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Subject[PATCH 4.4 089/100] compiler.h: fix error in BUILD_BUG_ON() reporting
Date
From: Vegard Nossum <vegard.nossum@oracle.com>

[ Upstream commit af9c5d2e3b355854ff0e4acfbfbfadcd5198a349 ]

compiletime_assert() uses __LINE__ to create a unique function name. This
means that if you have more than one BUILD_BUG_ON() in the same source
line (which can happen if they appear e.g. in a macro), then the error
message from the compiler might output the wrong condition.

For this source file:

#include <linux/build_bug.h>

#define macro() \
BUILD_BUG_ON(1); \
BUILD_BUG_ON(0);

void foo()
{
macro();
}

gcc would output:

./include/linux/compiler.h:350:38: error: call to `__compiletime_assert_9' declared with attribute error: BUILD_BUG_ON failed: 0
_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)

However, it was not the BUILD_BUG_ON(0) that failed, so it should say 1
instead of 0. With this patch, we use __COUNTER__ instead of __LINE__, so
each BUILD_BUG_ON() gets a different function name and the correct
condition is printed:

./include/linux/compiler.h:350:38: error: call to `__compiletime_assert_0' declared with attribute error: BUILD_BUG_ON failed: 1
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Daniel Santos <daniel.santos@pobox.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Joe Perches <joe@perches.com>
Link: http://lkml.kernel.org/r/20200331112637.25047-1-vegard.nossum@oracle.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/compiler.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 5508011cc0c79..5f8749440c6af 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -502,7 +502,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
* compiler has support to do so.
*/
#define compiletime_assert(condition, msg) \
- _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
+ _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)

#define compiletime_assert_atomic_type(t) \
compiletime_assert(__native_word(t), \
--
2.20.1


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