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List: gnulib-bug
Subject: [PATCH] stdalign: port to stricter ISO C11
From: Paul Eggert <eggert () cs ! ucla ! edu>
Date: 2013-03-30 2:48:45
Message-ID: 5156528D.4070608 () cs ! ucla ! edu
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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).
---
ChangeLog | 9 +++++++++
doc/posix-headers/stdalign.texi | 7 +++++++
m4/stdalign.m4 | 5 +++--
3 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 3843c33..768f3a7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -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 --git a/doc/posix-headers/stdalign.texi b/doc/posix-headers/stdalign.texi
index 8e34673..cad83f6 100644
--- a/doc/posix-headers/stdalign.texi
+++ b/doc/posix-headers/stdalign.texi
@@ -25,6 +25,13 @@ the types @code{double} and @code{long long} in GCC 4.7.0.
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 --git a/m4/stdalign.m4 b/m4/stdalign.m4
index 3d7993d..a866ff6 100644
--- a/m4/stdalign.m4
+++ b/m4/stdalign.m4
@@ -33,8 +33,9 @@ AC_DEFUN([gl_STDALIGN_H],
#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],
--
1.7.11.7
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