diff options
Diffstat (limited to 'gcc/doc/extend.texi')
| -rw-r--r-- | gcc/doc/extend.texi | 40 |
1 files changed, 35 insertions, 5 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 4209f2a5dbc..301db237124 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -1869,6 +1869,7 @@ the enclosing block. @cindex @code{volatile} applied to function @cindex @code{const} applied to function @cindex functions with @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style arguments +@cindex functions with non-null pointer arguments @cindex functions that are passed arguments in registers on the 386 @cindex functions that pop the argument stack on the 386 @cindex functions that do not pop the argument stack on the 386 @@ -1885,11 +1886,11 @@ attributes are currently defined for functions on all targets: @code{pure}, @code{const}, @code{format}, @code{format_arg}, @code{no_instrument_function}, @code{section}, @code{constructor}, @code{destructor}, @code{used}, -@code{unused}, @code{deprecated}, @code{weak}, @code{malloc}, and -@code{alias}. Several other attributes are defined for functions on -particular target systems. Other attributes, including @code{section} -are supported for variables declarations (@pxref{Variable Attributes}) -and for types (@pxref{Type Attributes}). +@code{unused}, @code{deprecated}, @code{weak}, @code{malloc}, +@code{alias}, and @code{nonnull}. Several other attributes are defined +for functions on particular target systems. Other attributes, including +@code{section} are supported for variables declarations +(@pxref{Variable Attributes}) and for types (@pxref{Type Attributes}). You may also specify attributes with @samp{__} preceding and following each keyword. This allows you to use them in header files without @@ -2101,6 +2102,35 @@ requested by @option{-ansi} or an appropriate @option{-std} option, or @option{-ffreestanding} is used. @xref{C Dialect Options,,Options Controlling C Dialect}. +@item nonnull (@var{arg-index,...}) +@cindex @code{nonnull} function attribute +The @code{nonnull} attribute specifies that some function parameters should +be non-null pointers. For instance, the declaration: + +@smallexample +extern void * +my_memcpy (void *dest, const void *src, size_t len) + __attribute__((nonnull (1, 2))); +@end smallexample + +@noindent +causes the compiler to check that, in calls to @code{my_memcpy}, +arguments @var{dest} and @var{src} are non-null. If the compiler +determines that a null pointer is passed in an argument slot marked +as non-null, and the @option{-Wnonnull} option is enabled, a warning +is issued. The compiler may also choose to make optimizations based +on the knowledge that certain function arguments will not be null. + +If no argument index list is given to the @code{nonnull} attribute, +all pointer arguments are marked as non-null. To illustrate, the +following declaration is equivalent to the previous example: + +@smallexample +extern void * +my_memcpy (void *dest, const void *src, size_t len) + __attribute__((nonnull)); +@end smallexample + @item no_instrument_function @cindex @code{no_instrument_function} function attribute @opindex finstrument-functions |
