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authorKonstantin Khlebnikov <khlebnikov@openvz.org>2012-05-29 15:06:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-29 16:22:20 -0700
commitbaf05aa9271bdbc07d3160035a231abc5fbd429a (patch)
tree201c4f1df332fa2baef4ddfeda6806faf9e2dbc8 /include/linux/bug.h
parent5febcbe99d4766cc383909c447e002e63d8b4592 (diff)
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>
Diffstat (limited to 'include/linux/bug.h')
-rw-r--r--include/linux/bug.h7
1 files changed, 7 insertions, 0 deletions
diff --git a/include/linux/bug.h b/include/linux/bug.h
index 72961c39576a..aaac4bba6f5c 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.