linux-kernel - [PATCH] utilize _Static_assert() for BUILD_BUG

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Date:	Fri, 02 Nov 2012 14:47:40 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<akpm@...ux-foundation.org>, <rusty@...tcorp.com.au>
Cc:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] utilize _Static_assert() for BUILD_BUG_ON() when the
 compiler supports it

This makes the resulting diagnostics quite a bit more useful.

Signed-off-by: Jan Beulich <jbeulich@...e.com>

---
 include/linux/bug.h |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- 3.7-rc3/include/linux/bug.h
+++ 3.7-rc3-static-assert/include/linux/bug.h
@@ -27,8 +27,15 @@ struct pt_regs;
    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
    aren't permitted). */
+#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
+#define BUILD_BUG_ON_ZERO(e) \
+	sizeof(struct { _Static_assert(!(e), "!(" #e ")"); })
+#define BUILD_BUG_ON_NULL(e) \
+	((void *)sizeof(struct { _Static_assert(!(e), "!(" #e ")"); }))
+#else
 #define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
 #define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
+#endif
 
 /*
  * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the
@@ -54,6 +61,15 @@ struct pt_regs;
  */
 #ifndef __OPTIMIZE__
 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+#elif __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)
+#define __build_bug_on_failed(n) __build_bug_on_##n##_failed
+#define _BUILD_BUG_ON(n, condition)				\
+	do {							\
+		extern void __compiletime_error(#condition)	\
+		__build_bug_on_failed(n)(void);			\
+		if (condition) __build_bug_on_failed(n)();	\
+	} while(0)
+#define BUILD_BUG_ON(condition...) _BUILD_BUG_ON(__COUNTER__, ##condition)
 #else
 extern int __build_bug_on_failed;
 #define BUILD_BUG_ON(condition)					\



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