--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2008-03-10  Peter O'Gorman  <bug-gnulib@mlists.thewrittenword.com>
+            Bruno Haible  <bruno@clisp.org>
+
+	Make va_copy work with some version of xlc on AIX 5.1.
+	* lib/stdarg.in.h: New file.
+	* m4/stdarg.m4 (gl_STDARG_H): Initialize STDARG_H and NEXT_STDARG_H.
+	On AIX, use a <stdarg.h> file substitute.
+	* modules/stdarg (Files): Add lib/stdarg.in.h.
+	(Depends-on): Add include_next.
+	(Makefile.am): Build a stdarg.h substitute if requested.
+	* doc/posix-functions/va_copy.texi: Document the platforms lacking it.
+
 2008-03-10  Bruno Haible  <bruno@clisp.org>
 
 	* m4/include_next.m4 (gl_CHECK_NEXT_HEADERS): Document a restriction.

--- a/doc/posix-functions/va_copy.texi
+++ b/doc/posix-functions/va_copy.texi
@@ -9,7 +9,8 @@
 Portability problems fixed by Gnulib:
 @itemize
 @item
-This macro is missing on some platforms.
+This macro is missing on some platforms:
+AIX 5.1 with cc or xlc, HP-UX 11 with cc, IRIX 6.5 with cc, OSF/1 5.1 with cc.
 @end itemize
 
 Portability problems not fixed by Gnulib:

--- a/m4/stdarg.m4
+++ b/m4/stdarg.m4
@@ -1,5 +1,5 @@
-# stdarg.m4 serial 1
-dnl Copyright (C) 2006 Free Software Foundation, Inc.
+# stdarg.m4 serial 2
+dnl Copyright (C) 2006, 2008 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
@@ -9,6 +9,8 @@
 
 AC_DEFUN([gl_STDARG_H],
 [
+  STDARG_H='';                AC_SUBST([STDARG_H])
+  NEXT_STDARG_H='<stdarg.h>'; AC_SUBST([NEXT_STDARG_H])
   AC_MSG_CHECKING([for va_copy])
   AC_CACHE_VAL([gl_cv_func_va_copy], [
     AC_TRY_COMPILE([#include <stdarg.h>], [
@@ -19,22 +21,47 @@
       [gl_cv_func_va_copy=yes], [gl_cv_func_va_copy=no])])
   AC_MSG_RESULT([$gl_cv_func_va_copy])
   if test $gl_cv_func_va_copy = no; then
-    # Provide a substitute, either __va_copy or as a simple assignment.
-    AC_CACHE_VAL([gl_cv_func___va_copy], [
-      AC_TRY_COMPILE([#include <stdarg.h>], [
+    dnl Provide a substitute.
+    dnl Usually a simple definition in <config.h> is enough. Not so on AIX 5
+    dnl with some versions of the /usr/vac/bin/cc compiler. It has an <stdarg.h>
+    dnl which does '#undef va_copy', leading to a missing va_copy symbol. For
+    dnl this platform, we use an <stdarg.h> substitute. But we cannot use this
+    dnl approach on other platforms, because <stdarg.h> often defines only
+    dnl preprocessor macros and gl_ABSOLUTE_HEADER, gl_CHECK_NEXT_HEADERS do
+    dnl not work in this situation.
+    AC_EGREP_CPP([vaccine],
+      [#if defined _AIX && !defined __GNUC__
+        AIX vaccine
+       #endif
+      ], [gl_aixcc=yes], [gl_aixcc=no])
+    if test $gl_aixcc = yes; then
+      dnl Provide a substitute <stdarg.h> file.
+      STDARG_H=stdarg.h
+      gl_CHECK_NEXT_HEADERS([stdarg.h])
+      dnl Fallback for the case when <stdarg.h> contains only macro definitions.
+      if test "$gl_cv_next_stdarg_h" = '""'; then
+        gl_cv_next_stdarg_h='"///usr/include/stdarg.h"'
+        NEXT_STDARG_H="$gl_cv_next_stdarg_h"
+      fi
+    else
+      dnl Provide a substitute in <config.h>, either __va_copy or as a simple
+      dnl assignment.
+      AC_CACHE_VAL([gl_cv_func___va_copy], [
+        AC_TRY_COMPILE([#include <stdarg.h>], [
 #ifndef __va_copy
 error, bail out
 #endif
 ],
-        [gl_cv_func___va_copy=yes], [gl_cv_func___va_copy=no])])
-    if test $gl_cv_func___va_copy = yes; then
-      AC_DEFINE([va_copy], [__va_copy],
-        [Define as a macro for copying va_list variables.])
-    else
-      AH_VERBATIM([gl_VA_COPY], [/* A replacement for va_copy, if needed.  */
+          [gl_cv_func___va_copy=yes], [gl_cv_func___va_copy=no])])
+      if test $gl_cv_func___va_copy = yes; then
+        AC_DEFINE([va_copy], [__va_copy],
+          [Define as a macro for copying va_list variables.])
+      else
+        AH_VERBATIM([gl_VA_COPY], [/* A replacement for va_copy, if needed.  */
 #define gl_va_copy(a,b) ((a) = (b))])
-      AC_DEFINE([va_copy], [gl_va_copy],
-        [Define as a macro for copying va_list variables.])
+        AC_DEFINE([va_copy], [gl_va_copy],
+          [Define as a macro for copying va_list variables.])
+      fi
     fi
   fi
 ])

--- a/modules/stdarg
+++ b/modules/stdarg
@@ -2,9 +2,11 @@
 An <stdarg.h> that conforms to C99.
 
 Files:
+lib/stdarg.in.h
 m4/stdarg.m4
 
 Depends-on:
+include_next
 
 configure.ac-early:
 dnl Some compilers (e.g., AIX 5.3 cc) need to be in c99 mode
@@ -17,6 +19,19 @@
 gl_STDARG_H
 
 Makefile.am:
+BUILT_SOURCES += $(STDARG_H)
+
+# We need the following in order to create <stdarg.h> when the system
+# doesn't have one that works with the given compiler.
+stdarg.h: stdarg.in.h
+	rm -f $@-t $@
+	{ echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */' && \
+	  sed -e 's/@''INCLUDE_NEXT''@/$(INCLUDE_NEXT)/g' \
+	      -e 's|@''NEXT_STDARG_H''@|$(NEXT_STDARG_H)|g' \
+	      < $(srcdir)/stdarg.in.h; \
+	} > $@-t
+	mv $@-t $@
+MOSTLYCLEANFILES += stdarg.h stdarg.h-t
 
 Include:
 #include <stdarg.h>