[PATCH] Make BUILD_BUG_ON fail at compile time.

Force a compiler error instead of a link error, because they are easier to
track down.  Idea stolen from code by Jan Beulich <jbeulich@novell.com>

If the argument to BUILD_BUG_ON evaluates to non-zero the compiler will do:

	t.c:6: error: size of array `type name' is negative

(surprised that gcc doesn't have an extension for this)

Signed-off-by: "Andi Kleen" <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 687ba8c9973de2d30d97e234817a52e6b2d2f993..4367ce4db52a1a427ba3cdc73d6100371c9f67e4 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -307,8 +307,8 @@ struct sysinfo {
        char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding: libc5 uses this.. */
 };
 
-extern void BUILD_BUG(void);
-#define BUILD_BUG_ON(condition) do { if (condition) BUILD_BUG(); } while(0)
+/* Force a compilation error if condition is false */
+#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
 
 #ifdef CONFIG_SYSCTL
 extern int randomize_va_space;