# HG changeset patch
# User Paul Eggert <eggert@cs.ucla.edu>
# Date 1364611633 25200
# Node ID 7524d97ae56f27b929fb8ea005242fc33b6f0e5e
# Parent  5a51fb7777a9950502965a043a70bd6ca5e0498b
stdalign: port to stricter ISO C11

ISO C11 says that _Alignof's operand must be a parenthesized type.
Problem reported by Eli Zaretskii in
<http://lists.gnu.org/archive/html/emacs-devel/2013-03/msg00960.html>.
* doc/posix-headers/stdalign.texi (stdalign.h): Document this.
* m4/stdalign.m4 (gl_STDALIGN_H): Don't use _Alignof (expr).

diff -r 5a51fb7777a9 -r 7524d97ae56f ChangeLog
--- a/ChangeLog	Tue Mar 19 09:08:47 2013 -0700
+++ b/ChangeLog	Fri Mar 29 19:47:13 2013 -0700
@@ -1,3 +1,12 @@
+2013-03-29  Paul Eggert  <eggert@cs.ucla.edu>
+
+	stdalign: port to stricter ISO C11
+	ISO C11 says that _Alignof's operand must be a parenthesized type.
+	Problem reported by Eli Zaretskii in
+	<http://lists.gnu.org/archive/html/emacs-devel/2013-03/msg00960.html>.
+	* doc/posix-headers/stdalign.texi (stdalign.h): Document this.
+	* m4/stdalign.m4 (gl_STDALIGN_H): Don't use _Alignof (expr).
+
 2013-03-21  Paul Eggert  <eggert@cs.ucla.edu>
 
 	sys_select, sys_time: port 2013-01-30 Solaris 2.6 fix to Cygwin
diff -r 5a51fb7777a9 -r 7524d97ae56f doc/posix-headers/stdalign.texi
--- a/doc/posix-headers/stdalign.texi	Tue Mar 19 09:08:47 2013 -0700
+++ b/doc/posix-headers/stdalign.texi	Fri Mar 29 19:47:13 2013 -0700
@@ -25,6 +25,13 @@
 Portability problems not fixed by Gnulib:
 @itemize
 @item
+In ISO C11, the operand of @code{alignof}/@code{_Alignof} must be a
+parenthesized type.  Recent versions of GCC support an extension in
+which the operand can also be a unary expression, as with
+@code{sizeof}.  We don't know of any compilers that support
+@code{alignof}/@code{_Alignof} without also supporting this extension;
+if you find one please let us know.
+@item
 @code{_Alignas} and @code{alignas} are not always supported;
 on platforms lacking support, the
 macro @code{__alignas_is_defined} is not defined.
diff -r 5a51fb7777a9 -r 7524d97ae56f m4/stdalign.m4
--- a/m4/stdalign.m4	Tue Mar 19 09:08:47 2013 -0700
+++ b/m4/stdalign.m4	Fri Mar 29 19:47:13 2013 -0700
@@ -33,8 +33,9 @@
             #if \
                 (__GNUC__ || __IBMC__ || __IBMCPP__ \
                  || 0x5110 <= __SUNPRO_C || 1300 <= _MSC_VER)
-              int alignas (8) alignas_int = 1;
-              char test_alignas[_Alignof (alignas_int) == 8 ? 1 : -1];
+              struct alignas_test { char c; char alignas (8) alignas_8; };
+              char test_alignas[offsetof (struct alignas_test, alignas_8) == 8
+                                ? 1 : -1];
             #endif
           ]])],
        [gl_cv_header_working_stdalign_h=yes],