[PATCH 5/5] debug: BUILD_BUG_ON: error on non-const expressions

[Boaz Harrosh <bharrosh@panasas.com>]

From: Rusty Russell <rusty@rustcorp.com.au>

Fix BUILD_BUG_ON to not silently drop non-compile-time
visible expressions.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
CC: Ingo Molnar <mingo@elte.hu>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Theodore Tso <tytso@mit.edu>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Jan Beulich <jbeulich@novell.com>
CC: David S. Miller <davem@davemloft.net>
CC: Ivo van Doorn <IvDoorn@gmail.com>
CC: John W. Linville <linville@tuxdriver.com>
---
 include/linux/compiler.h |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 90fa975..f677ab9 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -195,7 +195,10 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
 
 /* Force a compilation error if condition is true */
-#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+#define BUILD_BUG_ON(condition)					  \
+do {									  \
+	static struct { char arr[1 - 2*!!(condition)]; } x __maybe_unused;\
+} while(0)
 
 /* Force a compilation error if condition is true, but also produce a
    result (of value 0 and type size_t), so the expression can be used
-- 
1.5.6.rc1.5.gadf6