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Re: test-stdalign.c breaks on i686 on Fedora Rawhide (gcc 4.7)
From: |
Paul Eggert |
Subject: |
Re: test-stdalign.c breaks on i686 on Fedora Rawhide (gcc 4.7) |
Date: |
Fri, 27 Jan 2012 10:23:49 -0800 |
User-agent: |
Mozilla/5.0 (X11; Linux i686; rv:9.0) Gecko/20111229 Thunderbird/9.0 |
Thanks for reporting this. I expect this is a GCC 4.7 bug, and
have filed a bug report. I pushed the following workaround
into Gnulib. If I'm wrong and it's not a GCC bug then we can
revisit this.
stdalign: check that alignof and offsetof are consistent
* m4/stdalign.m4 (gl_STDALIGN_H): Check for GCC bug 52023.
Problem reported for gnulib by Richard W.M. Jones in
<http://lists.gnu.org/archive/html/bug-gnulib/2012-01/msg00340.html>.
diff --git a/m4/stdalign.m4 b/m4/stdalign.m4
index 9752ba5..fa6d5d5 100644
--- a/m4/stdalign.m4
+++ b/m4/stdalign.m4
@@ -14,13 +14,26 @@ AC_DEFUN([gl_STDALIGN_H],
[AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM(
[[#include <stdalign.h>
- int align_int = alignof (int) + _Alignof (double);
+ #include <stddef.h>
+
+ /* Test that alignof yields a result consistent with offsetof.
+ This catches GCC bug 52023
+ <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>. */
+ #ifdef __cplusplus
+ template <class t> struct alignof_helper { char a; t b; };
+ # define ao(type) offsetof (alignof_helper<type>, b)
+ #else
+ # define ao(type) offsetof (struct { char a; type b; }, b)
+ #endif
+ char test1[_Alignof (double) == ao (double) ? 1 : -1];
+ char test2[alignof (long int) == ao (long int) ? 1 : -1];
/* Test _Alignas only on platforms where gnulib can help. */
#if \
(__GNUC__ || __IBMC__ || __IBMCPP__ \
|| 0x5110 <= __SUNPRO_C || 1300 <= _MSC_VER)
int alignas (8) alignas_int = 1;
+ char test3[8 <= _Alignof (alignas_int) ? 1 : -1];
#endif
]])],
[gl_cv_header_working_stdalign_h=yes],