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+		   On Configuring Development Tools
+
+			K. Richard Pixley
+			Cygnus Support
+
+		 Last Mod Tue Oct 1 21:20:21 PDT 1991, by rich@cygnus.com
+
+INTRO
+-----
+
+    This document attempts to describe the general concepts behind
+    configuration of the Cygnus Support release of the GNU Development
+    Tools.  It also discusses common usage.  Eventually, FIXME, there
+    will also be a man page for "configure", an "info" tree, etc.
+
+
+BASICS
+------
+
+Some Basic Terms:
+
+    There are a lot of terms that are frequently used when discussing
+    development tools.  Most of the common terms have been used for
+    several different concepts such that their meanings have become
+    ambiguous to the point of being confusing.  Typically, we only
+    guess at their meanings from context and we frequently guess
+    wrong.
+
+    This document uses very few terms by comparison.  The intent is to
+    make the concepts as clear as possible in order to convey the
+    usage and intent of these tools.
+
+    "Programs" run on "machines".  Programs are very nearly always
+    written in "source".  Programs are "built" from source.
+    "Compilation" is a process that is frequently, but not always,
+    used when building programs.
+
+
+Host Environments:
+
+    In this document, the word "host" refers to the environment in
+    which this source will be compiled.  "host" and "host name" have
+    nothing to do with the proper name of your host, like "ucbvax",
+    "prep.ai.mit.edu" or "att.com".  Instead they refer to things like
+    "sun4" and "dec3100".
+
+    Forget for a moment that this particular directory of source is
+    the source for a development environment.  Instead, pretend that
+    it is the source for a simpler, more mundane, application, say, a
+    desk calculator.
+
+    Source that can be compiled in more than one environment,
+    generally needs to be set up for each environment explicitly.
+    Here we refer to that process as configuration.  That is, we
+    configure the source for a host.
+
+    For example, if we wanted to configure our mythical desk
+    calculator to compile on a SparcStation, we might configure for
+    host sun4.  With our configuration system:
+
+	cd desk-calculator ; ./configure sun4
+
+    does the trick.  "configure" is a shell script that sets up
+    Makefiles, subdirectories, and symbolic links appropriate for
+    compiling the source on a sun4.
+
+    The "host" environment does not necessarily refer to the machine
+    on which the tools are built.  It is possible to provide a sun3
+    development environment on a sun4.  If we wanted to use a cross
+    compiler on the sun4 to build a program intended to be run on a
+    sun3, we would configure the source for sun3.
+
+	cd desk-calculator ; ./configure sun3
+
+    The fact that we are actually building the program on a sun4 makes
+    no difference if the sun3 cross compiler presents an environment
+    that looks like a sun3 from the point of view of the desk
+    calculator source code.  Specifically, the environment is a sun3
+    environment if the header files, predefined symbols, and libraries
+    appear as they do on a sun3.
+
+    Nor does the host environment refer to the the machine on which
+    the program to be built will run.  It is possible to provide a
+    sun3 emulation environment on a sun4 such that programs built in a
+    sun3 development environment actually run on the sun4.
+
+    Host environment simply refers to the environment in which the
+    program will be built from the source.
+
+
+Configuration Time Options:
+
+    Many programs have compile time options.  That is, features of the
+    program that are either compiled into the program or not based on a
+    choice made by the person who builds the program.  We refer to these
+    as "configuration options".  For example, our desk calculator might be
+    capable of being compiled into a program that either uses infix
+    notation or postfix as a configuration option.  For a sun3, chosing
+    infix might be:
+
+	./configure sun3 +notation=infix
+
+    while a sun4 with postfix might be:
+
+	./configure sun4 +notation=postfix
+
+    If we wanted to build both at the same time, in the same directory
+    structure, the intermediate pieces used in the build process must
+    be kept separate.
+
+	./configure sun4 +subdirs +notation=postfix
+	./configure sun3 +subdirs +notation=infix
+
+    will create subdirectories for the intermediate pieces of the sun4
+    and sun3 configurations.  This is necessary as previous systems
+    were only capable of one configuration at a time.  A second
+    configuration overwrote the first.  We've chosen to retain this
+    behaviour so the "+subdirs" configuration option is necessary
+    to get the new behaviour.  The order of the arguments doesn't
+    matter.  There should be exactly one argument without a leading
+    '+' sign and that argument will be assumed to be the host name.
+
+    From here on the examples will assume that you want to build the
+    tools "in place" and won't show the "+subdirs" option, but
+    remember that it is available.
+
+    In order to actually install the program, the configuration system
+    needs to know where you would like the program installed.  The
+    default location is /usr/local.  We refer to this location as
+    $(destdir).  All user visible programs will be installed in
+    $(destdir)/bin.  All other programs and files will be installed in
+    a subdirectory of $(destdir)/lib.
+
+    You can elect to change $(destdir) only as a configuration time
+    option.
+
+	./configure sun4 +notation=postfix +destdir=/local
+
+    Will configure the source such that:
+
+	make install
+
+    will put it's programs in /local/bin and /local/lib/gcc.  If you
+    change $(destdir) after building the source, you will need to:
+
+	make clean
+
+    before the change will be propogated properly.  This is because
+    some tools need to know the locations of other tools.
+
+    With these concepts in mind, we can drop the desk calculator and
+    move on to the application that resides in these directories,
+    namely, the source to a development environment.
+
+
+SPECIFICS
+---------
+
+    The GNU Development Tools can be built on a wide variety of hosts.
+    So, of course, they must be configured.  Like the last example,
+
+	./configure sun4 +destdir=/local
+	./configure sun3 +destdir=/local
+
+    will configure the source to be built in subdirectories, in order
+    to keep the intermediate pieces separate, and to be installed in
+    /local.
+
+    When built with suitable development environments, these will be
+    native tools.  We'll explain the term "native" later.
+
+
+BUILDING DEVELOPMENT ENVIRONMENTS
+---------------------------------
+
+    The Cygnus Support GNU development tools can not only be built
+    with a number of host development environments, they can also be
+    configured to create a number of different development
+    environments on each of those hosts.  We refer to a specific
+    development environment created as a "target".  That is, the word
+    "target" refers to the development environment produced by
+    compiling this source and installing the resulting programs.
+
+    For the Cygnus Support GNU development tools, the default target
+    is the same as the host.  That is, the development environment
+    produced is intended to be compatible with the environment used to
+    build the tools.
+
+    In the example above, we created two configurations, one for sun4
+    and one for sun3.  The first configuration is expecting to be
+    built in a sun4 development environment, to create a sun4
+    development environment.  It doesn't necessarily need to be built
+    on a sun4 if a sun4 development environment is available
+    elsewhere.  Likewise, if the available sun4 development
+    environment produces executables intended for something other than
+    sun4, then the development environment built from this sun4
+    configuration will run on something other than a sun4.  From the
+    point of view of the configuration system and the GNU development
+    tools source, this doesn't matter.  What matters is that they will
+    be built in a sun4 environment.
+
+    Similarly, the second configuration given above is expecting to be
+    built in a sun3 development environment, to create a sun3
+    development environment.
+
+    The development environment produced, is a configuration time
+    option, just like $(destdir).
+
+	./configure sun4 +destdir=/local +target=sun3
+	./configure sun3 +destdir=/local +target=sun4
+
+    In this example, like before, we create two configurations.  The
+    first is intended to be built in a sun4 environment, in
+    subdirectories, to be installed in /local.  The second is intended
+    to be built in a sun3 environment, in subdirectories, to be
+    installed in /local.
+
+    Unlike the previous example, the first configuration will produce
+    a sun3 development environment, perhaps even suitable for building
+    the second configuration.  Likewise, the second configuration will
+    produce a sun4 development environment, perhaps even suitable for
+    building the first configuration.
+
+    The development environment used to build these configurations
+    will determine the machines on which the resulting development
+    environments can be used.
+
+
+A WALK THROUGH
+--------------
+
+Native Development Environments:
+
+    Let us assume for a moment that you have a sun4 and that with your
+    sun4 you received a development environment.  This development
+    environment is intended to be run on your sun4 to build programs
+    that can be run on your sun4.  You could, for instance, run this
+    development environment on your sun4 to build our example desk
+    calculator program.  You could then run the desk calculator
+    program on your sun4.
+
+    The resulting desk calculator program is referred to as a "native"
+    program.  The development environment itself is composed of native
+    programs that, when run, build other native programs.  Any other
+    program is referred to as "foreign".  Programs intended for other
+    machines are foreign programs.
+
+    This type of development environment, which is by far the most
+    common, is refered to as "native".  That is, a native development
+    environment runs on some machine to build programs for that same
+    machine.  The process of using a native development environment to
+    build native programs is called a "native" build.
+
+	./configure sun4
+
+    Will configure this source such that when built in a sun4
+    development environment, with a development environment that
+    builds programs intended to be run on sun4 machines, the programs
+    built will be native programs and the resulting development
+    environment will be a native development environment.
+
+    The development system that came with your sun4 is one such
+    environment.  Using it to build the GNU Development Tools is a
+    very common activity and the resulting development environment is
+    very popular.
+
+	make all
+
+    will build the tools as configured and will assume that you want
+    to use the native development environment that came with your
+    machine.
+
+    Using a development environment to build a development environment
+    is called "bootstrapping".  The Cygnus Support release of the GNU
+    Development Tools is capable of bootstrapping itself.  This is a
+    very powerful feature that we'll return to later.  For now, let's
+    pretend that you used the native development environment that came
+    with your sun4 to bootstrap the Cygnus Support release and let's
+    call the new development environment stage1.
+
+    Why bother?  Well, most people find that the Cygnus Support
+    release builds programs that run faster and take up less space
+    than the native development environments that came with their
+    machines.  Some people didn't get development environments with
+    their machines and some people just like using the GNU tools
+    better than using other tools.
+
+    While you're at it, if the GNU tools produce better programs, maybe
+    you should use them to build the GNU tools.  It's a good idea, so
+    let's pretend that you do.  Let's call the new development
+    environment stage2.
+
+    So far you've built a development environment, stage1, and you've
+    used stage1 to build a new, faster and smaller development
+    environment, stage2, but you haven't run any of the programs that
+    the GNU tools have built.  You really don't yet know if these
+    tools work.  Do you have any programs built with the GNU tools?
+    Yes, you do.  stage2.  What does that program do?  It builds
+    programs.  Ok, do you have any source handy to build into a
+    program?  Yes, you do.  The GNU tools themselves.  In fact, if you
+    use stage2 to build the GNU tools again the resulting programs
+    should be identical to stage2.  Let's pretend that you do and call
+    the new development environment stage3.
+
+    You've just completed what's called a "three stage boot".  You now
+    have a small, fast, somewhat tested, development environment.
+
+	make bootstrap
+
+    will do a three stage boot across all tools and will compare
+    stage2 to stage3 and complain if they are not identical.
+
+    Once built,
+
+	make install
+
+    will install the development environment in the default location
+    or in $(destdir) if you specified an alternate when you
+    configured.  In fact, you can skip the "make all" part and just
+    "make install" which will make sure that the development
+    environment is built before attempting to install anything.  Even
+    better, for configurations where host is the same as target, like
+    this one, "make install" will make sure that a "make bootstrap" is
+    done before installing anything.
+
+    Any development environment that is not a native development
+    environment is refered to as a "cross" development environment.
+    There are many different types of cross development environments
+    but most fall into one of FIXME basic categories.
+
+
+Emulation Environments:
+
+    The first category of cross development environment is called
+    "emulation".  There are two primary types of emulation, but both
+    types result in programs that run on the native host.
+
+    The first type is "software emulation".  This form of cross
+    development environment involves a native program that when run on
+    the native host, is capable of interpreting, and in most aspects
+    running, a program intended for some other machine.  This
+    technique is typically used when the other machine is either too
+    expensive, too slow, too fast, or not available, perhaps because
+    it hasn't yet been built.  The native, interpreting program is
+    called a "software emulator".
+
+    The GNU Development Tools do not currently include any software
+    emulators.  Some do exist and the GNU Development Tools can be
+    configured to create simple cross development environments for
+    with these emulators.  More on this later.
+
+    The second type of emulation is when source intended for some
+    other development environment is built into a program intended for
+    the native host.  The concept of universes in operating systems
+    and hosted operating systems are two such development
+    environments.
+
+    The Cygnus Support Release of the GNU Development Tools can be
+    configured for one such emulation at this time.
+
+	./configure sun4 +ansi
+
+    will configure the source such that when built in a sun4
+    development environment the resulting development environment is
+    capable of building sun4 programs from strictly conforming ANSI
+    X3J11 C source.  Remember that the environment used to build the
+    tools determines the machine on which this tools will run, so the
+    resulting programs aren't necessarily intended to run on a sun4,
+    although they usually are.  Also note that the source for the GNU
+    tools is not strictly conforming ANSI source so this configuration
+    cannot be used to bootstrap the GNU tools.
+
+
+Simple Cross Environments:
+
+	./configure sun4 +target=a29k
+
+    will configure the tools such that when compiled in a sun4
+    development environment the resulting development environment can
+    be used to create programs intended for an a29k.  Again, this does
+    not necessarily mean that the new development environment can be
+    run on a sun4.  That would depend on the development environment
+    used to build these tools.
+
+    Earlier you saw how to configure the tools to build a native
+    development environment, that is, a development environment that
+    runs on your sun4 and builds programs for your sun4.  Let's
+    pretend that you use stage3 to build this simple cross
+    configuration and let's call the new development environment
+    gcc-a29k.  Remember that this is a native build.  Gcc-a29k is a
+    collection of native programs intended to run on your sun4.
+    That's what stage3 builds, programs for your sun4.  Gcc-a29k
+    represents an a29k development environment that builds programs
+    intended to run on an a29k.  But, remember, gcc-a29k runs on your
+    sun4.  Programs built with gcc-a29k will run on your sun4 only
+    with the help of an appropriate software emulator.
+
+    Building gcc-a29k is also a bootstrap but of a slightly different
+    sort.  We call gcc-a29k a simple cross environment and using
+    gcc-a29k to build a program intended for a29k is called "crossing
+    to" a29k.  Simple cross environments are the second category of
+    cross development environments.
+
+
+Crossing Into Targets:
+
+	./configure a29k +target=a29k
+
+    will configure the tools such that when compiled in an a29k
+    development environment, the resulting development environment can
+    be used to create programs intended for an a29k.  Again, this does
+    not necessarily mean that the new development environment can be
+    run on an a29k.  That would depend on the development environment
+    used to build these tools.
+
+    If you've been following along this walk through, then you've
+    already built an a29k environment, namely gcc-a29k.  Let's pretend
+    you use gcc-a29k to build the current configuration.
+
+    Gcc-a29k builds programs intended for the a29k so the new
+    development environment will be intended for use on an a29k.  That
+    is, this new gcc consists of programs that are foreign to your
+    sun4.  They cannot be run on your sun4.
+
+    The process of building this configuration is another a bootstrap.
+    This bootstrap is also a cross to a29k.  Because this type of
+    build is both a bootstrap and a cross to a29k, it is sometimes
+    referred to as a "cross into" a29k.  This new development
+    environment isn't really a cross development environment at all.
+    It is intended to run on an a29k to produce programs for an a29k.
+    You'll remember that this makes it, by definition, an a29k native
+    compiler.  "Crossing into" has been introduced here not because it
+    is a type of cross development environment, but because it is
+    frequently confused one.  The process is "a cross" but the
+    resulting development environment is a native development
+    environment.
+
+    You could not have built this configuration with stage3, because
+    stage3 doesn't provide an a29k environment.  Instead it provides a
+    sun4 environment.
+
+    If you happen to have an a29k lying around, you could now use
+    this fresh development environment on the a29k to three-stage
+    these tools all over again.  This process would look just like it
+    did when we built the native sun4 development environment because
+    we would be building another native development environment, this
+    one on a29k.
+
+    
+The Three Party Cross:
+
+    So far you've seen that our development environment source must be
+    configured for a specific host and for a specific target.  You've
+    also seen that the resulting development environment depends on
+    the development environment used in the build process.
+
+    When all four match identically, that is, the configured host, the
+    configured target, the environment presented by the development
+    environment used in the build, and the machine on which the
+    resulting development environment is intended to run, then the new
+    development environment will be a native development environment.
+
+    When all four match except the configured host, then we can assume
+    that the development environment used in the build is some form of
+    library emulation.
+
+    When all four match except for the configured target, then the
+    resulting development environment will be a simple cross
+    development environment.
+
+    When all four match except for the host on which the development
+    environment used in the build runs, the build process is a "cross
+    into" and the resulting development environment will be native to
+    some other machine.
+
+    Most of the other permutations do exist in some form, but only one
+    more is interesting to the current discussion.
+
+	./configure a29k +target=sun3
+
+    will configure the tools such that when compiled in an a29k
+    development environment, the resulting development environment can
+    be used to create programs intended for a sun3.  Again, this does
+    not necessarily mean that the new development environment can be
+    run on an a29k.  That would depend on the development environment
+    used to build these tools.
+
+    If you are still following along, then you have two a29k
+    development environments, the native development environment that
+    runs on a29k, and the simple cross that runs on your sun4.  If you
+    use the a29k native development environment on the a29k, you will
+    be doing the same thing we did a while back, namely building a
+    simple cross from a29k to sun3.  Let's pretend that instead, you
+    use gcc-a29k, the simple cross development environment that runs
+    on sun4 but produces programs for a29k.
+
+    The resulting development environment will run on a29k because
+    that's what gcc-a29k builds, a29k programs.  This development
+    environment will produce programs for a sun3 because that is how
+    it was configured.  This means that the resulting development
+    environment is a simple cross.
+
+    There really isn't a common name for this process because very few
+    development environments are capable of being configured this
+    extensively.  For the sake of discussion, let's call this process
+    a "three party cross".
+
+
+FINAL NOTES
+-----------
+
+By "configures", I mean that links, Makefile, .gdbinit, and
+config.status are built.  Configuration is always done from the source
+directory.
+
+* "./configure name" configures this directory, perhaps recursively,
+  for a single host+target pair where the host and target are both
+  "name".  If a previous configuration existed, it will be
+  overwritten.
+
+* "./configure hostname +target=targetname" configures this directory,
+  perhaps recursively, for a single host+target pair where the host is
+  hostname and target is targetname.  If a previous configuration
+  existed, it will be overwritten.
+
+* "./configure +subdirs hostname +target=targetname" creates a
+  subdirectories H-hostname and H-hostname/T-targetname and
+  configures H-hostname/T-targetname.  For now, makes should
+  be done from H-hostname/T-targetname.  "./configure +sub name"
+  works as expected.  That is, it creates H-name and
+  H-name/T-name and configures the latter.
+
+
+Hacking configurations:
+
+The configure scripts essentially do three things, create
+subdirectories if appropriate, build a Makefile, and create links to
+files, all based on and tailored to, a specific host+target pair.  The
+scripts also create a .gdbinit if appropriate but this is not
+tailored.
+
+The Makefile is created by prepending some variable definitions to a
+Makefile template called Makefile.in and then inserting host and
+target specific Makefile fragments.  The variables are set based on
+the chosen host+target pair and build style, that is, if you use
+subdirectories or not.  The host and target specific Makefile may or
+may not exist.  If fragments
+
+* Makefiles can be edited directly, but those changes will eventually
+  be lost.  Changes intended to be permanent for a specific host
+  should be made to the host specific Makefile fragment.  This should
+  be in ./config/hmake-host if it exists.  Changes intended to be
+  permanent for a specific target should be made to the target
+  specific Makefile fragment.  This should be in ./config/tmake-target
+  if it exists.  Changes intended to be permanent for the directory
+  should be made in Makefile.in.  To propogate changes to any of
+  these, either use "make Makefile" or re-configure from the source
+  directory.
+
+* configure can be edited directly, but those changes will eventually
+  be lost.  Changes intended to be permanent for a specific directory
+  should be made to configure.in.  Changes intended to be permanent
+  for all configure scripts should be made to configure.template.
+  Propogating changes to configure.in requires the presence of
+  configure.template which normally resides in the uppermost directory
+  you received.  To propogate changes to either configure.template or
+  a configure.in, use "configure +template=pathtothetemplate".
+  This will configure the configure scripts themselves, recursively if
+  appropriate.
+
+* "./configure -srcdir=foo" is not supported yet.  At the moment, things
+  will probably be configured correctly only for leaf directories, and
+  even they will not have paths to libraries set properly.