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From: Konstantin Khlebnikov <khlebnikov@openvz.org>
To: Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Geert Uytterhoeven <geert@linux-m68k.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Cong Wang <xiyou.wangcong@gmail.com>
Subject: [PATCH v2 1/2] bug: introduce BUILD_BUG_ON_INVALID() macro
Date: Sat, 28 Apr 2012 11:06:54 +0400	[thread overview]
Message-ID: <20120428070654.21258.25380.stgit@zurg> (raw)
In-Reply-To: <20120425112623.26927.43229.stgit@zurg>

Sometimes we want to check some expressions correctness in compile-time.
"(void)(e);" or "if (e);" can be dangerous if expression has side-effects, and
gcc sometimes generates a lot of code, even if the expression has no effect.

This patch introduces macro BUILD_BUG_ON_INVALID() for such checks,
it forces a compilation error if expression is invalid without any extra code.

[Cast to "long" required because sizeof does not work for bit-fields.]

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 include/linux/bug.h |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index 72961c3..aaac4bb 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -30,6 +30,13 @@ struct pt_regs;
 #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
 #define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
 
+/*
+ * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
+ * expression but avoids the generation of any code, even if that expression
+ * has side-effects.
+ */
+#define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
+
 /**
  * BUILD_BUG_ON - break compile if a condition is true.
  * @condition: the condition which the compiler should know is false.


WARNING: multiple messages have this Message-ID (diff)
From: Konstantin Khlebnikov <khlebnikov@openvz.org>
To: Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Geert Uytterhoeven <geert@linux-m68k.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Cong Wang <xiyou.wangcong@gmail.com>
Subject: [PATCH v2 1/2] bug: introduce BUILD_BUG_ON_INVALID() macro
Date: Sat, 28 Apr 2012 11:06:54 +0400	[thread overview]
Message-ID: <20120428070654.21258.25380.stgit@zurg> (raw)
In-Reply-To: <20120425112623.26927.43229.stgit@zurg>

Sometimes we want to check some expressions correctness in compile-time.
"(void)(e);" or "if (e);" can be dangerous if expression has side-effects, and
gcc sometimes generates a lot of code, even if the expression has no effect.

This patch introduces macro BUILD_BUG_ON_INVALID() for such checks,
it forces a compilation error if expression is invalid without any extra code.

[Cast to "long" required because sizeof does not work for bit-fields.]

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 include/linux/bug.h |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index 72961c3..aaac4bb 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -30,6 +30,13 @@ struct pt_regs;
 #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
 #define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
 
+/*
+ * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
+ * expression but avoids the generation of any code, even if that expression
+ * has side-effects.
+ */
+#define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
+
 /**
  * BUILD_BUG_ON - break compile if a condition is true.
  * @condition: the condition which the compiler should know is false.

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  parent reply	other threads:[~2012-04-28  7:07 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-25 11:26 [PATCH 1/4] compiler.h: introduce unused_expression() macro Konstantin Khlebnikov
2012-04-25 11:26 ` [PATCH 2/4] bug: completely remove code of disabled VM_BUG_ON() Konstantin Khlebnikov
2012-04-25 14:40   ` Geert Uytterhoeven
2012-04-26 22:32     ` Andrew Morton
2012-04-27  5:17       ` Geert Uytterhoeven
2012-04-27  7:07         ` Andrew Morton
2012-04-25 11:26 ` [PATCH 3/4] bug: completely remove code of disabled BUG_ON() Konstantin Khlebnikov
2012-04-25 11:26 ` [PATCH 4/4] bug: mark disabled BUG() as unreachable() code Konstantin Khlebnikov
2012-04-28  5:10   ` Konstantin Khlebnikov
2012-04-28  5:21     ` Linus Torvalds
2012-04-28  6:14     ` Andrew Morton
2012-04-25 11:51 ` [PATCH 1/4] compiler.h: introduce unused_expression() macro Cong Wang
2012-04-25 11:54   ` Konstantin Khlebnikov
2012-04-26 22:29 ` Andrew Morton
2012-04-27  9:55   ` Konstantin Khlebnikov
2012-04-27 21:53     ` Andrew Morton
2012-04-26 22:34 ` Andrew Morton
2012-04-27  7:54   ` Konstantin Khlebnikov
2012-04-27  8:16 ` H. Peter Anvin
2012-04-28  3:50   ` Konstantin Khlebnikov
2012-04-28  7:06 ` Konstantin Khlebnikov [this message]
2012-04-28  7:06   ` [PATCH v2 1/2] bug: introduce BUILD_BUG_ON_INVALID() macro Konstantin Khlebnikov
2012-04-28  7:06 ` [PATCH v2 2/2] bug: completely remove code of disabled VM_BUG_ON() Konstantin Khlebnikov
2012-04-28  7:06   ` Konstantin Khlebnikov

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