[PATCH] linux/bug.h: make BUILD_BUG_ON generate compile-time error

[Daniel Santos <danielfsantos@att.net>]

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This is pretty straight-forward. __compiletime_error is defined in
compiler-gcc4.h with appropriate version checks, so shouldn't break on
older compilers. This makes the difference between getting an error at
link-time and getting one at compile time. Example:

/home/daniel/proj/kernel/grbtest/grbtest2.c:83:2: error: call to
‘__build_bug_on_failed’ declared with attribute error: BUILD_BUG_ON
failed: !__builtin_constant_p(count)

The above points me directly to where I called BUILD_BUG_ON. Note that
I'm moving __build_bug_on_failed out of the global scope, just so it can
be re-declared with different attributes each time.

Daniel

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>From 3af9a38225e6d074ef6b22e6c99c2503bc581953 Mon Sep 17 00:00:00 2001
From: Daniel Santos <daniel.santos@pobox.com>
Date: Mon, 4 Jun 2012 06:13:41 -0500
Subject: linux/bug.h: make BUILD_BUG_ON generate compile-time error

---
 include/linux/bug.h |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/bug.h b/include/linux/bug.h
index 72961c3..d35d6e9 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -48,11 +48,12 @@ struct pt_regs;
 #ifndef __OPTIMIZE__
 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
 #else
-extern int __build_bug_on_failed;
-#define BUILD_BUG_ON(condition)					\
-	do {							\
-		((void)sizeof(char[1 - 2*!!(condition)]));	\
-		if (condition) __build_bug_on_failed = 1;	\
+#define BUILD_BUG_ON(condition)						\
+	do {								\
+		extern void __build_bug_on_failed(void)			\
+		__compiletime_error("BUILD_BUG_ON failed: " #condition);\
+		((void)sizeof(char[1 - 2*!!(condition)]));		\
+		if (condition) __build_bug_on_failed();			\
 	} while(0)
 #endif
 
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1.7.3.4