[doc,committed] fix PR c/80409

Message ID 9dcba733-0b8b-91c4-7922-54a45e536d0e@codesourcery.com
State New
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  • [doc,committed] fix PR c/80409
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Sandra Loosemore Feb. 26, 2019, 2:36 a.m.
I've checked in this patch to document the GNU extension to va_arg for 
pointer types, which is really a POSIX extension per discussion in the 
issue.

-Sandra

Patch

Index: gcc/doc/extend.texi
===================================================================
--- gcc/doc/extend.texi	(revision 269202)
+++ gcc/doc/extend.texi	(working copy)
@@ -47,6 +47,7 @@  extensions, accepted by GCC in C90 mode
 * Escaped Newlines::    Slightly looser rules for escaped newlines.
 * Subscripting::        Any array can be subscripted, even if not an lvalue.
 * Pointer Arith::       Arithmetic on @code{void}-pointers and function pointers.
+* Variadic Pointer Args::  Pointer arguments to variadic functions.
 * Pointers to Arrays::  Pointers to arrays with qualifiers work as expected.
 * Initializers::        Non-constant initializers.
 * Compound Literals::   Compound literals give structures, unions
@@ -1944,6 +1945,22 @@  and on function types, and returns 1.
 The option @option{-Wpointer-arith} requests a warning if these extensions
 are used.
 
+@node Variadic Pointer Args
+@section Pointer Arguments in Variadic Functions
+@cindex pointer arguments in variadic functions
+@cindex variadic functions, pointer arguments
+
+Standard C requires that pointer types used with @code{va_arg} in
+functions with variable argument lists either must be compatible with
+that of the actual argument, or that one type must be a pointer to
+@code{void} and the other a pointer to a character type.  GNU C
+implements the POSIX XSI extension that additionally permits the use
+of @code{va_arg} with a pointer type to receive arguments of any other
+pointer type.
+
+In particular, in GNU C @samp{va_arg (ap, void *)} can safely be used
+to consume an argument of any pointer type.
+
 @node Pointers to Arrays
 @section Pointers to Arrays with Qualifiers Work as Expected
 @cindex pointers to arrays