Commit baf05aa9 authored May 29, 2012 by Konstantin Khlebnikov Committed by Linus Torvalds May 29, 2012

bug: introduce BUILD_BUG_ON_INVALID() macro



Sometimes we want to check some expressions correctness at compile time.
"(void)(e);" or "if (e);" can be dangerous if the 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>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5febcbe9

include/linux/bug.h

+7 −0

Original line number	Diff line number	Diff line
		@@ -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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