linux-kernel - [PATCH AUTOSEL 4.9 13/21] compiler.h: fix error in BUILD_BUG

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Message-Id: <20200415114748.15713-13-sashal@kernel.org>
Date:   Wed, 15 Apr 2020 07:47:40 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Vegard Nossum <vegard.nossum@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Daniel Santos <daniel.santos@...ox.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Ian Abbott <abbotti@....co.uk>, Joe Perches <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>, linux-sparse@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 13/21] compiler.h: fix error in BUILD_BUG_ON() reporting

From: Vegard Nossum <vegard.nossum@...cle.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@...cle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Reviewed-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Reviewed-by: Daniel Santos <daniel.santos@...ox.com>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Ian Abbott <abbotti@....co.uk>
Cc: Joe Perches <joe@...ches.com>
Link: http://lkml.kernel.org/r/20200331112637.25047-1-vegard.nossum@oracle.com
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.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 0020ee1cab37a..7837afabbd78e 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -546,7 +546,7 @@ unsigned long read_word_at_a_time(const void *addr)
  * 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