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SubjectRe: [PATCH 5/5 ver3] debug: BUILD_BUG_ON: error on non-const expressions

Fix BUILD_BUG_ON to not silently drop non-compile-time
visible expressions. It will now produce a compilation
error if so.

The code to BUILD_BUG_ON_ZERO was done by:
Jan Beulich <jbeulich@novell.com>

The code to BUILD_BUG_ON is a small variation to Jan's
code inspired by Rusty Russell. Which gives me better
compilations semantics, and makes BUILD_BUG_ON behave
more like BUG_ON.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
TO: Jan Beulich <jbeulich@novell.com>
CC: Ingo Molnar <mingo@elte.hu>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Theodore Tso <tytso@mit.edu>
CC: David S. Miller <davem@davemloft.net>
---
include/linux/compiler.h | 11 ++++++-----
1 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 90fa975..f882410 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -194,14 +194,15 @@ 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)]))
-
/* 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
- e.g. in a structure initializer (or where-ever else comma expressions
+ e.g. in a structure initializer (or where-ever full statements
aren't permitted). */
-#define BUILD_BUG_ON_ZERO(e) (sizeof(char[1 - 2 * !!(e)]) - 1)
+#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int: -!!(e); }))
+
+/* Force a compilation error if condition is true */
+#define BUILD_BUG_ON(e) \
+ do { struct {int: -!!(e); } x __maybe_unused; } while (0)

/* Trap pasters of __FUNCTION__ at compile-time */
#define __FUNCTION__ (__func__)
--
1.5.6.rc1.5.gadf6



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