From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756927Ab2JETnm (ORCPT ); Fri, 5 Oct 2012 15:43:42 -0400 Received: from nm20-vm3.bullet.mail.ne1.yahoo.com ([98.138.91.150]:35837 "HELO nm20-vm3.bullet.mail.ne1.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S964787Ab2JETng (ORCPT ); Fri, 5 Oct 2012 15:43:36 -0400 X-Yahoo-Newman-Id: 119548.88533.bm@omp1030.access.mail.mud.yahoo.com X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: FNrbDlwVM1nIs2gUh46jTqFxTwRnxrp5IOxIR0WlVp2Cm6e CFzeEL3pd0RwARfX5myvTIWPNr1zn14vVqGw08b9jUXSAeqMdUOdq8nqS5wN n7SRyVZQIHN54rrtE.DnT6dhUOq_kHx2hRgD25M25w13zfVQ0VYUczlOf_Hl VvmQ7sXsXxb1HsqPz60GOnAruajfBWMmjGBaCeso2KxPEKabnq5emiScXavU Tu4bZ.lBEmxR.43dOBHNZFSSonZX1lhkkwnzyRosJ5qLfjE41q7V1YhipntR _oTsR2w3fu5wxYmQ0lJH8g8XY1JVTVLq9UYgx9je2ttJP0ftxnbOakBaEKN3 WUPbET2g.Rdbe5YeDFw9_9VOs6aiJgW1rl46Y0HWjDnvnCkGospBxT_Jbpbf mz9CWOlNgTk3EvDDb0Bxh7bQhkJE1kgCydof7gvGB94ZMJJFIZXkO X-Yahoo-SMTP: xXkkXk6swBBAi.5wfkIWFW3ugxbrqyhyk_b4Z25Sfu.XGQ-- From: danielfsantos@att.net 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 Subject: [PATCH v2 06/10] bug.h: Make BUILD_BUG_ON generate compile-time error Date: Fri, 5 Oct 2012 14:42:45 -0500 Message-Id: <1349466169-20637-6-git-send-email-daniel.santos@pobox.com> X-Mailer: git-send-email 1.7.3.4 In-Reply-To: <1349465759-20524-1-git-send-email-daniel.santos@pobox.com> References: <1349465759-20524-1-git-send-email-daniel.santos@pobox.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Negative sized arrays wont create a compile-time error in some cases starting with gcc 4.4 (e.g., inlined functions), but gcc 4.3 introduced the error function attribute that will. This patch modifies BUILD_BUG_ON to behave like BUILD_BUG already does, using the error function attribute so that you don't have to build the entire kernel to discover that you have a problem, and then enjoy trying to track it down from a link-time error. Signed-off-by: Daniel Santos --- include/linux/bug.h | 24 ++++++++++++++---------- 1 files changed, 14 insertions(+), 10 deletions(-) diff --git a/include/linux/bug.h b/include/linux/bug.h index a03c3ef..3d4b564 100644 --- a/include/linux/bug.h +++ b/include/linux/bug.h @@ -43,24 +43,28 @@ struct pt_regs; * @condition: the condition which the compiler should know is false. * * If you have some code which relies on certain constants being equal, or - * other compile-time-evaluated condition, you should use BUILD_BUG_ON to + * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to * detect if someone changes it. * * The implementation uses gcc's reluctance to create a negative array, but * gcc (as of 4.4) only emits that error for obvious cases (eg. not arguments - * to inline functions). So as a fallback we use the optimizer; if it can't - * prove the condition is false, it will cause a link error on the undefined - * "__build_bug_on_failed". This error message can be harder to track down - * though, hence the two different methods. + * to inline functions). Luckily, in 4.3 they added the "error" function + * attribute just for this type of case. Thus, we use a negative sized array + * (should always create an error pre-gcc-4.4) and then call an undefined + * function with the error attribute (should always creates an error 4.3+). If + * for some reason, neither creates a compile-time error, we'll still have a + * link-time error, which is harder to track down. */ #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"); \ + ((void)sizeof(char[1 - 2*!!(condition)])); \ + if (condition) \ + __build_bug_on_failed(); \ } while(0) #endif -- 1.7.3.4