bug.h: prevent double evaulation of `condition' in BUILD_BUG_ON

When calling BUILD_BUG_ON in an optimized build using gcc 4.3 and later,
the condition will be evaulated twice, possibily with side-effects.  This
patch eliminates that error.

[akpm@linux-foundation.org: tweak code layout]
Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Joe Perches <joe@perches.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/include/linux/bug.h b/include/linux/bug.h
index 27d404f91b3e..89fb91d0c929 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -59,9 +59,10 @@ struct pt_regs;
 extern int __build_bug_on_failed;
 #define BUILD_BUG_ON(condition)                                 \
         do {                                                    \
-                ((void)sizeof(char[1 - 2*!!(condition)]));      \
-                if (condition) __build_bug_on_failed = 1;       \
-        } while(0)
+                bool __cond = !!(condition);                    \
+                ((void)sizeof(char[1 - 2 * __cond]));           \
+                if (__cond) __build_bug_on_failed = 1;          \
+        } while (0)
 #endif
 
 /**