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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

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

Signed-off-by: Konstantin Khlebnikov <>
Cc: Linus Torvalds <>
Cc: Geert Uytterhoeven <>
Cc: "H. Peter Anvin" <>
Cc: Cong Wang <>
Cc: Hugh Dickins <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
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koct9i authored and torvalds committed May 29, 2012
1 parent 5febcbe commit baf05aa
Showing 1 changed file with 7 additions and 0 deletions.
@@ -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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