From mboxrd@z Thu Jan 1 00:00:00 1970 From: danielfsantos@att.net Subject: [PATCH v2 07/10] compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,_ON} Date: Fri, 5 Oct 2012 14:42:46 -0500 Message-ID: <1349466169-20637-7-git-send-email-daniel.santos@pobox.com> References: <1349465759-20524-1-git-send-email-daniel.santos@pobox.com> Return-path: Received: from nm5.bullet.mail.sp2.yahoo.com ([98.139.91.75]:21333 "HELO nm5.bullet.mail.sp2.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S964803Ab2JETnm (ORCPT ); Fri, 5 Oct 2012 15:43:42 -0400 In-Reply-To: <1349465759-20524-1-git-send-email-daniel.santos@pobox.com> Sender: linux-sparse-owner@vger.kernel.org List-Id: linux-sparse@vger.kernel.org To: LKML Cc: Andi Kleen , Andrea Arcangeli , Andrew Morton , Borislav Petkov , Christopher Li , David Daney , David Howells , David Rientjes , Joe Perches , Konstantin Khlebnikov , linux-sparse@vger.kernel.org, Michel Lespinasse , Paul Gortmaker , Pavel Pisa , Peter Zijlstra , Steven Rostedt , Daniel Santos Prior to the introduction of __attribute__((error("msg"))) in gcc 4.3, creating compile-time errors required a little trickery. BUILD_BUG{,_ON} uses this attribute when available to generate compile-time errors, but also uses the negative-sized array trick for older compilers, resulting in two error messages in some cases. The reason it's "some" cases is that as of gcc 4.4, the negative-sized array will not create an error in some situations, like inline functions. This patch replaces the negative-sized array code with the new __compiletime_error_fallback() macro which expands to the same thing unless the the error attribute is available, in which case it expands to (0), resulting in exactly one compile-time error on all versions of gcc. Signed-off-by: Daniel Santos --- include/linux/bug.h | 4 ++-- include/linux/compiler.h | 5 +++++ 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/include/linux/bug.h b/include/linux/bug.h index 3d4b564..f8eae31 100644 --- a/include/linux/bug.h +++ b/include/linux/bug.h @@ -56,13 +56,13 @@ struct pt_regs; * link-time error, which is harder to track down. */ #ifndef __OPTIMIZE__ -#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)])) +#define BUILD_BUG_ON(condition) __compiletime_error_fallback(condition) #else #define BUILD_BUG_ON(condition) \ do { \ extern void __build_bug_on_failed(void) \ __compiletime_error("BUILD_BUG_ON failed"); \ - ((void)sizeof(char[1 - 2*!!(condition)])); \ + __compiletime_error_fallback(condition); \ if (condition) \ __build_bug_on_failed(); \ } while(0) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index fd455aa..88ba201 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -296,6 +296,11 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); #endif #ifndef __compiletime_error # define __compiletime_error(message) +# define __compiletime_error_fallback(condition) \ + ((void)sizeof(char[1 - 2*!!(condition)])) +#endif +#ifndef __compiletime_error_fallback +# define __compiletime_error_fallback(condition) (void)(0) #endif /* * Prevent the compiler from merging or refetching accesses. The compiler -- 1.7.3.4