma occurs. The idea is to use this pragma if the current unit calls at elaboration time, directly or indirectly, some subprogram in the named unit. @item pragma Elaborate_All (unit) @findex Elaborate_All @cindex pragma Elaborate_All This is a stronger version of the Elaborate pragma. Consider the following example: @smallexample Unit A @code{with}'s unit B and calls B.Func in elab code Unit B @code{with}'s unit C, and B.Func calls C.Func @end smallexample @noindent Now if we put a pragma @code{Elaborate (B)} in unit @code{A}, this ensures that the body of @code{B} is elaborated before the call, but not the body of @code{C}, so the call to @code{C.Func} could still cause @code{Program_Error} to be raised. The effect of a pragma @code{Elaborate_All} is stronger, it requires not only that the body of the named unit be elaborated before the unit doing the @code{with}, but also the bodies of all units that the named unit uses, following @code{with} links transitively. For example, if we put a pragma @code{Elaborate_All (B)} in unit @code{A}, then it requires not only that the body of @code{B} be elaborated before @code{A}, but also the body of @code{C}, because @code{B} @code{with}'s @code{C}. @end table @noindent We are now in a position to give a usage rule in Ada for avoiding elaboration problems, at least if dynamic dispatching and access to subprogram values are not used. We will handle these cases separately later. The rule is simple. If a unit has elaboration code that can directly or indirectly make a call to a subprogram in a @code{with}'ed unit, or instantiate a generic package in a @code{with}'ed unit, then if the @code{with}'ed unit does not have pragma @code{Pure} or @code{Preelaborate}, then the client should have a pragma @code{Elaborate_All} for the @code{with}'ed unit. By following this rule a client is assured that calls can be made without risk of an exception. For generic subprogram instantiations, the rule can be relaxed to require only a pragma @code{Elaborate} since elaborating the body of a subprogram cannot cause any transitive elaboration (we are not calling the subprogram in this case, just elaborating its declaration). If this rule is not followed, then a program may be in one of four states: @table @asis @item No order exists No order of elaboration exists which follows the rules, taking into account any @code{Elaborate}, @code{Elaborate_All}, or @code{Elaborate_Body} pragmas. In this case, an Ada compiler must diagnose the situation at bind time, and refuse to build an executable program. @item One or more orders exist, all incorrect One or more acceptable elaboration orders exist, and all of them generate an elaboration order problem. In this case, the binder can build an executable program, but @code{Program_Error} will be raised when the program is run. @item Several orders exist, some right, some incorrect One or more acceptable elaboration orders exists, and some of them work, and some do not. The programmer has not controlled the order of elaboration, so the binder may or may not pick one of the correct orders, and the program may or may not raise an exception when it is run. This is the worst case, because it means that the program may fail when moved to another compiler, or even another version of the same compiler. @item One or more orders exists, all correct One ore more acceptable elaboration orders exist, and all of them work. In this case the program runs successfully. This state of affairs can be guaranteed by following the rule we gave above, but may be true even if the rule is not followed. @end table @noindent Note that one additional advantage of following our rules on the use of @code{Elaborate} and @code{Elaborate_All} is that the program continues to stay in the ideal (all orders OK) state even if maintenance changes some bodies of some units. Conversely, if a program that does not follow this rule happens to be safe at some point, this state of affairs may deteriorate silently as a result of maintenance changes. You may have noticed that the above discussion did not mention the use of @code{Elaborate_Body}. This was a deliberate omission. If you @code{with} an @code{Elaborate_Body} unit, it still may be the case that code in the body makes calls to some other unit, so it is still necessary to use @code{Elaborate_All} on such units. @node Controlling Elaboration in GNAT - Internal Calls @section Controlling Elaboration in GNAT - Internal Calls @noindent In the case of internal calls, i.e., calls within a single package, the programmer has full control over the order of elaboration, and it is up to the programmer to elaborate declarations in an appropriate order. For example writing: @smallexample @c ada @group @cartouche function One return Float; Q : Float := One; function One return Float is begin return 1.0; end One; @end cartouche @end group @end smallexample @noindent will obviously raise @code{Program_Error} at run time, because function One will be called before its body is elaborated. In this case GNAT will generate a warning that the call will raise @code{Program_Error}: @smallexample @group @cartouche 1. procedure y is 2. function One return Float; 3. 4. Q : Float := One; | >>> warning: cannot call "One" before body is elaborated >>> warning: Program_Error will be raised at run time 5. 6. function One return Float is 7. begin 8. return 1.0; 9. end One; 10. 11. begin 12. null; 13. end; @end cartouche @end group @end smallexample @noindent Note that in this particular case, it is likely that the call is safe, because the function @code{One} does not access any global variables. Nevertheless in Ada, we do not want the validity of the check to depend on the contents of the body (think about the separate compilation case), so this is still wrong, as we discussed in the previous sections. The error is easily corrected by rearranging the declarations so that the body of @code{One} appears before the declaration containing the call (note that in Ada 95 and Ada 2005, declarations can appear in any order, so there is no restriction that would prevent this reordering, and if we write: @smallexample @c ada @group @cartouche function One return Float; function One return Float is begin return 1.0; end One; Q : Float := One; @end cartouche @end group @end smallexample @noindent then all is well, no warning is generated, and no @code{Program_Error} exception will be raised. Things are more complicated when a chain of subprograms is executed: @smallexample @c ada @group @cartouche function A return Integer; function B return Integer; function C return Integer; function B return Integer is begin return A; end; function C return Integer is begin return B; end; X : Integer := C; function A return Integer is begin return 1; end; @end cartouche @end group @end smallexample @noindent Now the call to @code{C} at elaboration time in the declaration of @code{X} is correct, because the body of @code{C} is already elaborated, and the call to @code{B} within the body of @code{C} is correct, but the call to @code{A} within the body of @code{B} is incorrect, because the body of @code{A} has not been elaborated, so @code{Program_Error} will be raised on the call to @code{A}. In this case GNAT will generate a warning that @code{Program_Error} may be raised at the point of the call. Let's look at the warning: @smallexample @group @cartouche 1. procedure x is 2. function A return Integer; 3. function B return Integer; 4. function C return Integer; 5. 6. function B return Integer is begin return A; end; | >>> warning: call to "A" before body is elaborated may raise Program_Error >>> warning: "B" called at line 7 >>> warning: "C" called at line 9 7. function C return Integer is begin return B; end; 8. 9. X : Integer := C; 10. 11. function A return Integer is begin return 1; end; 12. 13. begin 14. null; 15. end; @end cartouche @end group @end smallexample @noindent Note that the message here says ``may raise'', instead of the direct case, where the message says ``will be raised''. That's because whether @code{A} is actually called depends in general on run-time flow of control. For example, if the body of @code{B} said @smallexample @c ada @group @cartouche function B return Integer is begin if some-condition-depending-on-input-data then return A; else return 1; end if; end B; @end cartouche @end group @end smallexample @noindent then we could not know until run time whether the incorrect call to A would actually occur, so @code{Program_Error} might or might not be raised. It is possible for a compiler to do a better job of analyzing bodies, to determine whether or not @code{Program_Error} might be raised, but it certainly couldn't do a perfect job (that would require solving the halting problem and is provably impossible), and because this is a warning anyway, it does not seem worth the effort to do the analysis. Cases in which it would be relevant are rare. In practice, warnings of either of the forms given above will usually correspond to real errors, and should be examined carefully and eliminated. In the rare case where a warning is bogus, it can be suppressed by any of the following methods: @itemize @bullet @item Compile with the @option{-gnatws} switch set @item Suppress @code{Elaboration_Check} for the called subprogram @item Use pragma @code{Warnings_Off} to turn warnings off for the call @end itemize @noindent For the internal elaboration check case, GNAT by default generates the necessary run-time checks to ensure that @code{Program_Error} is raised if any call fails an elaboration check. Of course this can only happen if a warning has been issued as described above. The use of pragma @code{Suppress (Elaboration_Check)} may (but is not guaranteed to) suppress some of these checks, meaning that it may be possible (but is not guaranteed) for a program to be able to call a subprogram whose body is not yet elaborated, without raising a @code{Program_Error} exception. @node Controlling Elaboration in GNAT - External Calls @section Controlling Elaboration in GNAT - External Calls @noindent The previous section discussed the case in which the execution of a particular thread of elaboration code occurred entirely within a single unit. This is the easy case to handle, because a programmer has direct and total control over the order of elaboration, and furthermore, checks need only be generated in cases which are rare and which the compiler can easily detect. The situation is more complex when separate compilation is taken into account. Consider the following: @smallexample @c ada @cartouche @group package Math is function Sqrt (Arg : Float) return Float; end Math; package body Math is function Sqrt (Arg : Float) return Float is begin @dots{} end Sqrt; end Math; @end group @group with Math; package Stuff is X : Float := Math.Sqrt (0.5); end Stuff; with Stuff; procedure Main is begin @dots{} end Main; @end group @end cartouche @end smallexample @noindent where @code{Main} is the main program. When this program is executed, the elaboration code must first be executed, and one of the jobs of the binder is to determine the order in which the units of a program are to be elaborated. In this case we have four units: the spec and body of @code{Math}, the spec of @code{Stuff} and the body of @code{Main}). In what order should the four separate sections of elaboration code be executed? There are some restrictions in the order of elaboration that the binder can choose. In particular, if unit U has a @code{with} for a package @code{X}, then you are assured that the spec of @code{X} is elaborated before U , but you are not assured that the body of @code{X} is elaborated before U. This means that in the above case, the binder is allowed to choose the order: @smallexample spec of Math spec of Stuff body of Math body of Main @end smallexample @noindent but that's not good, because now the call to @code{Math.Sqrt} that happens during the elaboration of the @code{Stuff} spec happens before the body of @code{Math.Sqrt} is elaborated, and hence causes @code{Program_Error} exception to be raised. At first glance, one might say that the binder is misbehaving, because obviously you want to elaborate the body of something you @code{with} first, but that is not a general rule that can be followed in all cases. Consider @smallexample @c ada @group @cartouche package X is @dots{} package Y is @dots{} with X; package body Y is @dots{} with Y; package body X is @dots{} @end cartouche @end group @end smallexample @noindent This is a common arrangement, and, apart from the order of elaboration problems that might arise in connection with elaboration code, this works fine. A rule that says that you must first elaborate the body of anything you @code{with} cannot work in this case: the body of @code{X} @code{with}'s @code{Y}, which means you would have to elaborate the body of @code{Y} first, but that @code{with}'s @code{X}, which means you have to elaborate the body of @code{X} first, but @dots{} and we have a loop that cannot be broken. It is true that the binder can in many cases guess an order of elaboration that is unlikely to cause a @code{Program_Error} exception to be raised, and it tries to do so (in the above example of @code{Math/Stuff/Spec}, the GNAT binder will by default elaborate the body of @code{Math} right after its spec, so all will be well). However, a program that blindly relies on the binder to be helpful can get into trouble, as we discussed in the previous sections, so GNAT provides a number of facilities for assisting the programmer in developing programs that are robust with respect to elaboration order. @node Default Behavior in GNAT - Ensuring Safety @section Default Behavior in GNAT - Ensuring Safety @noindent The default behavior in GNAT ensures elaboration safety. In its default mode GNAT implements the rule we previously described as the right approach. Let's restate it: @itemize @item @emph{If a unit has elaboration code that can directly or indirectly make a call to a subprogram in a @code{with}'ed unit, or instantiate a generic package in a @code{with}'ed unit, then if the @code{with}'ed unit does not have pragma @code{Pure} or @code{Preelaborate}, then the client should have an @code{Elaborate_All} pragma for the @code{with}'ed unit.} @emph{In the case of instantiating a generic subprogram, it is always sufficient to have only an @code{Elaborate} pragma for the @code{with}'ed unit.} @end itemize @noindent By following this rule a client is assured that calls and instantiations can be made without risk of an exception. In this mode GNAT traces all calls that are potentially made from elaboration code, and puts in any missing implicit @code{Elaborate} and @code{Elaborate_All} pragmas. The advantage of this approach is that no elaboration problems are possible if the binder can find an elaboration order that is consistent with these implicit @code{Elaborate} and @code{Elaborate_All} pragmas. The disadvantage of this approach is that no such order may exist. If the binder does not generate any diagnostics, then it means that it has found an elaboration order that is guaranteed to be safe. However, the binder may still be relying on implicitly generated @code{Elaborate} and @code{Elaborate_All} pragmas so portability to other compilers than GNAT is not guaranteed. If it is important to guarantee portability, then the compilations should use the @option{-gnatwl} (warn on elaboration problems) switch. This will cause warning messages to be generated indicating the missing @code{Elaborate} and @code{Elaborate_All} pragmas. Consider the following source program: @smallexample @c ada @group @cartouche with k; package j is m : integer := k.r; end; @end cartouche @end group @end smallexample @noindent where it is clear that there should be a pragma @code{Elaborate_All} for unit @code{k}. An implicit pragma will be generated, and it is likely that the binder will be able to honor it. However, if you want to port this program to some other Ada compiler than GNAT. it is safer to include the pragma explicitly in the source. If this unit is compiled with the @option{-gnatwl} switch, then the compiler outputs a warning: @smallexample @group @cartouche 1. with k; 2. package j is 3. m : integer := k.r; | >>> warning: call to "r" may raise Program_Error >>> warning: missing pragma Elaborate_All for "k" 4. end; @end cartouche @end group @end smallexample @noindent and these warnings can be used as a guide for supplying manually the missing pragmas. It is usually a bad idea to use this warning option during development. That's because it will warn you when you need to put in a pragma, but cannot warn you when it is time to take it out. So the use of pragma @code{Elaborate_All} may lead to unnecessary dependencies and even false circularities. This default mode is more restrictive than the Ada Reference Manual, and it is possible to construct programs which will compile using the dynamic model described there, but will run into a circularity using the safer static model we have described. Of course any Ada compiler must be able to operate in a mode consistent with the requirements of the Ada Reference Manual, and in particular must have the capability of implementing the standard dynamic model of elaboration with run-time checks. In GNAT, this standard mode can be achieved either by the use of the @option{-gnatE} switch on the compiler (@command{gcc} or @command{gnatmake}) command, or by the use of the configuration pragma: @smallexample @c ada pragma Elaboration_Checks (DYNAMIC); @end smallexample @noindent Either approach will cause the unit affected to be compiled using the standard dynamic run-time elaboration checks described in the Ada Reference Manual. The static model is generally preferable, since it is clearly safer to rely on compile and link time checks rather than run-time checks. However, in the case of legacy code, it may be difficult to meet the requirements of the static model. This issue is further discussed in @ref{What to Do If the Default Elaboration Behavior Fails}. Note that the static model provides a strict subset of the allowed behavior and programs of the Ada Reference Manual, so if you do adhere to the static model and no circularities exist, then you are assured that your program will work using the dynamic model, providing that you remove any pragma Elaborate statements from the source. @node Treatment of Pragma Elaborate @section Treatment of Pragma Elaborate @cindex Pragma Elaborate @noindent The use of @code{pragma Elaborate} should generally be avoided in Ada 95 and Ada 2005 programs, since there is no guarantee that transitive calls will be properly handled. Indeed at one point, this pragma was placed in Annex J (Obsolescent Features), on the grounds that it is never useful. Now that's a bit restrictive. In practice, the case in which @code{pragma Elaborate} is useful is when the caller knows that there are no transitive calls, or that the called unit contains all necessary transitive @code{pragma Elaborate} statements, and legacy code often contains such uses. Strictly speaking the static mode in GNAT should ignore such pragmas, since there is no assurance at compile time that the necessary safety conditions are met. In practice, this would cause GNAT to be incompatible with correctly written Ada 83 code that had all necessary @code{pragma Elaborate} statements in place. Consequently, we made the decision that GNAT in its default mode will believe that if it encounters a @code{pragma Elaborate} then the programmer knows what they are doing, and it will trust that no elaboration errors can occur. The result of this decision is two-fold. First to be safe using the static mode, you should remove all @code{pragma Elaborate} statements. Second, when fixing circularities in existing code, you can selectively use @code{pragma Elaborate} statements to convince the static mode of GNAT that it need not generate an implicit @code{pragma Elaborate_All} statement. When using the static mode with @option{-gnatwl}, any use of @code{pragma Elaborate} will generate a warning about possible problems. @node Elaboration Issues for Library Tasks @section Elaboration Issues for Library Tasks @cindex Library tasks, elaboration issues @cindex Elaboration of library tasks @noindent In this section we examine special elaboration issues that arise for programs that declare library level tasks. Generally the model of execution of an Ada program is that all units are elaborated, and then execution of the program starts. However, the declaration of library tasks definitely does not fit this model. The reason for this is that library tasks start as soon as they are declared (more precisely, as soon as the statement part of the enclosing package body is reached), that is to say before elaboration of the program is complete. This means that if such a task calls a subprogram, or an entry in another task, the callee may or may not be elaborated yet, and in the standard Reference Manual model of dynamic elaboration checks, you can even get timing dependent Program_Error exceptions, since there can be a race between the elaboration code and the task code. The static model of elaboration in GNAT seeks to avoid all such dynamic behavior, by being conservative, and the conservative approach in this particular case is to assume that all the code in a task body is potentially executed at elaboration time if a task is declared at the library level. This can definitely result in unexpected circularities. Consider the following example @smallexample @c ada package Decls is task Lib_Task is entry Start; end Lib_Task; type My_Int is new Integer; function Ident (M : My_Int) return My_Int; end Decls; with Utils; package body Decls is task body Lib_Task is begin accept Start; Utils.Put_Val (2); end Lib_Task; function Ident (M : My_Int) return My_Int is begin return M; end Ident; end Decls; with Decls; package Utils is procedure Put_Val (Arg : Decls.My_Int); end Utils; with Text_IO; package body Utils is procedure Put_Val (Arg : Decls.My_Int) is begin Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg))); end Put_Val; end Utils; with Decls; procedure Main is begin Decls.Lib_Task.Start; end; @end smallexample @noindent If the above example is compiled in the default static elaboration mode, then a circularity occurs. The circularity comes from the call @code{Utils.Put_Val} in the task body of @code{Decls.Lib_Task}. Since this call occurs in elaboration code, we need an implicit pragma @code{Elaborate_All} for @code{Utils}. This means that not only must the spec and body of @code{Utils} be elaborated before the body of @code{Decls}, but also the spec and body of any unit that is @code{with'ed} by the body of @code{Utils} must also be elaborated before the body of @code{Decls}. This is the transitive implication of pragma @code{Elaborate_All} and it makes sense, because in general the body of @code{Put_Val} might have a call to something in a @code{with'ed} unit. In this case, the body of Utils (actually its spec) @code{with's} @code{Decls}. Unfortunately this means that the body of @code{Decls} must be elaborated before itself, in case there is a call from the body of @code{Utils}. Here is the exact chain of events we are worrying about: @enumerate @item In the body of @code{Decls} a call is made from within the body of a library task to a subprogram in the package @code{Utils}. Since this call may occur at elaboration time (given that the task is activated at elaboration time), we have to assume the worst, i.e., that the call does happen at elaboration time. @item This means that the body and spec of @code{Util} must be elaborated before the body of @code{Decls} so that this call does not cause an access before elaboration. @item Within the body of @code{Util}, specifically within the body of @code{Util.Put_Val} there may be calls to any unit @code{with}'ed by this package. @item One such @code{with}'ed package is package @code{Decls}, so there might be a call to a subprogram in @code{Decls} in @code{Put_Val}. In fact there is such a call in this example, but we would have to assume that there was such a call even if it were not there, since we are not supposed to write the body of @code{Decls} knowing what is in the body of @code{Utils}; certainly in the case of the static elaboration model, the compiler does not know what is in other bodies and must assume the worst. @item This means that the spec and body of @code{Decls} must also be elaborated before we elaborate the unit containing the call, but that unit is @code{Decls}! This means that the body of @code{Decls} must be elaborated before itself, and that's a circularity. @end enumerate @noindent Indeed, if you add an explicit pragma @code{Elaborate_All} for @code{Utils} in the body of @code{Decls} you will get a true Ada Reference Manual circularity that makes the program illegal. In practice, we have found that problems with the static model of elaboration in existing code often arise from library tasks, so we must address this particular situation. Note that if we compile and run the program above, using the dynamic model of elaboration (that is to say use the @option{-gnatE} switch), then it compiles, binds, links, and runs, printing the expected result of 2. Therefore in some sense the circularity here is only apparent, and we need to capture the properties of this program that distinguish it from other library-level tasks that have real elaboration problems. We have four possible answers to this question: @itemize @bullet @item Use the dynamic model of elaboration. If we use the @option{-gnatE} switch, then as noted above, the program works. Why is this? If we examine the task body, it is apparent that the task cannot proceed past the @code{accept} statement until after elaboration has been completed, because the corresponding entry call comes from the main program, not earlier. This is why the dynamic model works here. But that's really giving up on a precise analysis, and we prefer to take this approach only if we cannot solve the problem in any other manner. So let us examine two ways to reorganize the program to avoid the potential elaboration problem. @item Split library tasks into separate packages. Write separate packages, so that library tasks are isolated from other declarations as much as possible. Let us look at a variation on the above program. @smallexample @c ada package Decls1 is task Lib_Task is entry Start; end Lib_Task; end Decls1; with Utils; package body Decls1 is task body Lib_Task is begin accept Start; Utils.Put_Val (2); end Lib_Task; end Decls1; package Decls2 is type My_Int is new Integer; function Ident (M : My_Int) return My_Int; end Decls2; with Utils; package body Decls2 is function Ident (M : My_Int) return My_Int is begin return M; end Ident; end Decls2; with Decls2; package Utils is procedure Put_Val (Arg : Decls2.My_Int); end Utils; with Text_IO; package body Utils is procedure Put_Val (Arg : Decls2.My_Int) is begin Text_IO.Put_Line (Decls2.My_Int'Image (Decls2.Ident (Arg))); end Put_Val; end Utils; with Decls1; procedure Main is begin Decls1.Lib_Task.Start; end; @end smallexample @noindent All we have done is to split @code{Decls} into two packages, one containing the library task, and one containing everything else. Now there is no cycle, and the program compiles, binds, links and executes using the default static model of elaboration. @item Declare separate task types. A significant part of the problem arises because of the use of the single task declaration form. This means that the elaboration of the task type, and the elaboration of the task itself (i.e.@: the creation of the task) happen at the same time. A good rule of style in Ada is to always create explicit task types. By following the additional step of placing task objects in separate packages from the task type declaration, many elaboration problems are avoided. Here is another modified example of the example program: @smallexample @c ada package Decls is task type Lib_Task_Type is entry Start; end Lib_Task_Type; type My_Int is new Integer; function Ident (M : My_Int) return My_Int; end Decls; with Utils; package body Decls is task body Lib_Task_Type is begin accept Start; Utils.Put_Val (2); end Lib_Task_Type; function Ident (M : My_Int) return My_Int is begin return M; end Ident; end Decls; with Decls; package Utils is procedure Put_Val (Arg : Decls.My_Int); end Utils; with Text_IO; package body Utils is procedure Put_Val (Arg : Decls.My_Int) is begin Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg))); end Put_Val; end Utils; with Decls; package Declst is Lib_Task : Decls.Lib_Task_Type; end Declst; with Declst; procedure Main is begin Declst.Lib_Task.Start; end; @end smallexample @noindent What we have done here is to replace the @code{task} declaration in package @code{Decls} with a @code{task type} declaration. Then we introduce a separate package @code{Declst} to contain the actual task object. This separates the elaboration issues for the @code{task type} declaration, which causes no trouble, from the elaboration issues of the task object, which is also unproblematic, since it is now independent of the elaboration of @code{Utils}. This separation of concerns also corresponds to a generally sound engineering principle of separating declarations from instances. This version of the program also compiles, binds, links, and executes, generating the expected output. @item Use No_Entry_Calls_In_Elaboration_Code restriction. @cindex No_Entry_Calls_In_Elaboration_Code The previous two approaches described how a program can be restructured to avoid the special problems caused by library task bodies. in practice, however, such restructuring may be difficult to apply to existing legacy code, so we must consider solutions that do not require massive rewriting. Let us consider more carefully why our original sample program works under the dynamic model of elaboration. The reason is that the code in the task body blocks immediately on the @code{accept} statement. Now of course there is nothing to prohibit elaboration code from making entry calls (for example from another library level task), so we cannot tell in isolation that the task will not execute the accept statement during elaboration. However, in practice it is very unusual to see elaboration code make any entry calls, and the pattern of tasks starting at elaboration time and then immediately blocking on @code{accept} or @code{select} statements is very common. What this means is that the compiler is being too pessimistic when it analyzes the whole package body as though it might be executed at elaboration time. If we know that the elaboration code contains no entry calls, (a very safe assumption most of the time, that could almost be made the default behavior), then we can compile all units of the program under control of the following configuration pragma: @smallexample pragma Restrictions (No_Entry_Calls_In_Elaboration_Code); @end smallexample @noindent This pragma can be placed in the @file{gnat.adc} file in the usual manner. If we take our original unmodified program and compile it in the presence of a @file{gnat.adc} containing the above pragma, then once again, we can compile, bind, link, and execute, obtaining the expected result. In the presence of this pragma, the compiler does not trace calls in a task body, that appear after the first @code{accept} or @code{select} statement, and therefore does not report a potential circularity in the original program. The compiler will check to the extent it can that the above restriction is not violated, but it is not always possible to do a complete check at compile time, so it is important to use this pragma only if the stated restriction is in fact met, that is to say no task receives an entry call before elaboration of all units is completed. @end itemize @node Mixing Elaboration Models @section Mixing Elaboration Models @noindent So far, we have assumed that the entire program is either compiled using the dynamic model or static model, ensuring consistency. It is possible to mix the two models, but rules have to be followed if this mixing is done to ensure that elaboration checks are not omitted. The basic rule is that @emph{a unit compiled with the static model cannot be @code{with'ed} by a unit compiled with the dynamic model}. The reason for this is that in the static model, a unit assumes that its clients guarantee to use (the equivalent of) pragma @code{Elaborate_All} so that no elaboration checks are required in inner subprograms, and this assumption is violated if the client is compiled with dynamic checks. The precise rule is as follows. A unit that is compiled with dynamic checks can only @code{with} a unit that meets at least one of the following criteria: @itemize @bullet @item The @code{with'ed} unit is itself compiled with dynamic elaboration checks (that is with the @option{-gnatE} switch. @item The @code{with'ed} unit is an internal GNAT implementation unit from the System, Interfaces, Ada, or GNAT hierarchies. @item The @code{with'ed} unit has pragma Preelaborate or pragma Pure. @item The @code{with'ing} unit (that is the client) has an explicit pragma @code{Elaborate_All} for the @code{with'ed} unit. @end itemize @noindent If this rule is violated, that is if a unit with dynamic elaboration checks @code{with's} a unit that does not meet one of the above four criteria, then the binder (@code{gnatbind}) will issue a warning similar to that in the following example: @smallexample warning: "x.ads" has dynamic elaboration checks and with's warning: "y.ads" which has static elaboration checks @end smallexample @noindent These warnings indicate that the rule has been violated, and that as a result elaboration checks may be missed in the resulting executable file. This warning may be suppressed using the @option{-ws} binder switch in the usual manner. One useful application of this mixing rule is in the case of a subsystem which does not itself @code{with} units from the remainder of the application. In this case, the entire subsystem can be compiled with dynamic checks to resolve a circularity in the subsystem, while allowing the main application that uses this subsystem to be compiled using the more reliable default static model. @node What to Do If the Default Elaboration Behavior Fails @section What to Do If the Default Elaboration Behavior Fails @noindent If the binder cannot find an acceptable order, it outputs detailed diagnostics. For example: @smallexample @group @iftex @leftskip=0cm @end iftex error: elaboration circularity detected info: "proc (body)" must be elaborated before "pack (body)" info: reason: Elaborate_All probably needed in unit "pack (body)" info: recompile "pack (body)" with -gnatwl info: for full details info: "proc (body)" info: is needed by its spec: info: "proc (spec)" info: which is withed by: info: "pack (body)" info: "pack (body)" must be elaborated before "proc (body)" info: reason: pragma Elaborate in unit "proc (body)" @end group @end smallexample @noindent In this case we have a cycle that the binder cannot break. On the one hand, there is an explicit pragma Elaborate in @code{proc} for @code{pack}. This means that the body of @code{pack} must be elaborated before the body of @code{proc}. On the other hand, there is elaboration code in @code{pack} that calls a subprogram in @code{proc}. This means that for maximum safety, there should really be a pragma Elaborate_All in @code{pack} for @code{proc} which would require that the body of @code{proc} be elaborated before the body of @code{pack}. Clearly both requirements cannot be satisfied. Faced with a circularity of this kind, you have three different options. @table @asis @item Fix the program The most desirable option from the point of view of long-term maintenance is to rearrange the program so that the elaboration problems are avoided. One useful technique is to place the elaboration code into separate child packages. Another is to move some of the initialization code to explicitly called subprograms, where the program controls the order of initialization explicitly. Although this is the most desirable option, it may be impractical and involve too much modification, especially in the case of complex legacy code. @item Perform dynamic checks If the compilations are done using the @option{-gnatE} (dynamic elaboration check) switch, then GNAT behaves in a quite different manner. Dynamic checks are generated for all calls that could possibly result in raising an exception. With this switch, the compiler does not generate implicit @code{Elaborate} or @code{Elaborate_All} pragmas. The behavior then is exactly as specified in the @cite{Ada Reference Manual}. The binder will generate an executable program that may or may not raise @code{Program_Error}, and then it is the programmer's job to ensure that it does not raise an exception. Note that it is important to compile all units with the switch, it cannot be used selectively. @item Suppress checks The drawback of dynamic checks is that they generate a significant overhead at run time, both in space and time. If you are absolutely sure that your program cannot raise any elaboration exceptions, and you still want to use the dynamic elaboration model, then you can use the configuration pragma @code{Suppress (Elaboration_Check)} to suppress all such checks. For example this pragma could be placed in the @file{gnat.adc} file. @item Suppress checks selectively When you know that certain calls or instantiations in elaboration code cannot possibly lead to an elaboration error, and the binder nevertheless complains about implicit @code{Elaborate} and @code{Elaborate_All} pragmas that lead to elaboration circularities, it is possible to remove those warnings locally and obtain a program that will bind. Clearly this can be unsafe, and it is the responsibility of the programmer to make sure that the resulting program has no elaboration anomalies. The pragma @code{Suppress (Elaboration_Check)} can be used with different granularity to suppress warnings and break elaboration circularities: @itemize @bullet @item Place the pragma that names the called subprogram in the declarative part that contains the call. @item Place the pragma in the declarative part, without naming an entity. This disables warnings on all calls in the corresponding declarative region. @item Place the pragma in the package spec that declares the called subprogram, and name the subprogram. This disables warnings on all elaboration calls to that subprogram. @item Place the pragma in the package spec that declares the called subprogram, without naming any entity. This disables warnings on all elaboration calls to all subprograms declared in this spec. @item Use Pragma Elaborate As previously described in section @xref{Treatment of Pragma Elaborate}, GNAT in static mode assumes that a @code{pragma} Elaborate indicates correctly that no elaboration checks are required on calls to the designated unit. There may be cases in which the caller knows that no transitive calls can occur, so that a @code{pragma Elaborate} will be sufficient in a case where @code{pragma Elaborate_All} would cause a circularity. @end itemize @noindent These five cases are listed in order of decreasing safety, and therefore require increasing programmer care in their application. Consider the following program: @smallexample @c adanocomment package Pack1 is function F1 return Integer; X1 : Integer; end Pack1; package Pack2 is function F2 return Integer; function Pure (x : integer) return integer; -- pragma Suppress (Elaboration_Check, On => Pure); -- (3) -- pragma Suppress (Elaboration_Check); -- (4) end Pack2; with Pack2; package body Pack1 is function F1 return Integer is begin return 100; end F1; Val : integer := Pack2.Pure (11); -- Elab. call (1) begin declare -- pragma Suppress(Elaboration_Check, Pack2.F2); -- (1) -- pragma Suppress(Elaboration_Check); -- (2) begin X1 := Pack2.F2 + 1; -- Elab. call (2) end; end Pack1; with Pack1; package body Pack2 is function F2 return Integer is begin return Pack1.F1; end F2; function Pure (x : integer) return integer is begin return x ** 3 - 3 * x; end; end Pack2; with Pack1, Ada.Text_IO; procedure Proc3 is begin Ada.Text_IO.Put_Line(Pack1.X1'Img); -- 101 end Proc3; @end smallexample In the absence of any pragmas, an attempt to bind this program produces the following diagnostics: @smallexample @group @iftex @leftskip=.5cm @end iftex error: elaboration circularity detected info: "pack1 (body)" must be elaborated before "pack1 (body)" info: reason: Elaborate_All probably needed in unit "pack1 (body)" info: recompile "pack1 (body)" with -gnatwl for full details info: "pack1 (body)" info: must be elaborated along with its spec: info: "pack1 (spec)" info: which is withed by: info: "pack2 (body)" info: which must be elaborated along with its spec: info: "pack2 (spec)" info: which is withed by: info: "pack1 (body)" @end group @end smallexample The sources of the circularity are the two calls to @code{Pack2.Pure} and @code{Pack2.F2} in the body of @code{Pack1}. We can see that the call to F2 is safe, even though F2 calls F1, because the call appears after the elaboration of the body of F1. Therefore the pragma (1) is safe, and will remove the warning on the call. It is also possible to use pragma (2) because there are no other potentially unsafe calls in the block. @noindent The call to @code{Pure} is safe because this function does not depend on the state of @code{Pack2}. Therefore any call to this function is safe, and it is correct to place pragma (3) in the corresponding package spec. @noindent Finally, we could place pragma (4) in the spec of @code{Pack2} to disable warnings on all calls to functions declared therein. Note that this is not necessarily safe, and requires more detailed examination of the subprogram bodies involved. In particular, a call to @code{F2} requires that @code{F1} be already elaborated. @end table @noindent It is hard to generalize on which of these four approaches should be taken. Obviously if it is possible to fix the program so that the default treatment works, this is preferable, but this may not always be practical. It is certainly simple enough to use @option{-gnatE} but the danger in this case is that, even if the GNAT binder finds a correct elaboration order, it may not always do so, and certainly a binder from another Ada compiler might not. A combination of testing and analysis (for which the warnings generated with the @option{-gnatwl} switch can be useful) must be used to ensure that the program is free of errors. One switch that is useful in this testing is the @option{^-p (pessimistic elaboration order)^/PESSIMISTIC_ELABORATION_ORDER^} switch for @code{gnatbind}. Normally the binder tries to find an order that has the best chance of avoiding elaboration problems. However, if this switch is used, the binder plays a devil's advocate role, and tries to choose the order that has the best chance of failing. If your program works even with this switch, then it has a better chance of being error free, but this is still not a guarantee. For an example of this approach in action, consider the C-tests (executable tests) from the ACVC suite. If these are compiled and run with the default treatment, then all but one of them succeed without generating any error diagnostics from the binder. However, there is one test that fails, and this is not surprising, because the whole point of this test is to ensure that the compiler can handle cases where it is impossible to determine a correct order statically, and it checks that an exception is indeed raised at run time. This one test must be compiled and run using the @option{-gnatE} switch, and then it passes. Alternatively, the entire suite can be run using this switch. It is never wrong to run with the dynamic elaboration switch if your code is correct, and we assume that the C-tests are indeed correct (it is less efficient, but efficiency is not a factor in running the ACVC tests.) @node Elaboration for Access-to-Subprogram Values @section Elaboration for Access-to-Subprogram Values @cindex Access-to-subprogram @noindent Access-to-subprogram types (introduced in Ada 95) complicate the handling of elaboration. The trouble is that it becomes impossible to tell at compile time which procedure is being called. This means that it is not possible for the binder to analyze the elaboration requirements in this case. If at the point at which the access value is created (i.e., the evaluation of @code{P'Access} for a subprogram @code{P}), the body of the subprogram is known to have been elaborated, then the access value is safe, and its use does not require a check. This may be achieved by appropriate arrangement of the order of declarations if the subprogram is in the current unit, or, if the subprogram is in another unit, by using pragma @code{Pure}, @code{Preelaborate}, or @code{Elaborate_Body} on the referenced unit. If the referenced body is not known to have been elaborated at the point the access value is created, then any use of the access value must do a dynamic check, and this dynamic check will fail and raise a @code{Program_Error} exception if the body has not been elaborated yet. GNAT will generate the necessary checks, and in addition, if the @option{-gnatwl} switch is set, will generate warnings that such checks are required. The use of dynamic dispatching for tagged types similarly generates a requirement for dynamic checks, and premature calls to any primitive operation of a tagged type before the body of the operation has been elaborated, will result in the raising of @code{Program_Error}. @node Summary of Procedures for Elaboration Control @section Summary of Procedures for Elaboration Control @cindex Elaboration control @noindent First, compile your program with the default options, using none of the special elaboration control switches. If the binder successfully binds your program, then you can be confident that, apart from issues raised by the use of access-to-subprogram types and dynamic dispatching, the program is free of elaboration errors. If it is important that the program be portable, then use the @option{-gnatwl} switch to generate warnings about missing @code{Elaborate} or @code{Elaborate_All} pragmas, and supply the missing pragmas. If the program fails to bind using the default static elaboration handling, then you can fix the program to eliminate the binder message, or recompile the entire program with the @option{-gnatE} switch to generate dynamic elaboration checks, and, if you are sure there really are no elaboration problems, use a global pragma @code{Suppress (Elaboration_Check)}. @node Other Elaboration Order Considerations @section Other Elaboration Order Considerations @noindent This section has been entirely concerned with the issue of finding a valid elaboration order, as defined by the Ada Reference Manual. In a case where several elaboration orders are valid, the task is to find one of the possible valid elaboration orders (and the static model in GNAT will ensure that this is achieved). The purpose of the elaboration rules in the Ada Reference Manual is to make sure that no entity is accessed before it has been elaborated. For a subprogram, this means that the spec and body must have been elaborated before the subprogram is called. For an object, this means that the object must have been elaborated before its value is read or written. A violation of either of these two requirements is an access before elaboration order, and this section has been all about avoiding such errors. In the case where more than one order of elaboration is possible, in the sense that access before elaboration errors are avoided, then any one of the orders is ``correct'' in the sense that it meets the requirements of the Ada Reference Manual, and no such error occurs. However, it may be the case for a given program, that there are constraints on the order of elaboration that come not from consideration of avoiding elaboration errors, but rather from extra-lingual logic requirements. Consider this example: @smallexample @c ada with Init_Constants; package Constants is X : Integer := 0; Y : Integer := 0; end Constants; package Init_Constants is procedure P; -- require a body end Init_Constants; with Constants; package body Init_Constants is procedure P is begin null; end; begin Constants.X := 3; Constants.Y := 4; end Init_Constants; with Constants; package Calc is Z : Integer := Constants.X + Constants.Y; end Calc; with Calc; with Text_IO; use Text_IO; procedure Main is begin Put_Line (Calc.Z'Img); end Main; @end smallexample @noindent In this example, there is more than one valid order of elaboration. For example both the following are correct orders: @smallexample Init_Constants spec Constants spec Calc spec Init_Constants body Main body and Init_Constants spec Init_Constants body Constants spec Calc spec Main body @end smallexample @noindent There is no language rule to prefer one or the other, both are correct from an order of elaboration point of view. But the programmatic effects of the two orders are very different. In the first, the elaboration routine of @code{Calc} initializes @code{Z} to zero, and then the main program runs with this value of zero. But in the second order, the elaboration routine of @code{Calc} runs after the body of Init_Constants has set @code{X} and @code{Y} and thus @code{Z} is set to 7 before @code{Main} runs. One could perhaps by applying pretty clever non-artificial intelligence to the situation guess that it is more likely that the second order of elaboration is the one desired, but there is no formal linguistic reason to prefer one over the other. In fact in this particular case, GNAT will prefer the second order, because of the rule that bodies are elaborated as soon as possible, but it's just luck that this is what was wanted (if indeed the second order was preferred). If the program cares about the order of elaboration routines in a case like this, it is important to specify the order required. In this particular case, that could have been achieved by adding to the spec of Calc: @smallexample @c ada pragma Elaborate_All (Constants); @end smallexample @noindent which requires that the body (if any) and spec of @code{Constants}, as well as the body and spec of any unit @code{with}'ed by @code{Constants} be elaborated before @code{Calc} is elaborated. Clearly no automatic method can always guess which alternative you require, and if you are working with legacy code that had constraints of this kind which were not properly specified by adding @code{Elaborate} or @code{Elaborate_All} pragmas, then indeed it is possible that two different compilers can choose different orders. However, GNAT does attempt to diagnose the common situation where there are uninitialized variables in the visible part of a package spec, and the corresponding package body has an elaboration block that directly or indirectly initialized one or more of these variables. This is the situation in which a pragma Elaborate_Body is usually desirable, and GNAT will generate a warning that suggests this addition if it detects this situation. The @code{gnatbind} @option{^-p^/PESSIMISTIC_ELABORATION^} switch may be useful in smoking out problems. This switch causes bodies to be elaborated as late as possible instead of as early as possible. In the example above, it would have forced the choice of the first elaboration order. If you get different results when using this switch, and particularly if one set of results is right, and one is wrong as far as you are concerned, it shows that you have some missing @code{Elaborate} pragmas. For the example above, we have the following output: @smallexample gnatmake -f -q main main 7 gnatmake -f -q main -bargs -p main 0 @end smallexample @noindent It is of course quite unlikely that both these results are correct, so it is up to you in a case like this to investigate the source of the difference, by looking at the two elaboration orders that are chosen, and figuring out which is correct, and then adding the necessary @code{Elaborate} or @code{Elaborate_All} pragmas to ensure the desired order. @c ******************************* @node Conditional Compilation @appendix Conditional Compilation @c ******************************* @cindex Conditional compilation @noindent It is often necessary to arrange for a single source program to serve multiple purposes, where it is compiled in different ways to achieve these different goals. Some examples of the need for this feature are @itemize @bullet @item Adapting a program to a different hardware environment @item Adapting a program to a different target architecture @item Turning debugging features on and off @item Arranging for a program to compile with different compilers @end itemize @noindent In C, or C++, the typical approach would be to use the preprocessor that is defined as part of the language. The Ada language does not contain such a feature. This is not an oversight, but rather a very deliberate design decision, based on the experience that overuse of the preprocessing features in C and C++ can result in programs that are extremely difficult to maintain. For example, if we have ten switches that can be on or off, this means that there are a thousand separate programs, any one of which might not even be syntactically correct, and even if syntactically correct, the resulting program might not work correctly. Testing all combinations can quickly become impossible. Nevertheless, the need to tailor programs certainly exists, and in this Appendix we will discuss how this can be achieved using Ada in general, and GNAT in particular. @menu * Use of Boolean Constants:: * Debugging - A Special Case:: * Conditionalizing Declarations:: * Use of Alternative Implementations:: * Preprocessing:: @end menu @node Use of Boolean Constants @section Use of Boolean Constants @noindent In the case where the difference is simply which code sequence is executed, the cleanest solution is to use Boolean constants to control which code is executed. @smallexample @c ada @group FP_Initialize_Required : constant Boolean := True; @dots{} if FP_Initialize_Required then @dots{} end if; @end group @end smallexample @noindent Not only will the code inside the @code{if} statement not be executed if the constant Boolean is @code{False}, but it will also be completely deleted from the program. However, the code is only deleted after the @code{if} statement has been checked for syntactic and semantic correctness. (In contrast, with preprocessors the code is deleted before the compiler ever gets to see it, so it is not checked until the switch is turned on.) @cindex Preprocessors (contrasted with conditional compilation) Typically the Boolean constants will be in a separate package, something like: @smallexample @c ada @group package Config is FP_Initialize_Required : constant Boolean := True; Reset_Available : constant Boolean := False; @dots{} end Config; @end group @end smallexample @noindent The @code{Config} package exists in multiple forms for the various targets, with an appropriate script selecting the version of @code{Config} needed. Then any other unit requiring conditional compilation can do a @code{with} of @code{Config} to make the constants visible. @node Debugging - A Special Case @section Debugging - A Special Case @noindent A common use of conditional code is to execute statements (for example dynamic checks, or output of intermediate results) under control of a debug switch, so that the debugging behavior can be turned on and off. This can be done using a Boolean constant to control whether the code is active: @smallexample @c ada @group if Debugging then Put_Line ("got to the first stage!"); end if; @end group @end smallexample @noindent or @smallexample @c ada @group if Debugging and then Temperature > 999.0 then raise Temperature_Crazy; end if; @end group @end smallexample @noindent Since this is a common case, there are special features to deal with this in a convenient manner. For the case of tests, Ada 2005 has added a pragma @code{Assert} that can be used for such tests. This pragma is modeled @cindex pragma @code{Assert} on the @code{Assert} pragma that has always been available in GNAT, so this feature may be used with GNAT even if you are not using Ada 2005 features. The use of pragma @code{Assert} is described in @ref{Pragma Assert,,, gnat_rm, GNAT Reference Manual}, but as an example, the last test could be written: @smallexample @c ada pragma Assert (Temperature <= 999.0, "Temperature Crazy"); @end smallexample @noindent or simply @smallexample @c ada pragma Assert (Temperature <= 999.0); @end smallexample @noindent In both cases, if assertions are active and the temperature is excessive, the exception @code{Assert_Failure} will be raised, with the given string in the first case or a string indicating the location of the pragma in the second case used as the exception message. You can turn assertions on and off by using the @code{Assertion_Policy} pragma. @cindex pragma @code{Assertion_Policy} This is an Ada 2005 pragma which is implemented in all modes by GNAT, but only in the latest versions of GNAT which include Ada 2005 capability. Alternatively, you can use the @option{-gnata} switch @cindex @option{-gnata} switch to enable assertions from the command line (this is recognized by all versions of GNAT). For the example above with the @code{Put_Line}, the GNAT-specific pragma @code{Debug} can be used: @cindex pragma @code{Debug} @smallexample @c ada pragma Debug (Put_Line ("got to the first stage!")); @end smallexample @noindent If debug pragmas are enabled, the argument, which must be of the form of a procedure call, is executed (in this case, @code{Put_Line} will be called). Only one call can be present, but of course a special debugging procedure containing any code you like can be included in the program and then called in a pragma @code{Debug} argument as needed. One advantage of pragma @code{Debug} over the @code{if Debugging then} construct is that pragma @code{Debug} can appear in declarative contexts, such as at the very beginning of a procedure, before local declarations have been elaborated. Debug pragmas are enabled using either the @option{-gnata} switch that also controls assertions, or with a separate Debug_Policy pragma. @cindex pragma @code{Debug_Policy} The latter pragma is new in the Ada 2005 versions of GNAT (but it can be used in Ada 95 and Ada 83 programs as well), and is analogous to pragma @code{Assertion_Policy} to control assertions. @code{Assertion_Policy} and @code{Debug_Policy} are configuration pragmas, and thus they can appear in @file{gnat.adc} if you are not using a project file, or in the file designated to contain configuration pragmas in a project file. They then apply to all subsequent compilations. In practice the use of the @option{-gnata} switch is often the most convenient method of controlling the status of these pragmas. Note that a pragma is not a statement, so in contexts where a statement sequence is required, you can't just write a pragma on its own. You have to add a @code{null} statement. @smallexample @c ada @group if @dots{} then @dots{} -- some statements else pragma Assert (Num_Cases < 10); null; end if; @end group @end smallexample @node Conditionalizing Declarations @section Conditionalizing Declarations @noindent In some cases, it may be necessary to conditionalize declarations to meet different requirements. For example we might want a bit string whose length is set to meet some hardware message requirement. In some cases, it may be possible to do this using declare blocks controlled by conditional constants: @smallexample @c ada @group if Small_Machine then declare X : Bit_String (1 .. 10); begin @dots{} end; else declare X : Large_Bit_String (1 .. 1000); begin @dots{} end; end if; @end group @end smallexample @noindent Note that in this approach, both declarations are analyzed by the compiler so this can only be used where both declarations are legal, even though one of them will not be used. Another approach is to define integer constants, e.g.@: @code{Bits_Per_Word}, or Boolean constants, e.g.@: @code{Little_Endian}, and then write declarations that are parameterized by these constants. For example @smallexample @c ada @group for Rec use Field1 at 0 range Boolean'Pos (Little_Endian) * 10 .. Bits_Per_Word; end record; @end group @end smallexample @noindent If @code{Bits_Per_Word} is set to 32, this generates either @smallexample @c ada @group for Rec use Field1 at 0 range 0 .. 32; end record; @end group @end smallexample @noindent for the big endian case, or @smallexample @c ada @group for Rec use record Field1 at 0 range 10 .. 32; end record; @end group @end smallexample @noindent for the little endian case. Since a powerful subset of Ada expression notation is usable for creating static constants, clever use of this feature can often solve quite difficult problems in conditionalizing compilation (note incidentally that in Ada 95, the little endian constant was introduced as @code{System.Default_Bit_Order}, so you do not need to define this one yourself). @node Use of Alternative Implementations @section Use of Alternative Implementations @noindent In some cases, none of the approaches described above are adequate. This can occur for example if the set of declarations required is radically different for two different configurations. In this situation, the official Ada way of dealing with conditionalizing such code is to write separate units for the different cases. As long as this does not result in excessive duplication of code, this can be done without creating maintenance problems. The approach is to share common code as far as possible, and then isolate the code and declarations that are different. Subunits are often a convenient method for breaking out a piece of a unit that is to be conditionalized, with separate files for different versions of the subunit for different targets, where the build script selects the right one to give to the compiler. @cindex Subunits (and conditional compilation) As an example, consider a situation where a new feature in Ada 2005 allows something to be done in a really nice way. But your code must be able to compile with an Ada 95 compiler. Conceptually you want to say: @smallexample @c ada @group if Ada_2005 then @dots{} neat Ada 2005 code else @dots{} not quite as neat Ada 95 code end if; @end group @end smallexample @noindent where @code{Ada_2005} is a Boolean constant. But this won't work when @code{Ada_2005} is set to @code{False}, since the @code{then} clause will be illegal for an Ada 95 compiler. (Recall that although such unreachable code would eventually be deleted by the compiler, it still needs to be legal. If it uses features introduced in Ada 2005, it will be illegal in Ada 95.) So instead we write @smallexample @c ada procedure Insert is separate; @end smallexample @noindent Then we have two files for the subunit @code{Insert}, with the two sets of code. If the package containing this is called @code{File_Queries}, then we might have two files @itemize @bullet @item @file{file_queries-insert-2005.adb} @item @file{file_queries-insert-95.adb} @end itemize @noindent and the build script renames the appropriate file to @smallexample file_queries-insert.adb @end smallexample @noindent and then carries out the compilation. This can also be done with project files' naming schemes. For example: @smallexample @c project For Body ("File_Queries.Insert") use "file_queries-insert-2005.ada"; @end smallexample @noindent Note also that with project files it is desirable to use a different extension than @file{ads} / @file{adb} for alternative versions. Otherwise a naming conflict may arise through another commonly used feature: to declare as part of the project a set of directories containing all the sources obeying the default naming scheme. The use of alternative units is certainly feasible in all situations, and for example the Ada part of the GNAT run-time is conditionalized based on the target architecture using this approach. As a specific example, consider the implementation of the AST feature in VMS. There is one spec: @smallexample s-asthan.ads @end smallexample @noindent which is the same for all architectures, and three bodies: @table @file @item s-asthan.adb used for all non-VMS operating systems @item s-asthan-vms-alpha.adb used for VMS on the Alpha @item s-asthan-vms-ia64.adb used for VMS on the ia64 @end table @noindent The dummy version @file{s-asthan.adb} simply raises exceptions noting that this operating system feature is not available, and the two remaining versions interface with the corresponding versions of VMS to provide VMS-compatible AST handling. The GNAT build script knows the architecture and operating system, and automatically selects the right version, renaming it if necessary to @file{s-asthan.adb} before the run-time build. Another style for arranging alternative implementations is through Ada's access-to-subprogram facility. In case some functionality is to be conditionally included, you can declare an access-to-procedure variable @code{Ref} that is initialized to designate a ``do nothing'' procedure, and then invoke @code{Ref.all} when appropriate. In some library package, set @code{Ref} to @code{Proc'Access} for some procedure @code{Proc} that performs the relevant processing. The initialization only occurs if the library package is included in the program. The same idea can also be implemented using tagged types and dispatching calls. @node Preprocessing @section Preprocessing @cindex Preprocessing @noindent Although it is quite possible to conditionalize code without the use of C-style preprocessing, as described earlier in this section, it is nevertheless convenient in some cases to use the C approach. Moreover, older Ada compilers have often provided some preprocessing capability, so legacy code may depend on this approach, even though it is not standard. To accommodate such use, GNAT provides a preprocessor (modeled to a large extent on the various preprocessors that have been used with legacy code on other compilers, to enable easier transition). The preprocessor may be used in two separate modes. It can be used quite separately from the compiler, to generate a separate output source file that is then fed to the compiler as a separate step. This is the @code{gnatprep} utility, whose use is fully described in @ref{Preprocessing Using gnatprep}. @cindex @code{gnatprep} The preprocessing language allows such constructs as @smallexample @group #if DEBUG or PRIORITY > 4 then bunch of declarations #else completely different bunch of declarations #end if; @end group @end smallexample @noindent The values of the symbols @code{DEBUG} and @code{PRIORITY} can be defined either on the command line or in a separate file. The other way of running the preprocessor is even closer to the C style and often more convenient. In this approach the preprocessing is integrated into the compilation process. The compiler is fed the preprocessor input which includes @code{#if} lines etc, and then the compiler carries out the preprocessing internally and processes the resulting output. For more details on this approach, see @ref{Integrated Preprocessing}. @c ******************************* @node Inline Assembler @appendix Inline Assembler @c ******************************* @noindent If you need to write low-level software that interacts directly with the hardware, Ada provides two ways to incorporate assembly language code into your program. First, you can import and invoke external routines written in assembly language, an Ada feature fully supported by GNAT@. However, for small sections of code it may be simpler or more efficient to include assembly language statements directly in your Ada source program, using the facilities of the implementation-defined package @code{System.Machine_Code}, which incorporates the gcc Inline Assembler. The Inline Assembler approach offers a number of advantages, including the following: @itemize @bullet @item No need to use non-Ada tools @item Consistent interface over different targets @item Automatic usage of the proper calling conventions @item Access to Ada constants and variables @item Definition of intrinsic routines @item Possibility of inlining a subprogram comprising assembler code @item Code optimizer can take Inline Assembler code into account @end itemize This chapter presents a series of examples to show you how to use the Inline Assembler. Although it focuses on the Intel x86, the general approach applies also to other processors. It is assumed that you are familiar with Ada and with assembly language programming. @menu * Basic Assembler Syntax:: * A Simple Example of Inline Assembler:: * Output Variables in Inline Assembler:: * Input Variables in Inline Assembler:: * Inlining Inline Assembler Code:: * Other Asm Functionality:: @end menu @c --------------------------------------------------------------------------- @node Basic Assembler Syntax @section Basic Assembler Syntax @noindent The assembler used by GNAT and gcc is based not on the Intel assembly language, but rather on a language that descends from the AT&T Unix assembler @emph{as} (and which is often referred to as ``AT&T syntax''). The following table summarizes the main features of @emph{as} syntax and points out the differences from the Intel conventions. See the gcc @emph{as} and @emph{gas} (an @emph{as} macro pre-processor) documentation for further information. @table @asis @item Register names gcc / @emph{as}: Prefix with ``%''; for example @code{%eax} @* Intel: No extra punctuation; for example @code{eax} @item Immediate operand gcc / @emph{as}: Prefix with ``$''; for example @code{$4} @* Intel: No extra punctuation; for example @code{4} @item Address gcc / @emph{as}: Prefix with ``$''; for example @code{$loc} @* Intel: No extra punctuation; for example @code{loc} @item Memory contents gcc / @emph{as}: No extra punctuation; for example @code{loc} @* Intel: Square brackets; for example @code{[loc]} @item Register contents gcc / @emph{as}: Parentheses; for example @code{(%eax)} @* Intel: Square brackets; for example @code{[eax]} @item Hexadecimal numbers gcc / @emph{as}: Leading ``0x'' (C language syntax); for example @code{0xA0} @* Intel: Trailing ``h''; for example @code{A0h} @item Operand size gcc / @emph{as}: Explicit in op code; for example @code{movw} to move a 16-bit word @* Intel: Implicit, deduced by assembler; for example @code{mov} @item Instruction repetition gcc / @emph{as}: Split into two lines; for example @* @code{rep} @* @code{stosl} @* Intel: Keep on one line; for example @code{rep stosl} @item Order of operands gcc / @emph{as}: Source first; for example @code{movw $4, %eax} @* Intel: Destination first; for example @code{mov eax, 4} @end table @c --------------------------------------------------------------------------- @node A Simple Example of Inline Assembler @section A Simple Example of Inline Assembler @noindent The following example will generate a single assembly language statement, @code{nop}, which does nothing. Despite its lack of run-time effect, the example will be useful in illustrating the basics of the Inline Assembler facility. @smallexample @c ada @group with System.Machine_Code; use System.Machine_Code; procedure Nothing is begin Asm ("nop"); end Nothing; @end group @end smallexample @code{Asm} is a procedure declared in package @code{System.Machine_Code}; here it takes one parameter, a @emph{template string} that must be a static expression and that will form the generated instruction. @code{Asm} may be regarded as a compile-time procedure that parses the template string and additional parameters (none here), from which it generates a sequence of assembly language instructions. The examples in this chapter will illustrate several of the forms for invoking @code{Asm}; a complete specification of the syntax is found in @ref{Machine Code Insertions,,, gnat_rm, GNAT Reference Manual}. Under the standard GNAT conventions, the @code{Nothing} procedure should be in a file named @file{nothing.adb}. You can build the executable in the usual way: @smallexample gnatmake nothing @end smallexample However, the interesting aspect of this example is not its run-time behavior but rather the generated assembly code. To see this output, invoke the compiler as follows: @smallexample gcc -c -S -fomit-frame-pointer -gnatp @file{nothing.adb} @end smallexample where the options are: @table @code @item -c compile only (no bind or link) @item -S generate assembler listing @item -fomit-frame-pointer do not set up separate stack frames @item -gnatp do not add runtime checks @end table This gives a human-readable assembler version of the code. The resulting file will have the same name as the Ada source file, but with a @code{.s} extension. In our example, the file @file{nothing.s} has the following contents: @smallexample @group .file "nothing.adb" gcc2_compiled.: ___gnu_compiled_ada: .text .align 4 .globl __ada_nothing __ada_nothing: #APP nop #NO_APP jmp L1 .align 2,0x90 L1: ret @end group @end smallexample The assembly code you included is clearly indicated by the compiler, between the @code{#APP} and @code{#NO_APP} delimiters. The character before the 'APP' and 'NOAPP' can differ on different targets. For example, GNU/Linux uses '#APP' while on NT you will see '/APP'. If you make a mistake in your assembler code (such as using the wrong size modifier, or using a wrong operand for the instruction) GNAT will report this error in a temporary file, which will be deleted when the compilation is finished. Generating an assembler file will help in such cases, since you can assemble this file separately using the @emph{as} assembler that comes with gcc. Assembling the file using the command @smallexample as @file{nothing.s} @end smallexample @noindent will give you error messages whose lines correspond to the assembler input file, so you can easily find and correct any mistakes you made. If there are no errors, @emph{as} will generate an object file @file{nothing.out}. @c --------------------------------------------------------------------------- @node Output Variables in Inline Assembler @section Output Variables in Inline Assembler @noindent The examples in this section, showing how to access the processor flags, illustrate how to specify the destination operands for assembly language statements. @smallexample @c ada @group with Interfaces; use Interfaces; with Ada.Text_IO; use Ada.Text_IO; with System.Machine_Code; use System.Machine_Code; procedure Get_Flags is Flags : Unsigned_32; use ASCII; begin Asm ("pushfl" & LF & HT & -- push flags on stack "popl %%eax" & LF & HT & -- load eax with flags "movl %%eax, %0", -- store flags in variable Outputs => Unsigned_32'Asm_Output ("=g", Flags)); Put_Line ("Flags register:" & Flags'Img); end Get_Flags; @end group @end smallexample In order to have a nicely aligned assembly listing, we have separated multiple assembler statements in the Asm template string with linefeed (ASCII.LF) and horizontal tab (ASCII.HT) characters. The resulting section of the assembly output file is: @smallexample @group #APP pushfl popl %eax movl %eax, -40(%ebp) #NO_APP @end group @end smallexample It would have been legal to write the Asm invocation as: @smallexample Asm ("pushfl popl %%eax movl %%eax, %0") @end smallexample but in the generated assembler file, this would come out as: @smallexample #APP pushfl popl %eax movl %eax, -40(%ebp) #NO_APP @end smallexample which is not so convenient for the human reader. We use Ada comments at the end of each line to explain what the assembler instructions actually do. This is a useful convention. When writing Inline Assembler instructions, you need to precede each register and variable name with a percent sign. Since the assembler already requires a percent sign at the beginning of a register name, you need two consecutive percent signs for such names in the Asm template string, thus @code{%%eax}. In the generated assembly code, one of the percent signs will be stripped off. Names such as @code{%0}, @code{%1}, @code{%2}, etc., denote input or output variables: operands you later define using @code{Input} or @code{Output} parameters to @code{Asm}. An output variable is illustrated in the third statement in the Asm template string: @smallexample movl %%eax, %0 @end smallexample The intent is to store the contents of the eax register in a variable that can be accessed in Ada. Simply writing @code{movl %%eax, Flags} would not necessarily work, since the compiler might optimize by using a register to hold Flags, and the expansion of the @code{movl} instruction would not be aware of this optimization. The solution is not to store the result directly but rather to advise the compiler to choose the correct operand form; that is the purpose of the @code{%0} output variable. Information about the output variable is supplied in the @code{Outputs} parameter to @code{Asm}: @smallexample Outputs => Unsigned_32'Asm_Output ("=g", Flags)); @end smallexample The output is defined by the @code{Asm_Output} attribute of the target type; the general format is @smallexample Type'Asm_Output (constraint_string, variable_name) @end smallexample The constraint string directs the compiler how to store/access the associated variable. In the example @smallexample Unsigned_32'Asm_Output ("=m", Flags); @end smallexample the @code{"m"} (memory) constraint tells the compiler that the variable @code{Flags} should be stored in a memory variable, thus preventing the optimizer from keeping it in a register. In contrast, @smallexample Unsigned_32'Asm_Output ("=r", Flags); @end smallexample uses the @code{"r"} (register) constraint, telling the compiler to store the variable in a register. If the constraint is preceded by the equal character (@strong{=}), it tells the compiler that the variable will be used to store data into it. In the @code{Get_Flags} example, we used the @code{"g"} (global) constraint, allowing the optimizer to choose whatever it deems best. There are a fairly large number of constraints, but the ones that are most useful (for the Intel x86 processor) are the following: @table @code @item = output constraint @item g global (i.e.@: can be stored anywhere) @item m in memory @item I a constant @item a use eax @item b use ebx @item c use ecx @item d use edx @item S use esi @item D use edi @item r use one of eax, ebx, ecx or edx @item q use one of eax, ebx, ecx, edx, esi or edi @end table The full set of constraints is described in the gcc and @emph{as} documentation; note that it is possible to combine certain constraints in one constraint string. You specify the association of an output variable with an assembler operand through the @code{%}@emph{n} notation, where @emph{n} is a non-negative integer. Thus in @smallexample @c ada @group Asm ("pushfl" & LF & HT & -- push flags on stack "popl %%eax" & LF & HT & -- load eax with flags "movl %%eax, %0", -- store flags in variable Outputs => Unsigned_32'Asm_Output ("=g", Flags)); @end group @end smallexample @noindent @code{%0} will be replaced in the expanded code by the appropriate operand, whatever the compiler decided for the @code{Flags} variable. In general, you may have any number of output variables: @itemize @bullet @item Count the operands starting at 0; thus @code{%0}, @code{%1}, etc. @item Specify the @code{Outputs} parameter as a parenthesized comma-separated list of @code{Asm_Output} attributes @end itemize For example: @smallexample @c ada @group Asm ("movl %%eax, %0" & LF & HT & "movl %%ebx, %1" & LF & HT & "movl %%ecx, %2", Outputs => (Unsigned_32'Asm_Output ("=g", Var_A), -- %0 = Var_A Unsigned_32'Asm_Output ("=g", Var_B), -- %1 = Var_B Unsigned_32'Asm_Output ("=g", Var_C))); -- %2 = Var_C @end group @end smallexample @noindent where @code{Var_A}, @code{Var_B}, and @code{Var_C} are variables in the Ada program. As a variation on the @code{Get_Flags} example, we can use the constraints string to direct the compiler to store the eax register into the @code{Flags} variable, instead of including the store instruction explicitly in the @code{Asm} template string: @smallexample @c ada @group with Interfaces; use Interfaces; with Ada.Text_IO; use Ada.Text_IO; with System.Machine_Code; use System.Machine_Code; procedure Get_Flags_2 is Flags : Unsigned_32; use ASCII; begin Asm ("pushfl" & LF & HT & -- push flags on stack "popl %%eax", -- save flags in eax Outputs => Unsigned_32'Asm_Output ("=a", Flags)); Put_Line ("Flags register:" & Flags'Img); end Get_Flags_2; @end group @end smallexample @noindent The @code{"a"} constraint tells the compiler that the @code{Flags} variable will come from the eax register. Here is the resulting code: @smallexample @group #APP pushfl popl %eax #NO_APP movl %eax,-40(%ebp) @end group @end smallexample @noindent The compiler generated the store of eax into Flags after expanding the assembler code. Actually, there was no need to pop the flags into the eax register; more simply, we could just pop the flags directly into the program variable: @smallexample @c ada @group with Interfaces; use Interfaces; with Ada.Text_IO; use Ada.Text_IO; with System.Machine_Code; use System.Machine_Code; procedure Get_Flags_3 is Flags : Unsigned_32; use ASCII; begin Asm ("pushfl" & LF & HT & -- push flags on stack "pop %0", -- save flags in Flags Outputs => Unsigned_32'Asm_Output ("=g", Flags)); Put_Line ("Flags register:" & Flags'Img); end Get_Flags_3; @end group @end smallexample @c --------------------------------------------------------------------------- @node Input Variables in Inline Assembler @section Input Variables in Inline Assembler @noindent The example in this section illustrates how to specify the source operands for assembly language statements. The program simply increments its input value by 1: @smallexample @c ada @group with Interfaces; use Interfaces; with Ada.Text_IO; use Ada.Text_IO; with System.Machine_Code; use System.Machine_Code; procedure Increment is function Incr (Value : Unsigned_32) return Unsigned_32 is Result : Unsigned_32; begin Asm ("incl %0", Inputs => Unsigned_32'Asm_Input ("a", Value), Outputs => Unsigned_32'Asm_Output ("=a", Result)); return Result; end Incr; Value : Unsigned_32; begin Value := 5; Put_Line ("Value before is" & Value'Img); Value := Incr (Value); Put_Line ("Value after is" & Value'Img); end Increment; @end group @end smallexample The @code{Outputs} parameter to @code{Asm} specifies that the result will be in the eax register and that it is to be stored in the @code{Result} variable. The @code{Inputs} parameter looks much like the @code{Outputs} parameter, but with an @code{Asm_Input} attribute. The @code{"="} constraint, indicating an output value, is not present. You can have multiple input variables, in the same way that you can have more than one output variable. The parameter count (%0, %1) etc, now starts at the first input statement, and continues with the output statements. When both parameters use the same variable, the compiler will treat them as the same %n operand, which is the case here. Just as the @code{Outputs} parameter causes the register to be stored into the target variable after execution of the assembler statements, so does the @code{Inputs} parameter cause its variable to be loaded into the register before execution of the assembler statements. Thus the effect of the @code{Asm} invocation is: @enumerate @item load the 32-bit value of @code{Value} into eax @item execute the @code{incl %eax} instruction @item store the contents of eax into the @code{Result} variable @end enumerate The resulting assembler file (with @option{-O2} optimization) contains: @smallexample @group _increment__incr.1: subl $4,%esp movl 8(%esp),%eax #APP incl %eax #NO_APP movl %eax,%edx movl %ecx,(%esp) addl $4,%esp ret @end group @end smallexample @c --------------------------------------------------------------------------- @node Inlining Inline Assembler Code @section Inlining Inline Assembler Code @noindent For a short subprogram such as the @code{Incr} function in the previous section, the overhead of the call and return (creating / deleting the stack frame) can be significant, compared to the amount of code in the subprogram body. A solution is to apply Ada's @code{Inline} pragma to the subprogram, which directs the compiler to expand invocations of the subprogram at the point(s) of call, instead of setting up a stack frame for out-of-line calls. Here is the resulting program: @smallexample @c ada @group with Interfaces; use Interfaces; with Ada.Text_IO; use Ada.Text_IO; with System.Machine_Code; use System.Machine_Code; procedure Increment_2 is function Incr (Value : Unsigned_32) return Unsigned_32 is Result : Unsigned_32; begin Asm ("incl %0", Inputs => Unsigned_32'Asm_Input ("a", Value), Outputs => Unsigned_32'Asm_Output ("=a", Result)); return Result; end Incr; pragma Inline (Increment); Value : Unsigned_32; begin Value := 5; Put_Line ("Value before is" & Value'Img); Value := Increment (Value); Put_Line ("Value after is" & Value'Img); end Increment_2; @end group @end smallexample Compile the program with both optimization (@option{-O2}) and inlining (@option{-gnatn}) enabled. The @code{Incr} function is still compiled as usual, but at the point in @code{Increment} where our function used to be called: @smallexample @group pushl %edi call _increment__incr.1 @end group @end smallexample @noindent the code for the function body directly appears: @smallexample @group movl %esi,%eax #APP incl %eax #NO_APP movl %eax,%edx @end group @end smallexample @noindent thus saving the overhead of stack frame setup and an out-of-line call. @c --------------------------------------------------------------------------- @node Other Asm Functionality @section Other @code{Asm} Functionality @noindent This section describes two important parameters to the @code{Asm} procedure: @code{Clobber}, which identifies register usage; and @code{Volatile}, which inhibits unwanted optimizations. @menu * The Clobber Parameter:: * The Volatile Parameter:: @end menu @c --------------------------------------------------------------------------- @node The Clobber Parameter @subsection The @code{Clobber} Parameter @noindent One of the dangers of intermixing assembly language and a compiled language such as Ada is that the compiler needs to be aware of which registers are being used by the assembly code. In some cases, such as the earlier examples, the constraint string is sufficient to indicate register usage (e.g., @code{"a"} for the eax register). But more generally, the compiler needs an explicit identification of the registers that are used by the Inline Assembly statements. Using a register that the compiler doesn't know about could be a side effect of an instruction (like @code{mull} storing its result in both eax and edx). It can also arise from explicit register usage in your assembly code; for example: @smallexample @group Asm ("movl %0, %%ebx" & LF & HT & "movl %%ebx, %1", Inputs => Unsigned_32'Asm_Input ("g", Var_In), Outputs => Unsigned_32'Asm_Output ("=g", Var_Out)); @end group @end smallexample @noindent where the compiler (since it does not analyze the @code{Asm} template string) does not know you are using the ebx register. In such cases you need to supply the @code{Clobber} parameter to @code{Asm}, to identify the registers that will be used by your assembly code: @smallexample @group Asm ("movl %0, %%ebx" & LF & HT & "movl %%ebx, %1", Inputs => Unsigned_32'Asm_Input ("g", Var_In), Outputs => Unsigned_32'Asm_Output ("=g", Var_Out), Clobber => "ebx"); @end group @end smallexample The Clobber parameter is a static string expression specifying the register(s) you are using. Note that register names are @emph{not} prefixed by a percent sign. Also, if more than one register is used then their names are separated by commas; e.g., @code{"eax, ebx"} The @code{Clobber} parameter has several additional uses: @enumerate @item Use ``register'' name @code{cc} to indicate that flags might have changed @item Use ``register'' name @code{memory} if you changed a memory location @end enumerate @c --------------------------------------------------------------------------- @node The Volatile Parameter @subsection The @code{Volatile} Parameter @cindex Volatile parameter @noindent Compiler optimizations in the presence of Inline Assembler may sometimes have unwanted effects. For example, when an @code{Asm} invocation with an input variable is inside a loop, the compiler might move the loading of the input variable outside the loop, regarding it as a one-time initialization. If this effect is not desired, you can disable such optimizations by setting the @code{Volatile} parameter to @code{True}; for example: @smallexample @c ada @group Asm ("movl %0, %%ebx" & LF & HT & "movl %%ebx, %1", Inputs => Unsigned_32'Asm_Input ("g", Var_In), Outputs => Unsigned_32'Asm_Output ("=g", Var_Out), Clobber => "ebx", Volatile => True); @end group @end smallexample By default, @code{Volatile} is set to @code{False} unless there is no @code{Outputs} parameter. Although setting @code{Volatile} to @code{True} prevents unwanted optimizations, it will also disable other optimizations that might be important for efficiency. In general, you should set @code{Volatile} to @code{True} only if the compiler's optimizations have created problems. @c END OF INLINE ASSEMBLER CHAPTER @c =============================== @c *********************************** @c * Compatibility and Porting Guide * @c *********************************** @node Compatibility and Porting Guide @appendix Compatibility and Porting Guide @noindent This chapter describes the compatibility issues that may arise between GNAT and other Ada compilation systems (including those for Ada 83), and shows how GNAT can expedite porting applications developed in other Ada environments. @menu * Compatibility with Ada 83:: * Compatibility between Ada 95 and Ada 2005:: * Implementation-dependent characteristics:: * Compatibility with Other Ada Systems:: * Representation Clauses:: @ifclear vms @c Brief section is only in non-VMS version @c Full chapter is in VMS version * Compatibility with HP Ada 83:: @end ifclear @ifset vms * Transitioning to 64-Bit GNAT for OpenVMS:: @end ifset @end menu @node Compatibility with Ada 83 @section Compatibility with Ada 83 @cindex Compatibility (between Ada 83 and Ada 95 / Ada 2005) @noindent Ada 95 and Ada 2005 are highly upwards compatible with Ada 83. In particular, the design intention was that the difficulties associated with moving from Ada 83 to Ada 95 or Ada 2005 should be no greater than those that occur when moving from one Ada 83 system to another. However, there are a number of points at which there are minor incompatibilities. The @cite{Ada 95 Annotated Reference Manual} contains full details of these issues, and should be consulted for a complete treatment. In practice the following subsections treat the most likely issues to be encountered. @menu * Legal Ada 83 programs that are illegal in Ada 95:: * More deterministic semantics:: * Changed semantics:: * Other language compatibility issues:: @end menu @node Legal Ada 83 programs that are illegal in Ada 95 @subsection Legal Ada 83 programs that are illegal in Ada 95 Some legal Ada 83 programs are illegal (i.e., they will fail to compile) in Ada 95 and thus also in Ada 2005: @table @emph @item Character literals Some uses of character literals are ambiguous. Since Ada 95 has introduced @code{Wide_Character} as a new predefined character type, some uses of character literals that were legal in Ada 83 are illegal in Ada 95. For example: @smallexample @c ada for Char in 'A' .. 'Z' loop @dots{} end loop; @end smallexample @noindent The problem is that @code{'A'} and @code{'Z'} could be from either @code{Character} or @code{Wide_Character}. The simplest correction is to make the type explicit; e.g.: @smallexample @c ada for Char in Character range 'A' .. 'Z' loop @dots{} end loop; @end smallexample @item New reserved words The identifiers @code{abstract}, @code{aliased}, @code{protected}, @code{requeue}, @code{tagged}, and @code{until} are reserved in Ada 95. Existing Ada 83 code using any of these identifiers must be edited to use some alternative name. @item Freezing rules The rules in Ada 95 are slightly different with regard to the point at which entities are frozen, and representation pragmas and clauses are not permitted past the freeze point. This shows up most typically in the form of an error message complaining that a representation item appears too late, and the appropriate corrective action is to move the item nearer to the declaration of the entity to which it refers. A particular case is that representation pragmas @ifset vms (including the extended HP Ada 83 compatibility pragmas such as @code{Export_Procedure}) @end ifset cannot be applied to a subprogram body. If necessary, a separate subprogram declaration must be introduced to which the pragma can be applied. @item Optional bodies for library packages In Ada 83, a package that did not require a package body was nevertheless allowed to have one. This lead to certain surprises in compiling large systems (situations in which the body could be unexpectedly ignored by the binder). In Ada 95, if a package does not require a body then it is not permitted to have a body. To fix this problem, simply remove a redundant body if it is empty, or, if it is non-empty, introduce a dummy declaration into the spec that makes the body required. One approach is to add a private part to the package declaration (if necessary), and define a parameterless procedure called @code{Requires_Body}, which must then be given a dummy procedure body in the package body, which then becomes required. Another approach (assuming that this does not introduce elaboration circularities) is to add an @code{Elaborate_Body} pragma to the package spec, since one effect of this pragma is to require the presence of a package body. @item @code{Numeric_Error} is now the same as @code{Constraint_Error} In Ada 95, the exception @code{Numeric_Error} is a renaming of @code{Constraint_Error}. This means that it is illegal to have separate exception handlers for the two exceptions. The fix is simply to remove the handler for the @code{Numeric_Error} case (since even in Ada 83, a compiler was free to raise @code{Constraint_Error} in place of @code{Numeric_Error} in all cases). @item Indefinite subtypes in generics In Ada 83, it was permissible to pass an indefinite type (e.g.@: @code{String}) as the actual for a generic formal private type, but then the instantiation would be illegal if there were any instances of declarations of variables of this type in the generic body. In Ada 95, to avoid this clear violation of the methodological principle known as the ``contract model'', the generic declaration explicitly indicates whether or not such instantiations are permitted. If a generic formal parameter has explicit unknown discriminants, indicated by using @code{(<>)} after the type name, then it can be instantiated with indefinite types, but no stand-alone variables can be declared of this type. Any attempt to declare such a variable will result in an illegality at the time the generic is declared. If the @code{(<>)} notation is not used, then it is illegal to instantiate the generic with an indefinite type. This is the potential incompatibility issue when porting Ada 83 code to Ada 95. It will show up as a compile time error, and the fix is usually simply to add the @code{(<>)} to the generic declaration. @end table @node More deterministic semantics @subsection More deterministic semantics @table @emph @item Conversions Conversions from real types to integer types round away from 0. In Ada 83 the conversion Integer(2.5) could deliver either 2 or 3 as its value. This implementation freedom was intended to support unbiased rounding in statistical applications, but in practice it interfered with portability. In Ada 95 the conversion semantics are unambiguous, and rounding away from 0 is required. Numeric code may be affected by this change in semantics. Note, though, that this issue is no worse than already existed in Ada 83 when porting code from one vendor to another. @item Tasking The Real-Time Annex introduces a set of policies that define the behavior of features that were implementation dependent in Ada 83, such as the order in which open select branches are executed. @end table @node Changed semantics @subsection Changed semantics @noindent The worst kind of incompatibility is one where a program that is legal in Ada 83 is also legal in Ada 95 but can have an effect in Ada 95 that was not possible in Ada 83. Fortunately this is extremely rare, but the one situation that you should be alert to is the change in the predefined type @code{Character} from 7-bit ASCII to 8-bit Latin-1. @table @emph @item Range of type @code{Character} The range of @code{Standard.Character} is now the full 256 characters of Latin-1, whereas in most Ada 83 implementations it was restricted to 128 characters. Although some of the effects of this change will be manifest in compile-time rejection of legal Ada 83 programs it is possible for a working Ada 83 program to have a different effect in Ada 95, one that was not permitted in Ada 83. As an example, the expression @code{Character'Pos(Character'Last)} returned @code{127} in Ada 83 and now delivers @code{255} as its value. In general, you should look at the logic of any character-processing Ada 83 program and see whether it needs to be adapted to work correctly with Latin-1. Note that the predefined Ada 95 API has a character handling package that may be relevant if code needs to be adapted to account for the additional Latin-1 elements. The desirable fix is to modify the program to accommodate the full character set, but in some cases it may be convenient to define a subtype or derived type of Character that covers only the restricted range. @cindex Latin-1 @end table @node Other language compatibility issues @subsection Other language compatibility issues @table @emph @item @option{-gnat83} switch All implementations of GNAT provide a switch that causes GNAT to operate in Ada 83 mode. In this mode, some but not all compatibility problems of the type described above are handled automatically. For example, the new reserved words introduced in Ada 95 and Ada 2005 are treated simply as identifiers as in Ada 83. However, in practice, it is usually advisable to make the necessary modifications to the program to remove the need for using this switch. See @ref{Compiling Different Versions of Ada}. @item Support for removed Ada 83 pragmas and attributes A number of pragmas and attributes from Ada 83 were removed from Ada 95, generally because they were replaced by other mechanisms. Ada 95 and Ada 2005 compilers are allowed, but not required, to implement these missing elements. In contrast with some other compilers, GNAT implements all such pragmas and attributes, eliminating this compatibility concern. These include @code{pragma Interface} and the floating point type attributes (@code{Emax}, @code{Mantissa}, etc.), among other items. @end table @node Compatibility between Ada 95 and Ada 2005 @section Compatibility between Ada 95 and Ada 2005 @cindex Compatibility between Ada 95 and Ada 2005 @noindent Although Ada 2005 was designed to be upwards compatible with Ada 95, there are a number of incompatibilities. Several are enumerated below; for a complete description please see the Annotated Ada 2005 Reference Manual, or section 9.1.1 in @cite{Rationale for Ada 2005}. @table @emph @item New reserved words. The words @code{interface}, @code{overriding} and @code{synchronized} are reserved in Ada 2005. A pre-Ada 2005 program that uses any of these as an identifier will be illegal. @item New declarations in predefined packages. A number of packages in the predefined environment contain new declarations: @code{Ada.Exceptions}, @code{Ada.Real_Time}, @code{Ada.Strings}, @code{Ada.Strings.Fixed}, @code{Ada.Strings.Bounded}, @code{Ada.Strings.Unbounded}, @code{Ada.Strings.Wide_Fixed}, @code{Ada.Strings.Wide_Bounded}, @code{Ada.Strings.Wide_Unbounded}, @code{Ada.Tags}, @code{Ada.Text_IO}, and @code{Interfaces.C}. If an Ada 95 program does a @code{with} and @code{use} of any of these packages, the new declarations may cause name clashes. @item Access parameters. A nondispatching subprogram with an access parameter cannot be renamed as a dispatching operation. This was permitted in Ada 95. @item Access types, discriminants, and constraints. Rule changes in this area have led to some incompatibilities; for example, constrained subtypes of some access types are not permitted in Ada 2005. @item Aggregates for limited types. The allowance of aggregates for limited types in Ada 2005 raises the possibility of ambiguities in legal Ada 95 programs, since additional types now need to be considered in expression resolution. @item Fixed-point multiplication and division. Certain expressions involving ``*'' or ``/'' for a fixed-point type, which were legal in Ada 95 and invoked the predefined versions of these operations, are now ambiguous. The ambiguity may be resolved either by applying a type conversion to the expression, or by explicitly invoking the operation from package @code{Standard}. @item Return-by-reference types. The Ada 95 return-by-reference mechanism has been removed. Instead, the user can declare a function returning a value from an anonymous access type. @end table @node Implementation-dependent characteristics @section Implementation-dependent characteristics @noindent Although the Ada language defines the semantics of each construct as precisely as practical, in some situations (for example for reasons of efficiency, or where the effect is heavily dependent on the host or target platform) the implementation is allowed some freedom. In porting Ada 83 code to GNAT, you need to be aware of whether / how the existing code exercised such implementation dependencies. Such characteristics fall into several categories, and GNAT offers specific support in assisting the transition from certain Ada 83 compilers. @menu * Implementation-defined pragmas:: * Implementation-defined attributes:: * Libraries:: * Elaboration order:: * Target-specific aspects:: @end menu @node Implementation-defined pragmas @subsection Implementation-defined pragmas @noindent Ada compilers are allowed to supplement the language-defined pragmas, and these are a potential source of non-portability. All GNAT-defined pragmas are described in @ref{Implementation Defined Pragmas,,, gnat_rm, GNAT Reference Manual}, and these include several that are specifically intended to correspond to other vendors' Ada 83 pragmas. For migrating from VADS, the pragma @code{Use_VADS_Size} may be useful. For compatibility with HP Ada 83, GNAT supplies the pragmas @code{Extend_System}, @code{Ident}, @code{Inline_Generic}, @code{Interface_Name}, @code{Passive}, @code{Suppress_All}, and @code{Volatile}. Other relevant pragmas include @code{External} and @code{Link_With}. Some vendor-specific Ada 83 pragmas (@code{Share_Generic}, @code{Subtitle}, and @code{Title}) are recognized, thus avoiding compiler rejection of units that contain such pragmas; they are not relevant in a GNAT context and hence are not otherwise implemented. @node Implementation-defined attributes @subsection Implementation-defined attributes Analogous to pragmas, the set of attributes may be extended by an implementation. All GNAT-defined attributes are described in @ref{Implementation Defined Attributes,,, gnat_rm, GNAT Reference Manual}, and these include several that are specifically intended to correspond to other vendors' Ada 83 attributes. For migrating from VADS, the attribute @code{VADS_Size} may be useful. For compatibility with HP Ada 83, GNAT supplies the attributes @code{Bit}, @code{Machine_Size} and @code{Type_Class}. @node Libraries @subsection Libraries @noindent Vendors may supply libraries to supplement the standard Ada API. If Ada 83 code uses vendor-specific libraries then there are several ways to manage this in Ada 95 or Ada 2005: @enumerate @item If the source code for the libraries (specs and bodies) are available, then the libraries can be migrated in the same way as the application. @item If the source code for the specs but not the bodies are available, then you can reimplement the bodies. @item Some features introduced by Ada 95 obviate the need for library support. For example most Ada 83 vendors supplied a package for unsigned integers. The Ada 95 modular type feature is the preferred way to handle this need, so instead of migrating or reimplementing the unsigned integer package it may be preferable to retrofit the application using modular types. @end enumerate @node Elaboration order @subsection Elaboration order @noindent The implementation can choose any elaboration order consistent with the unit dependency relationship. This freedom means that some orders can result in Program_Error being raised due to an ``Access Before Elaboration'': an attempt to invoke a subprogram its body has been elaborated, or to instantiate a generic before the generic body has been elaborated. By default GNAT attempts to choose a safe order (one that will not encounter access before elaboration problems) by implicitly inserting @code{Elaborate} or @code{Elaborate_All} pragmas where needed. However, this can lead to the creation of elaboration circularities and a resulting rejection of the program by gnatbind. This issue is thoroughly described in @ref{Elaboration Order Handling in GNAT}. In brief, there are several ways to deal with this situation: @itemize @bullet @item Modify the program to eliminate the circularities, e.g.@: by moving elaboration-time code into explicitly-invoked procedures @item Constrain the elaboration order by including explicit @code{Elaborate_Body} or @code{Elaborate} pragmas, and then inhibit the generation of implicit @code{Elaborate_All} pragmas either globally (as an effect of the @option{-gnatE} switch) or locally (by selectively suppressing elaboration checks via pragma @code{Suppress(Elaboration_Check)} when it is safe to do so). @end itemize @node Target-specific aspects @subsection Target-specific aspects @noindent Low-level applications need to deal with machine addresses, data representations, interfacing with assembler code, and similar issues. If such an Ada 83 application is being ported to different target hardware (for example where the byte endianness has changed) then you will need to carefully examine the program logic; the porting effort will heavily depend on the robustness of the original design. Moreover, Ada 95 (and thus Ada 2005) are sometimes incompatible with typical Ada 83 compiler practices regarding implicit packing, the meaning of the Size attribute, and the size of access values. GNAT's approach to these issues is described in @ref{Representation Clauses}. @node Compatibility with Other Ada Systems @section Compatibility with Other Ada Systems @noindent If programs avoid the use of implementation dependent and implementation defined features, as documented in the @cite{Ada Reference Manual}, there should be a high degree of portability between GNAT and other Ada systems. The following are specific items which have proved troublesome in moving Ada 95 programs from GNAT to other Ada 95 compilers, but do not affect porting code to GNAT@. (As of @value{NOW}, GNAT is the only compiler available for Ada 2005; the following issues may or may not arise for Ada 2005 programs when other compilers appear.) @table @emph @item Ada 83 Pragmas and Attributes Ada 95 compilers are allowed, but not required, to implement the missing Ada 83 pragmas and attributes that are no longer defined in Ada 95. GNAT implements all such pragmas and attributes, eliminating this as a compatibility concern, but some other Ada 95 compilers reject these pragmas and attributes. @item Specialized Needs Annexes GNAT implements the full set of special needs annexes. At the current time, it is the only Ada 95 compiler to do so. This means that programs making use of these features may not be portable to other Ada 95 compilation systems. @item Representation Clauses Some other Ada 95 compilers implement only the minimal set of representation clauses required by the Ada 95 reference manual. GNAT goes far beyond this minimal set, as described in the next section. @end table @node Representation Clauses @section Representation Clauses @noindent The Ada 83 reference manual was quite vague in describing both the minimal required implementation of representation clauses, and also their precise effects. Ada 95 (and thus also Ada 2005) are much more explicit, but the minimal set of capabilities required is still quite limited. GNAT implements the full required set of capabilities in Ada 95 and Ada 2005, but also goes much further, and in particular an effort has been made to be compatible with existing Ada 83 usage to the greatest extent possible. A few cases exist in which Ada 83 compiler behavior is incompatible with the requirements in Ada 95 (and thus also Ada 2005). These are instances of intentional or accidental dependence on specific implementation dependent characteristics of these Ada 83 compilers. The following is a list of the cases most likely to arise in existing Ada 83 code. @table @emph @item Implicit Packing Some Ada 83 compilers allowed a Size specification to cause implicit packing of an array or record. This could cause expensive implicit conversions for change of representation in the presence of derived types, and the Ada design intends to avoid this possibility. Subsequent AI's were issued to make it clear that such implicit change of representation in response to a Size clause is inadvisable, and this recommendation is represented explicitly in the Ada 95 (and Ada 2005) Reference Manuals as implementation advice that is followed by GNAT@. The problem will show up as an error message rejecting the size clause. The fix is simply to provide the explicit pragma @code{Pack}, or for more fine tuned control, provide a Component_Size clause. @item Meaning of Size Attribute The Size attribute in Ada 95 (and Ada 2005) for discrete types is defined as the minimal number of bits required to hold values of the type. For example, on a 32-bit machine, the size of @code{Natural} will typically be 31 and not 32 (since no sign bit is required). Some Ada 83 compilers gave 31, and some 32 in this situation. This problem will usually show up as a compile time error, but not always. It is a good idea to check all uses of the 'Size attribute when porting Ada 83 code. The GNAT specific attribute Object_Size can provide a useful way of duplicating the behavior of some Ada 83 compiler systems. @item Size of Access Types A common assumption in Ada 83 code is that an access type is in fact a pointer, and that therefore it will be the same size as a System.Address value. This assumption is true for GNAT in most cases with one exception. For the case of a pointer to an unconstrained array type (where the bounds may vary from one value of the access type to another), the default is to use a ``fat pointer'', which is represented as two separate pointers, one to the bounds, and one to the array. This representation has a number of advantages, including improved efficiency. However, it may cause some difficulties in porting existing Ada 83 code which makes the assumption that, for example, pointers fit in 32 bits on a machine with 32-bit addressing. To get around this problem, GNAT also permits the use of ``thin pointers'' for access types in this case (where the designated type is an unconstrained array type). These thin pointers are indeed the same size as a System.Address value. To specify a thin pointer, use a size clause for the type, for example: @smallexample @c ada type X is access all String; for X'Size use Standard'Address_Size; @end smallexample @noindent which will cause the type X to be represented using a single pointer. When using this representation, the bounds are right behind the array. This representation is slightly less efficient, and does not allow quite such flexibility in the use of foreign pointers or in using the Unrestricted_Access attribute to create pointers to non-aliased objects. But for any standard portable use of the access type it will work in a functionally correct manner and allow porting of existing code. Note that another way of forcing a thin pointer representation is to use a component size clause for the element size in an array, or a record representation clause for an access field in a record. @end table @ifclear vms @c This brief section is only in the non-VMS version @c The complete chapter on HP Ada is in the VMS version @node Compatibility with HP Ada 83 @section Compatibility with HP Ada 83 @noindent The VMS version of GNAT fully implements all the pragmas and attributes provided by HP Ada 83, as well as providing the standard HP Ada 83 libraries, including Starlet. In addition, data layouts and parameter passing conventions are highly compatible. This means that porting existing HP Ada 83 code to GNAT in VMS systems should be easier than most other porting efforts. The following are some of the most significant differences between GNAT and HP Ada 83. @table @emph @item Default floating-point representation In GNAT, the default floating-point format is IEEE, whereas in HP Ada 83, it is VMS format. GNAT does implement the necessary pragmas (Long_Float, Float_Representation) for changing this default. @item System The package System in GNAT exactly corresponds to the definition in the Ada 95 reference manual, which means that it excludes many of the HP Ada 83 extensions. However, a separate package Aux_DEC is provided that contains the additional definitions, and a special pragma, Extend_System allows this package to be treated transparently as an extension of package System. @item To_Address The definitions provided by Aux_DEC are exactly compatible with those in the HP Ada 83 version of System, with one exception. HP Ada provides the following declarations: @smallexample @c ada TO_ADDRESS (INTEGER) TO_ADDRESS (UNSIGNED_LONGWORD) TO_ADDRESS (@i{universal_integer}) @end smallexample @noindent The version of TO_ADDRESS taking a @i{universal integer} argument is in fact an extension to Ada 83 not strictly compatible with the reference manual. In GNAT, we are constrained to be exactly compatible with the standard, and this means we cannot provide this capability. In HP Ada 83, the point of this definition is to deal with a call like: @smallexample @c ada TO_ADDRESS (16#12777#); @end smallexample @noindent Normally, according to the Ada 83 standard, one would expect this to be ambiguous, since it matches both the INTEGER and UNSIGNED_LONGWORD forms of TO_ADDRESS@. However, in HP Ada 83, there is no ambiguity, since the definition using @i{universal_integer} takes precedence. In GNAT, since the version with @i{universal_integer} cannot be supplied, it is not possible to be 100% compatible. Since there are many programs using numeric constants for the argument to TO_ADDRESS, the decision in GNAT was to change the name of the function in the UNSIGNED_LONGWORD case, so the declarations provided in the GNAT version of AUX_Dec are: @smallexample @c ada function To_Address (X : Integer) return Address; pragma Pure_Function (To_Address); function To_Address_Long (X : Unsigned_Longword) return Address; pragma Pure_Function (To_Address_Long); @end smallexample @noindent This means that programs using TO_ADDRESS for UNSIGNED_LONGWORD must change the name to TO_ADDRESS_LONG@. @item Task_Id values The Task_Id values assigned will be different in the two systems, and GNAT does not provide a specified value for the Task_Id of the environment task, which in GNAT is treated like any other declared task. @end table @noindent For full details on these and other less significant compatibility issues, see appendix E of the HP publication entitled @cite{HP Ada, Technical Overview and Comparison on HP Platforms}. For GNAT running on other than VMS systems, all the HP Ada 83 pragmas and attributes are recognized, although only a subset of them can sensibly be implemented. The description of pragmas in @ref{Implementation Defined Pragmas,,, gnat_rm, GNAT Reference Manual} indicates whether or not they are applicable to non-VMS systems. @end ifclear @ifset vms @node Transitioning to 64-Bit GNAT for OpenVMS @section Transitioning to 64-Bit @value{EDITION} for OpenVMS @noindent This section is meant to assist users of pre-2006 @value{EDITION} for Alpha OpenVMS who are transitioning to 64-bit @value{EDITION}, the version of the GNAT technology supplied in 2006 and later for OpenVMS on both Alpha and I64. @menu * Introduction to transitioning:: * Migration of 32 bit code:: * Taking advantage of 64 bit addressing:: * Technical details:: @end menu @node Introduction to transitioning @subsection Introduction @noindent 64-bit @value{EDITION} for Open VMS has been designed to meet three main goals: @enumerate @item Providing a full conforming implementation of Ada 95 and Ada 2005 @item Allowing maximum backward compatibility, thus easing migration of existing Ada source code @item Supplying a path for exploiting the full 64-bit address range @end enumerate @noindent Ada's strong typing semantics has made it impractical to have different 32-bit and 64-bit modes. As soon as one object could possibly be outside the 32-bit address space, this would make it necessary for the @code{System.Address} type to be 64 bits. In particular, this would cause inconsistencies if 32-bit code is called from 64-bit code that raises an exception. This issue has been resolved by always using 64-bit addressing at the system level, but allowing for automatic conversions between 32-bit and 64-bit addresses where required. Thus users who do not currently require 64-bit addressing capabilities, can recompile their code with only minimal changes (and indeed if the code is written in portable Ada, with no assumptions about the size of the @code{Address} type, then no changes at all are necessary). At the same time, this approach provides a simple, gradual upgrade path to future use of larger memories than available for 32-bit systems. Also, newly written applications or libraries will by default be fully compatible with future systems exploiting 64-bit addressing capabilities. @ref{Migration of 32 bit code}, will focus on porting applications that do not require more than 2 GB of addressable memory. This code will be referred to as @emph{32-bit code}. For applications intending to exploit the full 64-bit address space, @ref{Taking advantage of 64 bit addressing}, will consider further changes that may be required. Such code will be referred to below as @emph{64-bit code}. @node Migration of 32 bit code @subsection Migration of 32-bit code @menu * Address types:: * Access types and 32/64-bit allocation:: * Unchecked conversions:: * Predefined constants:: * Interfacing with C:: * 32/64-bit descriptors:: * Experience with source compatibility:: @end menu @node Address types @subsubsection Address types @noindent To solve the problem of mixing 64-bit and 32-bit addressing, while maintaining maximum backward compatibility, the following approach has been taken: @itemize @bullet @item @code{System.Address} always has a size of 64 bits @cindex @code{System.Address} size @cindex @code{Address} size @item @code{System.Short_Address} is a 32-bit subtype of @code{System.Address} @cindex @code{System.Short_Address} size @cindex @code{Short_Address} size @end itemize @noindent Since @code{System.Short_Address} is a subtype of @code{System.Address}, a @code{Short_Address} may be used where an @code{Address} is required, and vice versa, without needing explicit type conversions. By virtue of the Open VMS parameter passing conventions, even imported and exported subprograms that have 32-bit address parameters are compatible with those that have 64-bit address parameters. (See @ref{Making code 64 bit clean} for details.) The areas that may need attention are those where record types have been defined that contain components of the type @code{System.Address}, and where objects of this type are passed to code expecting a record layout with 32-bit addresses. Different compilers on different platforms cannot be expected to represent the same type in the same way, since alignment constraints and other system-dependent properties affect the compiler's decision. For that reason, Ada code generally uses representation clauses to specify the expected layout where required. If such a representation clause uses 32 bits for a component having the type @code{System.Address}, 64-bit @value{EDITION} for OpenVMS will detect that error and produce a specific diagnostic message. The developer should then determine whether the representation should be 64 bits or not and make either of two changes: change the size to 64 bits and leave the type as @code{System.Address}, or leave the size as 32 bits and change the type to @code{System.Short_Address}. Since @code{Short_Address} is a subtype of @code{Address}, no changes are required in any code setting or accessing the field; the compiler will automatically perform any needed conversions between address formats. @node Access types and 32/64-bit allocation @subsubsection Access types and 32/64-bit allocation @cindex 32-bit allocation @cindex 64-bit allocation @noindent By default, objects designated by access values are always allocated in the 64-bit address space, and access values themselves are represented in 64 bits. If these defaults are not appropriate, and 32-bit allocation is required (for example if the address of an allocated object is assigned to a @code{Short_Address} variable), then several alternatives are available: @itemize @bullet @item A pool-specific access type (ie, an @w{Ada 83} access type, whose definition is @code{access T} versus @code{access all T} or @code{access constant T}), may be declared with a @code{'Size} representation clause that establishes the size as 32 bits. In such circumstances allocations for that type will be from the 32-bit heap. Such a clause is not permitted for a general access type (declared with @code{access all} or @code{access constant}) as values of such types must be able to refer to any object of the designated type, including objects residing outside the 32-bit address range. Existing @w{Ada 83} code will not contain such type definitions, however, since general access types were introduced in @w{Ada 95}. @item Switches for @command{GNAT BIND} control whether the internal GNAT allocation routine @code{__gnat_malloc} uses 64-bit or 32-bit allocations. @cindex @code{__gnat_malloc} The switches are respectively @option{-H64} (the default) and @option{-H32}. @cindex @option{-H32} (@command{gnatbind}) @cindex @option{-H64} (@command{gnatbind}) @item The environment variable (logical name) @code{GNAT$NO_MALLOC_64} @cindex @code{GNAT$NO_MALLOC_64} environment variable may be used to force @code{__gnat_malloc} to use 32-bit allocation. If this variable is left undefined, or defined as @code{"DISABLE"}, @code{"FALSE"}, or @code{"0"}, then the default (64-bit) allocation is used. If defined as @code{"ENABLE"}, @code{"TRUE"}, or @code{"1"}, then 32-bit allocation is used. The gnatbind qualifiers described above override this logical name. @item A ^gcc switch^gcc switch^ for OpenVMS, @option{-mno-malloc64}, operates @cindex @option{-mno-malloc64} (^gcc^gcc^) at a low level to convert explicit calls to @code{malloc} and related functions from the C run-time library so that they perform allocations in the 32-bit heap. Since all internal allocations from GNAT use @code{__gnat_malloc}, this switch is not required unless the program makes explicit calls on @code{malloc} (or related functions) from interfaced C code. @end itemize @node Unchecked conversions @subsubsection Unchecked conversions @noindent In the case of an @code{Unchecked_Conversion} where the source type is a 64-bit access type or the type @code{System.Address}, and the target type is a 32-bit type, the compiler will generate a warning. Even though the generated code will still perform the required conversions, it is highly recommended in these cases to use respectively a 32-bit access type or @code{System.Short_Address} as the source type. @node Predefined constants @subsubsection Predefined constants @noindent The following table shows the correspondence between pre-2006 versions of @value{EDITION} on Alpha OpenVMS (``Old'') and 64-bit @value{EDITION} (``New''): @multitable {@code{System.Short_Memory_Size}} {2**32} {2**64} @item @b{Constant} @tab @b{Old} @tab @b{New} @item @code{System.Word_Size} @tab 32 @tab 64 @item @code{System.Memory_Size} @tab 2**32 @tab 2**64 @item @code{System.Short_Memory_Size} @tab 2**32 @tab 2**32 @item @code{System.Address_Size} @tab 32 @tab 64 @end multitable @noindent If you need to refer to the specific memory size of a 32-bit implementation, instead of the actual memory size, use @code{System.Short_Memory_Size} rather than @code{System.Memory_Size}. Similarly, references to @code{System.Address_Size} may need to be replaced by @code{System.Short_Address'Size}. The program @command{gnatfind} may be useful for locating references to the above constants, so that you can verify that they are still correct. @node Interfacing with C @subsubsection Interfacing with C @noindent In order to minimize the impact of the transition to 64-bit addresses on legacy programs, some fundamental types in the @code{Interfaces.C} package hierarchy continue to be represented in 32 bits. These types are: @code{ptrdiff_t}, @code{size_t}, and @code{chars_ptr}. This eases integration with the default HP C layout choices, for example as found in the system routines in @code{DECC$SHR.EXE}. Because of this implementation choice, the type fully compatible with @code{chars_ptr} is now @code{Short_Address} and not @code{Address}. Depending on the context the compiler will issue a warning or an error when type @code{Address} is used, alerting the user to a potential problem. Otherwise 32-bit programs that use @code{Interfaces.C} should normally not require code modifications The other issue arising with C interfacing concerns pragma @code{Convention}. For VMS 64-bit systems, there is an issue of the appropriate default size of C convention pointers in the absence of an explicit size clause. The HP C compiler can choose either 32 or 64 bits depending on compiler options. GNAT chooses 32-bits rather than 64-bits in the default case where no size clause is given. This proves a better choice for porting 32-bit legacy applications. In order to have a 64-bit representation, it is necessary to specify a size representation clause. For example: @smallexample @c ada type int_star is access Interfaces.C.int; pragma Convention(C, int_star); for int_star'Size use 64; -- Necessary to get 64 and not 32 bits @end smallexample @node 32/64-bit descriptors @subsubsection 32/64-bit descriptors @noindent By default, GNAT uses a 64-bit descriptor mechanism. For an imported subprogram (i.e., a subprogram identified by pragma @code{Import_Function}, @code{Import_Procedure}, or @code{Import_Valued_Procedure}) that specifies @code{Short_Descriptor} as its mechanism, a 32-bit descriptor is used. @cindex @code{Short_Descriptor} mechanism for imported subprograms If the configuration pragma @code{Short_Descriptors} is supplied, then all descriptors will be 32 bits. @cindex pragma @code{Short_Descriptors} @node Experience with source compatibility @subsubsection Experience with source compatibility @noindent The Security Server and STARLET on I64 provide an interesting ``test case'' for source compatibility issues, since it is in such system code where assumptions about @code{Address} size might be expected to occur. Indeed, there were a small number of occasions in the Security Server file @file{jibdef.ads} where a representation clause for a record type specified 32 bits for a component of type @code{Address}. All of these errors were detected by the compiler. The repair was obvious and immediate; to simply replace @code{Address} by @code{Short_Address}. In the case of STARLET, there were several record types that should have had representation clauses but did not. In these record types there was an implicit assumption that an @code{Address} value occupied 32 bits. These compiled without error, but their usage resulted in run-time error returns from STARLET system calls. Future GNAT technology enhancements may include a tool that detects and flags these sorts of potential source code porting problems. @c **************************************** @node Taking advantage of 64 bit addressing @subsection Taking advantage of 64-bit addressing @menu * Making code 64 bit clean:: * Allocating memory from the 64 bit storage pool:: * Restrictions on use of 64 bit objects:: * STARLET and other predefined libraries:: @end menu @node Making code 64 bit clean @subsubsection Making code 64-bit clean @noindent In order to prevent problems that may occur when (parts of) a system start using memory outside the 32-bit address range, we recommend some additional guidelines: @itemize @bullet @item For imported subprograms that take parameters of the type @code{System.Address}, ensure that these subprograms can indeed handle 64-bit addresses. If not, or when in doubt, change the subprogram declaration to specify @code{System.Short_Address} instead. @item Resolve all warnings related to size mismatches in unchecked conversions. Failing to do so causes erroneous execution if the source object is outside the 32-bit address space. @item (optional) Explicitly use the 32-bit storage pool for access types used in a 32-bit context, or use generic access types where possible (@pxref{Restrictions on use of 64 bit objects}). @end itemize @noindent If these rules are followed, the compiler will automatically insert any necessary checks to ensure that no addresses or access values passed to 32-bit code ever refer to objects outside the 32-bit address range. Any attempt to do this will raise @code{Constraint_Error}. @node Allocating memory from the 64 bit storage pool @subsubsection Allocating memory from the 64-bit storage pool @noindent By default, all allocations -- for both pool-specific and general access types -- use the 64-bit storage pool. To override this default, for an individual access type or globally, see @ref{Access types and 32/64-bit allocation}. @node Restrictions on use of 64 bit objects @subsubsection Restrictions on use of 64-bit objects @noindent Taking the address of an object allocated from a 64-bit storage pool, and then passing this address to a subprogram expecting @code{System.Short_Address}, or assigning it to a variable of type @code{Short_Address}, will cause @code{Constraint_Error} to be raised. In case the code is not 64-bit clean (@pxref{Making code 64 bit clean}), or checks are suppressed, no exception is raised and execution will become erroneous. @node STARLET and other predefined libraries @subsubsection STARLET and other predefined libraries @noindent All code that comes as part of GNAT is 64-bit clean, but the restrictions given in @ref{Restrictions on use of 64 bit objects}, still apply. Look at the package specs to see in which contexts objects allocated in 64-bit address space are acceptable. @node Technical details @subsection Technical details @noindent 64-bit @value{EDITION} for Open VMS takes advantage of the freedom given in the Ada standard with respect to the type of @code{System.Address}. Previous versions of GNAT Pro have defined this type as private and implemented it as a modular type. In order to allow defining @code{System.Short_Address} as a proper subtype, and to match the implicit sign extension in parameter passing, in 64-bit @value{EDITION} for Open VMS, @code{System.Address} is defined as a visible (i.e., non-private) integer type. Standard operations on the type, such as the binary operators ``+'', ``-'', etc., that take @code{Address} operands and return an @code{Address} result, have been hidden by declaring these @code{abstract}, a feature introduced in Ada 95 that helps avoid the potential ambiguities that would otherwise result from overloading. (Note that, although @code{Address} is a visible integer type, good programming practice dictates against exploiting the type's integer properties such as literals, since this will compromise code portability.) Defining @code{Address} as a visible integer type helps achieve maximum compatibility for existing Ada code, without sacrificing the capabilities of the 64-bit architecture. @end ifset @c ************************************************ @ifset unw @node Microsoft Windows Topics @appendix Microsoft Windows Topics @cindex Windows NT @cindex Windows 95 @cindex Windows 98 @noindent This chapter describes topics that are specific to the Microsoft Windows platforms (NT, 2000, and XP Professional). @menu * Using GNAT on Windows:: * Using a network installation of GNAT:: * CONSOLE and WINDOWS subsystems:: * Temporary Files:: * Mixed-Language Programming on Windows:: * Windows Calling Conventions:: * Introduction to Dynamic Link Libraries (DLLs):: * Using DLLs with GNAT:: * Building DLLs with GNAT Project files:: * Building DLLs with GNAT:: * Building DLLs with gnatdll:: * GNAT and Windows Resources:: * Debugging a DLL:: * Setting Stack Size from gnatlink:: * Setting Heap Size from gnatlink:: @end menu @node Using GNAT on Windows @section Using GNAT on Windows @noindent One of the strengths of the GNAT technology is that its tool set (@command{gcc}, @command{gnatbind}, @command{gnatlink}, @command{gnatmake}, the @code{gdb} debugger, etc.) is used in the same way regardless of the platform. On Windows this tool set is complemented by a number of Microsoft-specific tools that have been provided to facilitate interoperability with Windows when this is required. With these tools: @itemize @bullet @item You can build applications using the @code{CONSOLE} or @code{WINDOWS} subsystems. @item You can use any Dynamically Linked Library (DLL) in your Ada code (both relocatable and non-relocatable DLLs are supported). @item You can build Ada DLLs for use in other applications. These applications can be written in a language other than Ada (e.g., C, C++, etc). Again both relocatable and non-relocatable Ada DLLs are supported. @item You can include Windows resources in your Ada application. @item You can use or create COM/DCOM objects. @end itemize @noindent Immediately below are listed all known general GNAT-for-Windows restrictions. Other restrictions about specific features like Windows Resources and DLLs are listed in separate sections below. @itemize @bullet @item It is not possible to use @code{GetLastError} and @code{SetLastError} when tasking, protected records, or exceptions are used. In these cases, in order to implement Ada semantics, the GNAT run-time system calls certain Win32 routines that set the last error variable to 0 upon success. It should be possible to use @code{GetLastError} and @code{SetLastError} when tasking, protected record, and exception features are not used, but it is not guaranteed to work. @item It is not possible to link against Microsoft libraries except for import libraries. Interfacing must be done by the mean of DLLs. @item When the compilation environment is located on FAT32 drives, users may experience recompilations of the source files that have not changed if Daylight Saving Time (DST) state has changed since the last time files were compiled. NTFS drives do not have this problem. @item No components of the GNAT toolset use any entries in the Windows registry. The only entries that can be created are file associations and PATH settings, provided the user has chosen to create them at installation time, as well as some minimal book-keeping information needed to correctly uninstall or integrate different GNAT products. @end itemize @node Using a network installation of GNAT @section Using a network installation of GNAT @noindent Make sure the system on which GNAT is installed is accessible from the current machine, i.e., the install location is shared over the network. Shared resources are accessed on Windows by means of UNC paths, which have the format @code{\\server\sharename\path} In order to use such a network installation, simply add the UNC path of the @file{bin} directory of your GNAT installation in front of your PATH. For example, if GNAT is installed in @file{\GNAT} directory of a share location called @file{c-drive} on a machine @file{LOKI}, the following command will make it available: @code{@ @ @ path \\loki\c-drive\gnat\bin;%path%} Be aware that every compilation using the network installation results in the transfer of large amounts of data across the network and will likely cause serious performance penalty. @node CONSOLE and WINDOWS subsystems @section CONSOLE and WINDOWS subsystems @cindex CONSOLE Subsystem @cindex WINDOWS Subsystem @cindex -mwindows @noindent There are two main subsystems under Windows. The @code{CONSOLE} subsystem (which is the default subsystem) will always create a console when launching the application. This is not something desirable when the application has a Windows GUI. To get rid of this console the application must be using the @code{WINDOWS} subsystem. To do so the @option{-mwindows} linker option must be specified. @smallexample $ gnatmake winprog -largs -mwindows @end smallexample @node Temporary Files @section Temporary Files @cindex Temporary files @noindent It is possible to control where temporary files gets created by setting the @env{TMP} environment variable. The file will be created: @itemize @item Under the directory pointed to by the @env{TMP} environment variable if this directory exists. @item Under @file{c:\temp}, if the @env{TMP} environment variable is not set (or not pointing to a directory) and if this directory exists. @item Under the current working directory otherwise. @end itemize @noindent This allows you to determine exactly where the temporary file will be created. This is particularly useful in networked environments where you may not have write access to some directories. @node Mixed-Language Programming on Windows @section Mixed-Language Programming on Windows @noindent Developing pure Ada applications on Windows is no different than on other GNAT-supported platforms. However, when developing or porting an application that contains a mix of Ada and C/C++, the choice of your Windows C/C++ development environment conditions your overall interoperability strategy. If you use @command{gcc} to compile the non-Ada part of your application, there are no Windows-specific restrictions that affect the overall interoperability with your Ada code. If you do want to use the Microsoft tools for your non-Ada code, you have two choices: @enumerate @item Encapsulate your non-Ada code in a DLL to be linked with your Ada application. In this case, use the Microsoft or whatever environment to build the DLL and use GNAT to build your executable (@pxref{Using DLLs with GNAT}). @item Or you can encapsulate your Ada code in a DLL to be linked with the other part of your application. In this case, use GNAT to build the DLL (@pxref{Building DLLs with GNAT Project files}) and use the Microsoft or whatever environment to build your executable. @end enumerate @node Windows Calling Conventions @section Windows Calling Conventions @findex Stdcall @findex APIENTRY This section pertain only to Win32. On Win64 there is a single native calling convention. All convention specifiers are ignored on this platform. @menu * C Calling Convention:: * Stdcall Calling Convention:: * Win32 Calling Convention:: * DLL Calling Convention:: @end menu @noindent When a subprogram @code{F} (caller) calls a subprogram @code{G} (callee), there are several ways to push @code{G}'s parameters on the stack and there are several possible scenarios to clean up the stack upon @code{G}'s return. A calling convention is an agreed upon software protocol whereby the responsibilities between the caller (@code{F}) and the callee (@code{G}) are clearly defined. Several calling conventions are available for Windows: @itemize @bullet @item @code{C} (Microsoft defined) @item @code{Stdcall} (Microsoft defined) @item @code{Win32} (GNAT specific) @item @code{DLL} (GNAT specific) @end itemize @node C Calling Convention @subsection @code{C} Calling Convention @noindent This is the default calling convention used when interfacing to C/C++ routines compiled with either @command{gcc} or Microsoft Visual C++. In the @code{C} calling convention subprogram parameters are pushed on the stack by the caller from right to left. The caller itself is in charge of cleaning up the stack after the call. In addition, the name of a routine with @code{C} calling convention is mangled by adding a leading underscore. The name to use on the Ada side when importing (or exporting) a routine with @code{C} calling convention is the name of the routine. For instance the C function: @smallexample int get_val (long); @end smallexample @noindent should be imported from Ada as follows: @smallexample @c ada @group function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (C, Get_Val, External_Name => "get_val"); @end group @end smallexample @noindent Note that in this particular case the @code{External_Name} parameter could have been omitted since, when missing, this parameter is taken to be the name of the Ada entity in lower case. When the @code{Link_Name} parameter is missing, as in the above example, this parameter is set to be the @code{External_Name} with a leading underscore. When importing a variable defined in C, you should always use the @code{C} calling convention unless the object containing the variable is part of a DLL (in which case you should use the @code{Stdcall} calling convention, @pxref{Stdcall Calling Convention}). @node Stdcall Calling Convention @subsection @code{Stdcall} Calling Convention @noindent This convention, which was the calling convention used for Pascal programs, is used by Microsoft for all the routines in the Win32 API for efficiency reasons. It must be used to import any routine for which this convention was specified. In the @code{Stdcall} calling convention subprogram parameters are pushed on the stack by the caller from right to left. The callee (and not the caller) is in charge of cleaning the stack on routine exit. In addition, the name of a routine with @code{Stdcall} calling convention is mangled by adding a leading underscore (as for the @code{C} calling convention) and a trailing @code{@@}@code{@var{nn}}, where @var{nn} is the overall size (in bytes) of the parameters passed to the routine. The name to use on the Ada side when importing a C routine with a @code{Stdcall} calling convention is the name of the C routine. The leading underscore and trailing @code{@@}@code{@var{nn}} are added automatically by the compiler. For instance the Win32 function: @smallexample @b{APIENTRY} int get_val (long); @end smallexample @noindent should be imported from Ada as follows: @smallexample @c ada @group function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val); -- On the x86 a long is 4 bytes, so the Link_Name is "_get_val@@4" @end group @end smallexample @noindent As for the @code{C} calling convention, when the @code{External_Name} parameter is missing, it is taken to be the name of the Ada entity in lower case. If instead of writing the above import pragma you write: @smallexample @c ada @group function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val, External_Name => "retrieve_val"); @end group @end smallexample @noindent then the imported routine is @code{_retrieve_val@@4}. However, if instead of specifying the @code{External_Name} parameter you specify the @code{Link_Name} as in the following example: @smallexample @c ada @group function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val, Link_Name => "retrieve_val"); @end group @end smallexample @noindent then the imported routine is @code{retrieve_val}, that is, there is no decoration at all. No leading underscore and no Stdcall suffix @code{@@}@code{@var{nn}}. @noindent This is especially important as in some special cases a DLL's entry point name lacks a trailing @code{@@}@code{@var{nn}} while the exported name generated for a call has it. @noindent It is also possible to import variables defined in a DLL by using an import pragma for a variable. As an example, if a DLL contains a variable defined as: @smallexample int my_var; @end smallexample @noindent then, to access this variable from Ada you should write: @smallexample @c ada @group My_Var : Interfaces.C.int; pragma Import (Stdcall, My_Var); @end group @end smallexample @noindent Note that to ease building cross-platform bindings this convention will be handled as a @code{C} calling convention on non-Windows platforms. @node Win32 Calling Convention @subsection @code{Win32} Calling Convention @noindent This convention, which is GNAT-specific is fully equivalent to the @code{Stdcall} calling convention described above. @node DLL Calling Convention @subsection @code{DLL} Calling Convention @noindent This convention, which is GNAT-specific is fully equivalent to the @code{Stdcall} calling convention described above. @node Introduction to Dynamic Link Libraries (DLLs) @section Introduction to Dynamic Link Libraries (DLLs) @findex DLL @noindent A Dynamically Linked Library (DLL) is a library that can be shared by several applications running under Windows. A DLL can contain any number of routines and variables. One advantage of DLLs is that you can change and enhance them without forcing all the applications that depend on them to be relinked or recompiled. However, you should be aware than all calls to DLL routines are slower since, as you will understand below, such calls are indirect. To illustrate the remainder of this section, suppose that an application wants to use the services of a DLL @file{API.dll}. To use the services provided by @file{API.dll} you must statically link against the DLL or an import library which contains a jump table with an entry for each routine and variable exported by the DLL. In the Microsoft world this import library is called @file{API.lib}. When using GNAT this import library is called either @file{libAPI.dll.a}, @file{libapi.dll.a}, @file{libAPI.a} or @file{libapi.a} (names are case insensitive). After you have linked your application with the DLL or the import library and you run your application, here is what happens: @enumerate @item Your application is loaded into memory. @item The DLL @file{API.dll} is mapped into the address space of your application. This means that: @itemize @bullet @item The DLL will use the stack of the calling thread. @item The DLL will use the virtual address space of the calling process. @item The DLL will allocate memory from the virtual address space of the calling process. @item Handles (pointers) can be safely exchanged between routines in the DLL routines and routines in the application using the DLL. @end itemize @item The entries in the jump table (from the import library @file{libAPI.dll.a} or @file{API.lib} or automatically created when linking against a DLL) which is part of your application are initialized with the addresses of the routines and variables in @file{API.dll}. @item If present in @file{API.dll}, routines @code{DllMain} or @code{DllMainCRTStartup} are invoked. These routines typically contain the initialization code needed for the well-being of the routines and variables exported by the DLL. @end enumerate @noindent There is an additional point which is worth mentioning. In the Windows world there are two kind of DLLs: relocatable and non-relocatable DLLs. Non-relocatable DLLs can only be loaded at a very specific address in the target application address space. If the addresses of two non-relocatable DLLs overlap and these happen to be used by the same application, a conflict will occur and the application will run incorrectly. Hence, when possible, it is always preferable to use and build relocatable DLLs. Both relocatable and non-relocatable DLLs are supported by GNAT. Note that the @option{-s} linker option (see GNU Linker User's Guide) removes the debugging symbols from the DLL but the DLL can still be relocated. As a side note, an interesting difference between Microsoft DLLs and Unix shared libraries, is the fact that on most Unix systems all public routines are exported by default in a Unix shared library, while under Windows it is possible (but not required) to list exported routines in a definition file (@pxref{The Definition File}). @node Using DLLs with GNAT @section Using DLLs with GNAT @menu * Creating an Ada Spec for the DLL Services:: * Creating an Import Library:: @end menu @noindent To use the services of a DLL, say @file{API.dll}, in your Ada application you must have: @enumerate @item The Ada spec for the routines and/or variables you want to access in @file{API.dll}. If not available this Ada spec must be built from the C/C++ header files provided with the DLL. @item The import library (@file{libAPI.dll.a} or @file{API.lib}). As previously mentioned an import library is a statically linked library containing the import table which will be filled at load time to point to the actual @file{API.dll} routines. Sometimes you don't have an import library for the DLL you want to use. The following sections will explain how to build one. Note that this is optional. @item The actual DLL, @file{API.dll}. @end enumerate @noindent Once you have all the above, to compile an Ada application that uses the services of @file{API.dll} and whose main subprogram is @code{My_Ada_App}, you simply issue the command @smallexample $ gnatmake my_ada_app -largs -lAPI @end smallexample @noindent The argument @option{-largs -lAPI} at the end of the @command{gnatmake} command tells the GNAT linker to look for an import library. The linker will look for a library name in this specific order: @enumerate @item @file{libAPI.dll.a} @item @file{API.dll.a} @item @file{libAPI.a} @item @file{API.lib} @item @file{libAPI.dll} @item @file{API.dll} @end enumerate The first three are the GNU style import libraries. The third is the Microsoft style import libraries. The last two are the DLL themself. Note that if the Ada package spec for @file{API.dll} contains the following pragma @smallexample @c ada pragma Linker_Options ("-lAPI"); @end smallexample @noindent you do not have to add @option{-largs -lAPI} at the end of the @command{gnatmake} command. If any one of the items above is missing you will have to create it yourself. The following sections explain how to do so using as an example a fictitious DLL called @file{API.dll}. @node Creating an Ada Spec for the DLL Services @subsection Creating an Ada Spec for the DLL Services @noindent A DLL typically comes with a C/C++ header file which provides the definitions of the routines and variables exported by the DLL. The Ada equivalent of this header file is a package spec that contains definitions for the imported entities. If the DLL you intend to use does not come with an Ada spec you have to generate one such spec yourself. For example if the header file of @file{API.dll} is a file @file{api.h} containing the following two definitions: @smallexample @group @cartouche int some_var; int get (char *); @end cartouche @end group @end smallexample @noindent then the equivalent Ada spec could be: @smallexample @c ada @group @cartouche with Interfaces.C.Strings; package API is use Interfaces; Some_Var : C.int; function Get (Str : C.Strings.Chars_Ptr) return C.int; private pragma Import (C, Get); pragma Import (DLL, Some_Var); end API; @end cartouche @end group @end smallexample @noindent Note that a variable is @strong{always imported with a DLL convention}. A function can have @code{C} or @code{Stdcall} convention. (@pxref{Windows Calling Conventions}). @node Creating an Import Library @subsection Creating an Import Library @cindex Import library @menu * The Definition File:: * GNAT-Style Import Library:: * Microsoft-Style Import Library:: @end menu @noindent If a Microsoft-style import library @file{API.lib} or a GNAT-style import library @file{libAPI.dll.a} or @file{libAPI.a} is available with @file{API.dll} you can skip this section. You can also skip this section if @file{API.dll} or @file{libAPI.dll} is built with GNU tools as in this case it is possible to link directly against the DLL. Otherwise read on. @node The Definition File @subsubsection The Definition File @cindex Definition file @findex .def @noindent As previously mentioned, and unlike Unix systems, the list of symbols that are exported from a DLL must be provided explicitly in Windows. The main goal of a definition file is precisely that: list the symbols exported by a DLL. A definition file (usually a file with a @code{.def} suffix) has the following structure: @smallexample @group @cartouche @r{[}LIBRARY @var{name}@r{]} @r{[}DESCRIPTION @var{string}@r{]} EXPORTS @var{symbol1} @var{symbol2} @dots{} @end cartouche @end group @end smallexample @table @code @item LIBRARY @var{name} This section, which is optional, gives the name of the DLL. @item DESCRIPTION @var{string} This section, which is optional, gives a description string that will be embedded in the import library. @item EXPORTS This section gives the list of exported symbols (procedures, functions or variables). For instance in the case of @file{API.dll} the @code{EXPORTS} section of @file{API.def} looks like: @smallexample @group @cartouche EXPORTS some_var get @end cartouche @end group @end smallexample @end table @noindent Note that you must specify the correct suffix (@code{@@}@code{@var{nn}}) (@pxref{Windows Calling Conventions}) for a Stdcall calling convention function in the exported symbols list. @noindent There can actually be other sections in a definition file, but these sections are not relevant to the discussion at hand. @node GNAT-Style Import Library @subsubsection GNAT-Style Import Library @noindent To create a static import library from @file{API.dll} with the GNAT tools you should proceed as follows: @enumerate @item Create the definition file @file{API.def} (@pxref{The Definition File}). For that use the @code{dll2def} tool as follows: @smallexample $ dll2def API.dll > API.def @end smallexample @noindent @code{dll2def} is a very simple tool: it takes as input a DLL and prints to standard output the list of entry points in the DLL. Note that if some routines in the DLL have the @code{Stdcall} convention (@pxref{Windows Calling Conventions}) with stripped @code{@@}@var{nn} suffix then you'll have to edit @file{api.def} to add it, and specify @option{-k} to @command{gnatdll} when creating the import library. @noindent Here are some hints to find the right @code{@@}@var{nn} suffix. @enumerate @item If you have the Microsoft import library (.lib), it is possible to get the right symbols by using Microsoft @code{dumpbin} tool (see the corresponding Microsoft documentation for further details). @smallexample $ dumpbin /exports api.lib @end smallexample @item If you have a message about a missing symbol at link time the compiler tells you what symbol is expected. You just have to go back to the definition file and add the right suffix. @end enumerate @item Build the import library @code{libAPI.dll.a}, using @code{gnatdll} (@pxref{Using gnatdll}) as follows: @smallexample $ gnatdll -e API.def -d API.dll @end smallexample @noindent @code{gnatdll} takes as input a definition file @file{API.def} and the name of the DLL containing the services listed in the definition file @file{API.dll}. The name of the static import library generated is computed from the name of the definition file as follows: if the definition file name is @var{xyz}@code{.def}, the import library name will be @code{lib}@var{xyz}@code{.a}. Note that in the previous example option @option{-e} could have been removed because the name of the definition file (before the ``@code{.def}'' suffix) is the same as the name of the DLL (@pxref{Using gnatdll} for more information about @code{gnatdll}). @end enumerate @node Microsoft-Style Import Library @subsubsection Microsoft-Style Import Library @noindent With GNAT you can either use a GNAT-style or Microsoft-style import library. A Microsoft import library is needed only if you plan to make an Ada DLL available to applications developed with Microsoft tools (@pxref{Mixed-Language Programming on Windows}). To create a Microsoft-style import library for @file{API.dll} you should proceed as follows: @enumerate @item Create the definition file @file{API.def} from the DLL. For this use either the @code{dll2def} tool as described above or the Microsoft @code{dumpbin} tool (see the corresponding Microsoft documentation for further details). @item Build the actual import library using Microsoft's @code{lib} utility: @smallexample $ lib -machine:IX86 -def:API.def -out:API.lib @end smallexample @noindent If you use the above command the definition file @file{API.def} must contain a line giving the name of the DLL: @smallexample LIBRARY "API" @end smallexample @noindent See the Microsoft documentation for further details about the usage of @code{lib}. @end enumerate @node Building DLLs with GNAT Project files @section Building DLLs with GNAT Project files @cindex DLLs, building @noindent There is nothing specific to Windows in the build process. @pxref{Library Projects}. @noindent Due to a system limitation, it is not possible under Windows to create threads when inside the @code{DllMain} routine which is used for auto-initialization of shared libraries, so it is not possible to have library level tasks in SALs. @node Building DLLs with GNAT @section Building DLLs with GNAT @cindex DLLs, building @noindent This section explain how to build DLLs using the GNAT built-in DLL support. With the following procedure it is straight forward to build and use DLLs with GNAT. @enumerate @item building object files The first step is to build all objects files that are to be included into the DLL. This is done by using the standard @command{gnatmake} tool. @item building the DLL To build the DLL you must use @command{gcc}'s @option{-shared} and @option{-shared-libgcc} options. It is quite simple to use this method: @smallexample $ gcc -shared -shared-libgcc -o api.dll obj1.o obj2.o @dots{} @end smallexample It is important to note that in this case all symbols found in the object files are automatically exported. It is possible to restrict the set of symbols to export by passing to @command{gcc} a definition file, @pxref{The Definition File}. For example: @smallexample $ gcc -shared -shared-libgcc -o api.dll api.def obj1.o obj2.o @dots{} @end smallexample If you use a definition file you must export the elaboration procedures for every package that required one. Elaboration procedures are named using the package name followed by "_E". @item preparing DLL to be used For the DLL to be used by client programs the bodies must be hidden from it and the .ali set with read-only attribute. This is very important otherwise GNAT will recompile all packages and will not actually use the code in the DLL. For example: @smallexample $ mkdir apilib $ copy *.ads *.ali api.dll apilib $ attrib +R apilib\*.ali @end smallexample @end enumerate At this point it is possible to use the DLL by directly linking against it. Note that you must use the GNAT shared runtime when using GNAT shared libraries. This is achieved by using @option{-shared} binder's option. @smallexample $ gnatmake main -Iapilib -bargs -shared -largs -Lapilib -lAPI @end smallexample @node Building DLLs with gnatdll @section Building DLLs with gnatdll @cindex DLLs, building @menu * Limitations When Using Ada DLLs from Ada:: * Exporting Ada Entities:: * Ada DLLs and Elaboration:: * Ada DLLs and Finalization:: * Creating a Spec for Ada DLLs:: * Creating the Definition File:: * Using gnatdll:: @end menu @noindent Note that it is preferred to use GNAT Project files (@pxref{Building DLLs with GNAT Project files}) or the built-in GNAT DLL support (@pxref{Building DLLs with GNAT}) or to build DLLs. This section explains how to build DLLs containing Ada code using @code{gnatdll}. These DLLs will be referred to as Ada DLLs in the remainder of this section. The steps required to build an Ada DLL that is to be used by Ada as well as non-Ada applications are as follows: @enumerate @item You need to mark each Ada @i{entity} exported by the DLL with a @code{C} or @code{Stdcall} calling convention to avoid any Ada name mangling for the entities exported by the DLL (@pxref{Exporting Ada Entities}). You can skip this step if you plan to use the Ada DLL only from Ada applications. @item Your Ada code must export an initialization routine which calls the routine @code{adainit} generated by @command{gnatbind} to perform the elaboration of the Ada code in the DLL (@pxref{Ada DLLs and Elaboration}). The initialization routine exported by the Ada DLL must be invoked by the clients of the DLL to initialize the DLL. @item When useful, the DLL should also export a finalization routine which calls routine @code{adafinal} generated by @command{gnatbind} to perform the finalization of the Ada code in the DLL (@pxref{Ada DLLs and Finalization}). The finalization routine exported by the Ada DLL must be invoked by the clients of the DLL when the DLL services are no further needed. @item You must provide a spec for the services exported by the Ada DLL in each of the programming languages to which you plan to make the DLL available. @item You must provide a definition file listing the exported entities (@pxref{The Definition File}). @item Finally you must use @code{gnatdll} to produce the DLL and the import library (@pxref{Using gnatdll}). @end enumerate @noindent Note that a relocatable DLL stripped using the @code{strip} binutils tool will not be relocatable anymore. To build a DLL without debug information pass @code{-largs -s} to @code{gnatdll}. This restriction does not apply to a DLL built using a Library Project. @pxref{Library Projects}. @node Limitations When Using Ada DLLs from Ada @subsection Limitations When Using Ada DLLs from Ada @noindent When using Ada DLLs from Ada applications there is a limitation users should be aware of. Because on Windows the GNAT run time is not in a DLL of its own, each Ada DLL includes a part of the GNAT run time. Specifically, each Ada DLL includes the services of the GNAT run time that are necessary to the Ada code inside the DLL. As a result, when an Ada program uses an Ada DLL there are two independent GNAT run times: one in the Ada DLL and one in the main program. It is therefore not possible to exchange GNAT run-time objects between the Ada DLL and the main Ada program. Example of GNAT run-time objects are file handles (e.g.@: @code{Text_IO.File_Type}), tasks types, protected objects types, etc. It is completely safe to exchange plain elementary, array or record types, Windows object handles, etc. @node Exporting Ada Entities @subsection Exporting Ada Entities @cindex Export table @noindent Building a DLL is a way to encapsulate a set of services usable from any application. As a result, the Ada entities exported by a DLL should be exported with the @code{C} or @code{Stdcall} calling conventions to avoid any Ada name mangling. As an example here is an Ada package @code{API}, spec and body, exporting two procedures, a function, and a variable: @smallexample @c ada @group @cartouche with Interfaces.C; use Interfaces; package API is Count : C.int := 0; function Factorial (Val : C.int) return C.int; procedure Initialize_API; procedure Finalize_API; -- Initialization & Finalization routines. More in the next section. private pragma Export (C, Initialize_API); pragma Export (C, Finalize_API); pragma Export (C, Count); pragma Export (C, Factorial); end API; @end cartouche @end group @end smallexample @smallexample @c ada @group @cartouche package body API is function Factorial (Val : C.int) return C.int is Fact : C.int := 1; begin Count := Count + 1; for K in 1 .. Val loop Fact := Fact * K; end loop; return Fact; end Factorial; procedure Initialize_API is procedure Adainit; pragma Import (C, Adainit); begin Adainit; end Initialize_API; procedure Finalize_API is procedure Adafinal; pragma Import (C, Adafinal); begin Adafinal; end Finalize_API; end API; @end cartouche @end group @end smallexample @noindent If the Ada DLL you are building will only be used by Ada applications you do not have to export Ada entities with a @code{C} or @code{Stdcall} convention. As an example, the previous package could be written as follows: @smallexample @c ada @group @cartouche package API is Count : Integer := 0; function Factorial (Val : Integer) return Integer; procedure Initialize_API; procedure Finalize_API; -- Initialization and Finalization routines. end API; @end cartouche @end group @end smallexample @smallexample @c ada @group @cartouche package body API is function Factorial (Val : Integer) return Integer is Fact : Integer := 1; begin Count := Count + 1; for K in 1 .. Val loop Fact := Fact * K; end loop; return Fact; end Factorial; @dots{} -- The remainder of this package body is unchanged. end API; @end cartouche @end group @end smallexample @noindent Note that if you do not export the Ada entities with a @code{C} or @code{Stdcall} convention you will have to provide the mangled Ada names in the definition file of the Ada DLL (@pxref{Creating the Definition File}). @node Ada DLLs and Elaboration @subsection Ada DLLs and Elaboration @cindex DLLs and elaboration @noindent The DLL that you are building contains your Ada code as well as all the routines in the Ada library that are needed by it. The first thing a user of your DLL must do is elaborate the Ada code (@pxref{Elaboration Order Handling in GNAT}). To achieve this you must export an initialization routine (@code{Initialize_API} in the previous example), which must be invoked before using any of the DLL services. This elaboration routine must call the Ada elaboration routine @code{adainit} generated by the GNAT binder (@pxref{Binding with Non-Ada Main Programs}). See the body of @code{Initialize_Api} for an example. Note that the GNAT binder is automatically invoked during the DLL build process by the @code{gnatdll} tool (@pxref{Using gnatdll}). When a DLL is loaded, Windows systematically invokes a routine called @code{DllMain}. It would therefore be possible to call @code{adainit} directly from @code{DllMain} without having to provide an explicit initialization routine. Unfortunately, it is not possible to call @code{adainit} from the @code{DllMain} if your program has library level tasks because access to the @code{DllMain} entry point is serialized by the system (that is, only a single thread can execute ``through'' it at a time), which means that the GNAT run time will deadlock waiting for the newly created task to complete its initialization. @node Ada DLLs and Finalization @subsection Ada DLLs and Finalization @cindex DLLs and finalization @noindent When the services of an Ada DLL are no longer needed, the client code should invoke the DLL finalization routine, if available. The DLL finalization routine is in charge of releasing all resources acquired by the DLL. In the case of the Ada code contained in the DLL, this is achieved by calling routine @code{adafinal} generated by the GNAT binder (@pxref{Binding with Non-Ada Main Programs}). See the body of @code{Finalize_Api} for an example. As already pointed out the GNAT binder is automatically invoked during the DLL build process by the @code{gnatdll} tool (@pxref{Using gnatdll}). @node Creating a Spec for Ada DLLs @subsection Creating a Spec for Ada DLLs @noindent To use the services exported by the Ada DLL from another programming language (e.g.@: C), you have to translate the specs of the exported Ada entities in that language. For instance in the case of @code{API.dll}, the corresponding C header file could look like: @smallexample @group @cartouche extern int *_imp__count; #define count (*_imp__count) int factorial (int); @end cartouche @end group @end smallexample @noindent It is important to understand that when building an Ada DLL to be used by other Ada applications, you need two different specs for the packages contained in the DLL: one for building the DLL and the other for using the DLL. This is because the @code{DLL} calling convention is needed to use a variable defined in a DLL, but when building the DLL, the variable must have either the @code{Ada} or @code{C} calling convention. As an example consider a DLL comprising the following package @code{API}: @smallexample @c ada @group @cartouche package API is Count : Integer := 0; @dots{} -- Remainder of the package omitted. end API; @end cartouche @end group @end smallexample @noindent After producing a DLL containing package @code{API}, the spec that must be used to import @code{API.Count} from Ada code outside of the DLL is: @smallexample @c ada @group @cartouche package API is Count : Integer; pragma Import (DLL, Count); end API; @end cartouche @end group @end smallexample @node Creating the Definition File @subsection Creating the Definition File @noindent The definition file is the last file needed to build the DLL. It lists the exported symbols. As an example, the definition file for a DLL containing only package @code{API} (where all the entities are exported with a @code{C} calling convention) is: @smallexample @group @cartouche EXPORTS count factorial finalize_api initialize_api @end cartouche @end group @end smallexample @noindent If the @code{C} calling convention is missing from package @code{API}, then the definition file contains the mangled Ada names of the above entities, which in this case are: @smallexample @group @cartouche EXPORTS api__count api__factorial api__finalize_api api__initialize_api @end cartouche @end group @end smallexample @node Using gnatdll @subsection Using @code{gnatdll} @findex gnatdll @menu * gnatdll Example:: * gnatdll behind the Scenes:: * Using dlltool:: @end menu @noindent @code{gnatdll} is a tool to automate the DLL build process once all the Ada and non-Ada sources that make up your DLL have been compiled. @code{gnatdll} is actually in charge of two distinct tasks: build the static import library for the DLL and the actual DLL. The form of the @code{gnatdll} command is @smallexample @cartouche @c $ gnatdll @ovar{switches} @var{list-of-files} @r{[}-largs @var{opts}@r{]} @c Expanding @ovar macro inline (explanation in macro def comments) $ gnatdll @r{[}@var{switches}@r{]} @var{list-of-files} @r{[}-largs @var{opts}@r{]} @end cartouche @end smallexample @noindent where @var{list-of-files} is a list of ALI and object files. The object file list must be the exact list of objects corresponding to the non-Ada sources whose services are to be included in the DLL. The ALI file list must be the exact list of ALI files for the corresponding Ada sources whose services are to be included in the DLL. If @var{list-of-files} is missing, only the static import library is generated. @noindent You may specify any of the following switches to @code{gnatdll}: @table @code @c @item -a@ovar{address} @c Expanding @ovar macro inline (explanation in macro def comments) @item -a@r{[}@var{address}@r{]} @cindex @option{-a} (@code{gnatdll}) Build a non-relocatable DLL at @var{address}. If @var{address} is not specified the default address @var{0x11000000} will be used. By default, when this switch is missing, @code{gnatdll} builds relocatable DLL. We advise the reader to build relocatable DLL. @item -b @var{address} @cindex @option{-b} (@code{gnatdll}) Set the relocatable DLL base address. By default the address is @code{0x11000000}. @item -bargs @var{opts} @cindex @option{-bargs} (@code{gnatdll}) Binder options. Pass @var{opts} to the binder. @item -d @var{dllfile} @cindex @option{-d} (@code{gnatdll}) @var{dllfile} is the name of the DLL. This switch must be present for @code{gnatdll} to do anything. The name of the generated import library is obtained algorithmically from @var{dllfile} as shown in the following example: if @var{dllfile} is @code{xyz.dll}, the import library name is @code{libxyz.dll.a}. The name of the definition file to use (if not specified by option @option{-e}) is obtained algorithmically from @var{dllfile} as shown in the following example: if @var{dllfile} is @code{xyz.dll}, the definition file used is @code{xyz.def}. @item -e @var{deffile} @cindex @option{-e} (@code{gnatdll}) @var{deffile} is the name of the definition file. @item -g @cindex @option{-g} (@code{gnatdll}) Generate debugging information. This information is stored in the object file and copied from there to the final DLL file by the linker, where it can be read by the debugger. You must use the @option{-g} switch if you plan on using the debugger or the symbolic stack traceback. @item -h @cindex @option{-h} (@code{gnatdll}) Help mode. Displays @code{gnatdll} switch usage information. @item -Idir @cindex @option{-I} (@code{gnatdll}) Direct @code{gnatdll} to search the @var{dir} directory for source and object files needed to build the DLL. (@pxref{Search Paths and the Run-Time Library (RTL)}). @item -k @cindex @option{-k} (@code{gnatdll}) Removes the @code{@@}@var{nn} suffix from the import library's exported names, but keeps them for the link names. You must specify this option if you want to use a @code{Stdcall} function in a DLL for which the @code{@@}@var{nn} suffix has been removed. This is the case for most of the Windows NT DLL for example. This option has no effect when @option{-n} option is specified. @item -l @var{file} @cindex @option{-l} (@code{gnatdll}) The list of ALI and object files used to build the DLL are listed in @var{file}, instead of being given in the command line. Each line in @var{file} contains the name of an ALI or object file. @item -n @cindex @option{-n} (@code{gnatdll}) No Import. Do not create the import library. @item -q @cindex @option{-q} (@code{gnatdll}) Quiet mode. Do not display unnecessary messages. @item -v @cindex @option{-v} (@code{gnatdll}) Verbose mode. Display extra information. @item -largs @var{opts} @cindex @option{-largs} (@code{gnatdll}) Linker options. Pass @var{opts} to the linker. @end table @node gnatdll Example @subsubsection @code{gnatdll} Example @noindent As an example the command to build a relocatable DLL from @file{api.adb} once @file{api.adb} has been compiled and @file{api.def} created is @smallexample $ gnatdll -d api.dll api.ali @end smallexample @noindent The above command creates two files: @file{libapi.dll.a} (the import library) and @file{api.dll} (the actual DLL). If you want to create only the DLL, just type: @smallexample $ gnatdll -d api.dll -n api.ali @end smallexample @noindent Alternatively if you want to create just the import library, type: @smallexample $ gnatdll -d api.dll @end smallexample @node gnatdll behind the Scenes @subsubsection @code{gnatdll} behind the Scenes @noindent This section details the steps involved in creating a DLL. @code{gnatdll} does these steps for you. Unless you are interested in understanding what goes on behind the scenes, you should skip this section. We use the previous example of a DLL containing the Ada package @code{API}, to illustrate the steps necessary to build a DLL. The starting point is a set of objects that will make up the DLL and the corresponding ALI files. In the case of this example this means that @file{api.o} and @file{api.ali} are available. To build a relocatable DLL, @code{gnatdll} does the following: @enumerate @item @code{gnatdll} builds the base file (@file{api.base}). A base file gives the information necessary to generate relocation information for the DLL. @smallexample @group $ gnatbind -n api $ gnatlink api -o api.jnk -mdll -Wl,--base-file,api.base @end group @end smallexample @noindent In addition to the base file, the @command{gnatlink} command generates an output file @file{api.jnk} which can be discarded. The @option{-mdll} switch asks @command{gnatlink} to generate the routines @code{DllMain} and @code{DllMainCRTStartup} that are called by the Windows loader when the DLL is loaded into memory. @item @code{gnatdll} uses @code{dlltool} (@pxref{Using dlltool}) to build the export table (@file{api.exp}). The export table contains the relocation information in a form which can be used during the final link to ensure that the Windows loader is able to place the DLL anywhere in memory. @smallexample @group $ dlltool --dllname api.dll --def api.def --base-file api.base \ --output-exp api.exp @end group @end smallexample @item @code{gnatdll} builds the base file using the new export table. Note that @command{gnatbind} must be called once again since the binder generated file has been deleted during the previous call to @command{gnatlink}. @smallexample @group $ gnatbind -n api $ gnatlink api -o api.jnk api.exp -mdll -Wl,--base-file,api.base @end group @end smallexample @item @code{gnatdll} builds the new export table using the new base file and generates the DLL import library @file{libAPI.dll.a}. @smallexample @group $ dlltool --dllname api.dll --def api.def --base-file api.base \ --output-exp api.exp --output-lib libAPI.a @end group @end smallexample @item Finally @code{gnatdll} builds the relocatable DLL using the final export table. @smallexample @group $ gnatbind -n api $ gnatlink api api.exp -o api.dll -mdll @end group @end smallexample @end enumerate @node Using dlltool @subsubsection Using @code{dlltool} @noindent @code{dlltool} is the low-level tool used by @code{gnatdll} to build DLLs and static import libraries. This section summarizes the most common @code{dlltool} switches. The form of the @code{dlltool} command is @smallexample @c $ dlltool @ovar{switches} @c Expanding @ovar macro inline (explanation in macro def comments) $ dlltool @r{[}@var{switches}@r{]} @end smallexample @noindent @code{dlltool} switches include: @table @option @item --base-file @var{basefile} @cindex @option{--base-file} (@command{dlltool}) Read the base file @var{basefile} generated by the linker. This switch is used to create a relocatable DLL. @item --def @var{deffile} @cindex @option{--def} (@command{dlltool}) Read the definition file. @item --dllname @var{name} @cindex @option{--dllname} (@command{dlltool}) Gives the name of the DLL. This switch is used to embed the name of the DLL in the static import library generated by @code{dlltool} with switch @option{--output-lib}. @item -k @cindex @option{-k} (@command{dlltool}) Kill @code{@@}@var{nn} from exported names (@pxref{Windows Calling Conventions} for a discussion about @code{Stdcall}-style symbols. @item --help @cindex @option{--help} (@command{dlltool}) Prints the @code{dlltool} switches with a concise description. @item --output-exp @var{exportfile} @cindex @option{--output-exp} (@command{dlltool}) Generate an export file @var{exportfile}. The export file contains the export table (list of symbols in the DLL) and is used to create the DLL. @item --output-lib @var{libfile} @cindex @option{--output-lib} (@command{dlltool}) Generate a static import library @var{libfile}. @item -v @cindex @option{-v} (@command{dlltool}) Verbose mode. @item --as @var{assembler-name} @cindex @option{--as} (@command{dlltool}) Use @var{assembler-name} as the assembler. The default is @code{as}. @end table @node GNAT and Windows Resources @section GNAT and Windows Resources @cindex Resources, windows @menu * Building Resources:: * Compiling Resources:: * Using Resources:: @end menu @noindent Resources are an easy way to add Windows specific objects to your application. The objects that can be added as resources include: @itemize @bullet @item menus @item accelerators @item dialog boxes @item string tables @item bitmaps @item cursors @item icons @item fonts @end itemize @noindent This section explains how to build, compile and use resources. @node Building Resources @subsection Building Resources @cindex Resources, building @noindent A resource file is an ASCII file. By convention resource files have an @file{.rc} extension. The easiest way to build a resource file is to use Microsoft tools such as @code{imagedit.exe} to build bitmaps, icons and cursors and @code{dlgedit.exe} to build dialogs. It is always possible to build an @file{.rc} file yourself by writing a resource script. It is not our objective to explain how to write a resource file. A complete description of the resource script language can be found in the Microsoft documentation. @node Compiling Resources @subsection Compiling Resources @findex rc @findex windres @cindex Resources, compiling @noindent This section describes how to build a GNAT-compatible (COFF) object file containing the resources. This is done using the Resource Compiler @code{windres} as follows: @smallexample $ windres -i myres.rc -o myres.o @end smallexample @noindent By default @code{windres} will run @command{gcc} to preprocess the @file{.rc} file. You can specify an alternate preprocessor (usually named @file{cpp.exe}) using the @code{windres} @option{--preprocessor} parameter. A list of all possible options may be obtained by entering the command @code{windres} @option{--help}. It is also possible to use the Microsoft resource compiler @code{rc.exe} to produce a @file{.res} file (binary resource file). See the corresponding Microsoft documentation for further details. In this case you need to use @code{windres} to translate the @file{.res} file to a GNAT-compatible object file as follows: @smallexample $ windres -i myres.res -o myres.o @end smallexample @node Using Resources @subsection Using Resources @cindex Resources, using @noindent To include the resource file in your program just add the GNAT-compatible object file for the resource(s) to the linker arguments. With @command{gnatmake} this is done by using the @option{-largs} option: @smallexample $ gnatmake myprog -largs myres.o @end smallexample @node Debugging a DLL @section Debugging a DLL @cindex DLL debugging @menu * Program and DLL Both Built with GCC/GNAT:: * Program Built with Foreign Tools and DLL Built with GCC/GNAT:: @end menu @noindent Debugging a DLL is similar to debugging a standard program. But we have to deal with two different executable parts: the DLL and the program that uses it. We have the following four possibilities: @enumerate 1 @item The program and the DLL are built with @code{GCC/GNAT}. @item The program is built with foreign tools and the DLL is built with @code{GCC/GNAT}. @item The program is built with @code{GCC/GNAT} and the DLL is built with foreign tools. @end enumerate @noindent In this section we address only cases one and two above. There is no point in trying to debug a DLL with @code{GNU/GDB}, if there is no GDB-compatible debugging information in it. To do so you must use a debugger compatible with the tools suite used to build the DLL. @node Program and DLL Both Built with GCC/GNAT @subsection Program and DLL Both Built with GCC/GNAT @noindent This is the simplest case. Both the DLL and the program have @code{GDB} compatible debugging information. It is then possible to break anywhere in the process. Let's suppose here that the main procedure is named @code{ada_main} and that in the DLL there is an entry point named @code{ada_dll}. @noindent The DLL (@pxref{Introduction to Dynamic Link Libraries (DLLs)}) and program must have been built with the debugging information (see GNAT -g switch). Here are the step-by-step instructions for debugging it: @enumerate 1 @item Launch @code{GDB} on the main program. @smallexample $ gdb -nw ada_main @end smallexample @item Start the program and stop at the beginning of the main procedure @smallexample (gdb) start @end smallexample @noindent This step is required to be able to set a breakpoint inside the DLL. As long as the program is not run, the DLL is not loaded. This has the consequence that the DLL debugging information is also not loaded, so it is not possible to set a breakpoint in the DLL. @item Set a breakpoint inside the DLL @smallexample (gdb) break ada_dll (gdb) cont @end smallexample @end enumerate @noindent At this stage a breakpoint is set inside the DLL. From there on you can use the standard approach to debug the whole program (@pxref{Running and Debugging Ada Programs}). @ignore @c This used to work, probably because the DLLs were non-relocatable @c keep this section around until the problem is sorted out. To break on the @code{DllMain} routine it is not possible to follow the procedure above. At the time the program stop on @code{ada_main} the @code{DllMain} routine as already been called. Either you can use the procedure below @pxref{Debugging the DLL Directly} or this procedure: @enumerate 1 @item Launch @code{GDB} on the main program. @smallexample $ gdb ada_main @end smallexample @item Load DLL symbols @smallexample (gdb) add-sym api.dll @end smallexample @item Set a breakpoint inside the DLL @smallexample (gdb) break ada_dll.adb:45 @end smallexample Note that at this point it is not possible to break using the routine symbol directly as the program is not yet running. The solution is to break on the proper line (break in @file{ada_dll.adb} line 45). @item Start the program @smallexample (gdb) run @end smallexample @end enumerate @end ignore @node Program Built with Foreign Tools and DLL Built with GCC/GNAT @subsection Program Built with Foreign Tools and DLL Built with GCC/GNAT @menu * Debugging the DLL Directly:: * Attaching to a Running Process:: @end menu @noindent In this case things are slightly more complex because it is not possible to start the main program and then break at the beginning to load the DLL and the associated DLL debugging information. It is not possible to break at the beginning of the program because there is no @code{GDB} debugging information, and therefore there is no direct way of getting initial control. This section addresses this issue by describing some methods that can be used to break somewhere in the DLL to debug it. @noindent First suppose that the main procedure is named @code{main} (this is for example some C code built with Microsoft Visual C) and that there is a DLL named @code{test.dll} containing an Ada entry point named @code{ada_dll}. @noindent The DLL (@pxref{Introduction to Dynamic Link Libraries (DLLs)}) must have been built with debugging information (see GNAT -g option). @node Debugging the DLL Directly @subsubsection Debugging the DLL Directly @enumerate 1 @item Find out the executable starting address @smallexample $ objdump --file-header main.exe @end smallexample The starting address is reported on the last line. For example: @smallexample main.exe: file format pei-i386 architecture: i386, flags 0x0000010a: EXEC_P, HAS_DEBUG, D_PAGED start address 0x00401010 @end smallexample @item Launch the debugger on the executable. @smallexample $ gdb main.exe @end smallexample @item Set a breakpoint at the starting address, and launch the program. @smallexample $ (gdb) break *0x00401010 $ (gdb) run @end smallexample The program will stop at the given address. @item Set a breakpoint on a DLL subroutine. @smallexample (gdb) break ada_dll.adb:45 @end smallexample Or if you want to break using a symbol on the DLL, you need first to select the Ada language (language used by the DLL). @smallexample (gdb) set language ada (gdb) break ada_dll @end smallexample @item Continue the program. @smallexample (gdb) cont @end smallexample @noindent This will run the program until it reaches the breakpoint that has been set. From that point you can use the standard way to debug a program as described in (@pxref{Running and Debugging Ada Programs}). @end enumerate @noindent It is also possible to debug the DLL by attaching to a running process. @node Attaching to a Running Process @subsubsection Attaching to a Running Process @cindex DLL debugging, attach to process @noindent With @code{GDB} it is always possible to debug a running process by attaching to it. It is possible to debug a DLL this way. The limitation of this approach is that the DLL must run long enough to perform the attach operation. It may be useful for instance to insert a time wasting loop in the code of the DLL to meet this criterion. @enumerate 1 @item Launch the main program @file{main.exe}. @smallexample $ main @end smallexample @item Use the Windows @i{Task Manager} to find the process ID. Let's say that the process PID for @file{main.exe} is 208. @item Launch gdb. @smallexample $ gdb @end smallexample @item Attach to the running process to be debugged. @smallexample (gdb) attach 208 @end smallexample @item Load the process debugging information. @smallexample (gdb) symbol-file main.exe @end smallexample @item Break somewhere in the DLL. @smallexample (gdb) break ada_dll @end smallexample @item Continue process execution. @smallexample (gdb) cont @end smallexample @end enumerate @noindent This last step will resume the process execution, and stop at the breakpoint we have set. From there you can use the standard approach to debug a program as described in (@pxref{Running and Debugging Ada Programs}). @node Setting Stack Size from gnatlink @section Setting Stack Size from @command{gnatlink} @noindent It is possible to specify the program stack size at link time. On modern versions of Windows, starting with XP, this is mostly useful to set the size of the main stack (environment task). The other task stacks are set with pragma Storage_Size or with the @command{gnatbind -d} command. Since older versions of Windows (2000, NT4, etc.) do not allow setting the reserve size of individual tasks, the link-time stack size applies to all tasks, and pragma Storage_Size has no effect. In particular, Stack Overflow checks are made against this link-time specified size. This setting can be done with @command{gnatlink} using either: @itemize @bullet @item using @option{-Xlinker} linker option @smallexample $ gnatlink hello -Xlinker --stack=0x10000,0x1000 @end smallexample This sets the stack reserve size to 0x10000 bytes and the stack commit size to 0x1000 bytes. @item using @option{-Wl} linker option @smallexample $ gnatlink hello -Wl,--stack=0x1000000 @end smallexample This sets the stack reserve size to 0x1000000 bytes. Note that with @option{-Wl} option it is not possible to set the stack commit size because the coma is a separator for this option. @end itemize @node Setting Heap Size from gnatlink @section Setting Heap Size from @command{gnatlink} @noindent Under Windows systems, it is possible to specify the program heap size from @command{gnatlink} using either: @itemize @bullet @item using @option{-Xlinker} linker option @smallexample $ gnatlink hello -Xlinker --heap=0x10000,0x1000 @end smallexample This sets the heap reserve size to 0x10000 bytes and the heap commit size to 0x1000 bytes. @item using @option{-Wl} linker option @smallexample $ gnatlink hello -Wl,--heap=0x1000000 @end smallexample This sets the heap reserve size to 0x1000000 bytes. Note that with @option{-Wl} option it is not possible to set the heap commit size because the coma is a separator for this option. @end itemize @end ifset @c ********************************** @c * GNU Free Documentation License * @c ********************************** @include fdl.texi @c GNU Free Documentation License @node Index,,GNU Free Documentation License, Top @unnumbered Index @printindex cp @contents @c Put table of contents at end, otherwise it precedes the "title page" in @c the .txt version @c Edit the pdf file to move the contents to the beginning, after the title @c page @bye