--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,65 @@
+2011-02-12  Paul Eggert  <eggert@cs.ucla.edu>
+
+	stdlib: support non-GCC __attribute__
+
+	Fix a serious and tricky problem encountered when attempting to
+	add the getloadavg module to Emacs.  Emacs worked fine on RHEL
+	5.5, but it crashed due to memory corruption on Solaris 10 with
+	Sun C 5.11.  Emacs normally ORs 3-bit tags into their low-order
+	bits that are otherwise zero.  This tagging is optional inside
+	Emacs but is preferred and is used when __attribute__ ((__aligned
+	(8))) works, as it does with both recent-enough GCC and with Sun C
+	5.11.  However, Sun C 5.11 is not GCC and does not #define
+	__GNUC__ and __GNUC_MINOR__.
+
+	When I added the getloadavg module to Emacs, it brought in
+	stdlib.in.h, which contained this fragment:
+
+	   #ifndef __attribute__
+	   # if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 8)
+	   #  define __attribute__(Spec)   /* empty */
+	   # endif
+	   #endif
+
+	When files that include <stdlib.h> were compiled with Sun C 5.11,
+	the above code disabled __attribute__ ((__aligned (8))), which
+	caused variables to not be properly aligned, which eventually led
+	to the pointer corruption mentioned above.  (This was a bit hard
+	to diagnose, unfortunately.)
+
+	Several "#define __attribute__(X) /* empty */" code snippets need
+	to be eradicated from Gnulib to work with non-GCC compilers that
+	support __attribute__.  The Autoconf way to do this is to test for
+	each kind of attribute that we want support for, and selectively
+	enable that in source code.
+
+	Fix this problem just for stdlib.h, by adding a test for the
+	__noreturn__ attribute, and change stdlib.in.h to use that test
+	when needed.  This technique can be easily generalized to the
+	other *.in.h files and attributes, and a similar technique can be
+	used for *.h and *.c files.  This patch is enough to solve the
+	problem for Emacs + getloadavg, and I thought I'd publish it for
+	feedback before undertaking further, similar fixes in other
+	modules.
+
+	This patch does not arrange to #define HAVE_ATTRIBUTE_NORETURN
+	because it's not needed for stdlib.h.  It merely substitutes the
+	value directly into stdlib.h.  We may well need to #define it, or
+	similar symbols, for other modules, but it's nice to also have an
+	option to not #define it for applications like Emacs that do not
+	need it.
+
+	* lib/stdlib.in.h (__attribute__): Do not #define.
+	(_GL_ATTRIBUTE_NORETURN): New macro, which in stdlib.h needs to
+	be defined only if the _Exit module is also used.
+	* m4/_Exit.m4 (gl_FUNC__EXIT): Require gl_ATTRIBUTE_NORETURN.
+	* m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Subst
+	HAVE_ATTRIBUTE_NORETURN and default it to 1, its value on GNU
+	platforms.
+	* modules/_Exit (Files): Add m4/attribute.m4.
+	* modules/stdlib (Makefile.am): Substitute HAVE_ATTRIBUTE_NORETURN.
+	* m4/attribute.m4: New file.
+
 2011-02-12  Bruno Haible  <bruno@clisp.org>
 
 	wcsrtombs: Work around bug on native Windows.

--- a/lib/stdlib.in.h
+++ b/lib/stdlib.in.h
@@ -88,12 +88,6 @@
 # include <unistd.h>
 #endif
 
-#ifndef __attribute__
-# if __GNUC__ < 2 || (__GNUC__ == 2 && __GNUC_MINOR__ < 8)
-#  define __attribute__(Spec)   /* empty */
-# endif
-#endif
-
 /* The definitions of _GL_FUNCDECL_RPL etc. are copied here.  */
 
 /* The definition of _GL_ARG_NONNULL is copied here.  */
@@ -119,7 +113,12 @@
 /* Terminate the current process with the given return code, without running
    the 'atexit' handlers.  */
 # if !@HAVE__EXIT@
-_GL_FUNCDECL_SYS (_Exit, void, (int status) __attribute__ ((__noreturn__)));
+#  if @HAVE_ATTRIBUTE_NORETURN@
+#   define _GL_ATTRIBUTE_NORETURN __attribute__ ((__noreturn__))
+#  else
+#   define _GL_ATTRIBUTE_NORETURN
+#  endif
+_GL_FUNCDECL_SYS (_Exit, void, (int status)) _GL_ATTRIBUTE_NORETURN;
 # endif
 _GL_CXXALIAS_SYS (_Exit, void, (int status));
 _GL_CXXALIASWARN (_Exit);

--- a/m4/_Exit.m4
+++ b/m4/_Exit.m4
@@ -1,4 +1,4 @@
-# _Exit.m4 serial 1
+# _Exit.m4 serial 2
 dnl Copyright (C) 2010-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -7,6 +7,8 @@
 AC_DEFUN([gl_FUNC__EXIT],
 [
   AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
+  AC_REQUIRE([gl_ATTRIBUTE_NORETURN])
+
   AC_CHECK_FUNCS([_Exit])
   if test $ac_cv_func__Exit = no; then
     HAVE__EXIT=0

new file mode 100644
--- /dev/null
+++ b/m4/attribute.m4
@@ -0,0 +1,29 @@
+# Test for GCC-style __attribute__ support.
+
+dnl Copyright (C) 2011 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.
+
+dnl from Paul Eggert
+
+# Currently only __attribute__ ((__noreturn__)) is done,
+# but other macros can be added to this file as needed.
+
+# Test whether __attribute__ ((__noreturn__)) works.
+AC_DEFUN([gl_ATTRIBUTE_NORETURN], [
+  AC_CACHE_CHECK([for  __attribute__ ((__noreturn__))],
+    [gl_cv_attribute_noreturn],
+    [gl_save_werror_flag=$ac_[]_AC_LANG_ABBREV[]_werror_flag
+     ac_[]_AC_LANG_ABBREV[]_werror_flag=yes
+     AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[void never_come_back (int) __attribute__ ((__noreturn__));]])],
+       [gl_cv_attribute_noreturn=yes],
+       [gl_cv_attribute_noreturn=no])
+     ac_[]_AC_LANG_ABBREV[]_werror_flag=$gl_save_werror_flag])
+  if test $gl_cv_attribute_noreturn = no; then
+    HAVE_ATTRIBUTE_NORETURN=0
+  fi
+  AC_SUBST([HAVE_ATTRIBUTE_NORETURN])
+])

--- a/m4/stdlib_h.m4
+++ b/m4/stdlib_h.m4
@@ -1,4 +1,4 @@
-# stdlib_h.m4 serial 36
+# stdlib_h.m4 serial 37
 dnl Copyright (C) 2007-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -65,6 +65,7 @@
   dnl Assume proper GNU behavior unless another module says otherwise.
   HAVE__EXIT=1;              AC_SUBST([HAVE__EXIT])
   HAVE_ATOLL=1;              AC_SUBST([HAVE_ATOLL])
+  HAVE_ATTRIBUTE_NORETURN=1; AC_SUBST([HAVE_ATTRIBUTE_NORETURN])
   HAVE_CANONICALIZE_FILE_NAME=1;  AC_SUBST([HAVE_CANONICALIZE_FILE_NAME])
   HAVE_DECL_GETLOADAVG=1;    AC_SUBST([HAVE_DECL_GETLOADAVG])
   HAVE_GETSUBOPT=1;          AC_SUBST([HAVE_GETSUBOPT])

--- a/modules/_Exit
+++ b/modules/_Exit
@@ -4,6 +4,7 @@
 Files:
 lib/_Exit.c
 m4/_Exit.m4
+m4/attribute.m4
 
 Depends-on:
 stdlib

--- a/modules/stdlib
+++ b/modules/stdlib
@@ -57,6 +57,7 @@
 	      < $(srcdir)/stdlib.in.h | \
 	  sed -e 's|@''HAVE__EXIT''@|$(HAVE__EXIT)|g' \
 	      -e 's|@''HAVE_ATOLL''@|$(HAVE_ATOLL)|g' \
+	      -e 's|@''HAVE_ATTRIBUTE_NORETURN''@|$(HAVE_ATTRIBUTE_NORETURN)|g' \
 	      -e 's|@''HAVE_CANONICALIZE_FILE_NAME''@|$(HAVE_CANONICALIZE_FILE_NAME)|g' \
 	      -e 's|@''HAVE_DECL_GETLOADAVG''@|$(HAVE_DECL_GETLOADAVG)|g' \
 	      -e 's|@''HAVE_GETSUBOPT''@|$(HAVE_GETSUBOPT)|g' \