linux-kernel - [PATCH v7 6/9] bug.h: Prevent double evaulation of in BUILD_BUG

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Date:	Tue,  1 Jan 2013 15:09:54 -0600
From:	danielfsantos@....net
To:	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Rientjes <rientjes@...gle.com>,
	Joe Perches <joe@...ches.com>,
	Josh Triplett <josh@...htriplett.org>,
	linux-sparse@...r.kernel.org,
	Michel Lespinasse <walken@...gle.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	Daniel Santos <daniel.santos@...ox.com>
Subject: [PATCH v7 6/9] bug.h: Prevent double evaulation of 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.

Signed-off-by: Daniel Santos <daniel.santos@...ox.com>
---
 include/linux/bug.h |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index 27d404f..0d75762 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -59,8 +59,9 @@ 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;	\
+		bool __cond = !!(condition);			\
+		((void)sizeof(char[1 - 2 * __cond]));		\
+		if (__cond) __build_bug_on_failed = 1;		\
 	} while(0)
 #endif
 
-- 
1.7.8.6

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