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
2019-02-25 Sandra Loosemore <san...@codesourcery.com>
PR c/80409
gcc/
* doc/extend.texi (Variadic Pointer Args): New section.
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
