From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932924Ab2JXQmO (ORCPT ); Wed, 24 Oct 2012 12:42:14 -0400 Received: from nm27.access.bullet.mail.sp2.yahoo.com ([98.139.44.154]:46381 "EHLO nm27.access.bullet.mail.sp2.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935194Ab2JXQj6 (ORCPT ); Wed, 24 Oct 2012 12:39:58 -0400 X-Yahoo-Newman-Id: 265290.79197.bm@smtp105.sbc.mail.gq1.yahoo.com X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: oycLA7oVM1nmvGXeQz1DLxc9bbV2Xqy00DT2_14TKFUBHXA QhQsqzTE2G1HwCu.O0gF5ZpMYtGhq7u_8yC0Pu4ARaLpqWtpkna5u2EDljrn 0NP9MNAUOCBkp8RcHeCOzHa4Z0eKLbRtwe6sQ6Dfiwx5HfWMURbJbPoDbq7t rfcKoqPOoGhcN9.xUHwwNCg5RFthauOOaDla1TToaZ3bN5wUH4fWwLbNVDPf T4zvxKQsTl8eqEn558pyv2M4iX6a_VKerQOFxs7WcTlb2COHQwnnHH6TP6Cq OWojmnfEhNHE9V1dMr1ELDtDLqr.tbGyErp0wGF5ArUc3I98C9hmisb_Y7Lq AzHX8Km9piquDQPK9U9v6Q8VRtAKHYcA7XBCyDBxjK1rfUM0i0Cog4Df4XZA URzTfx1gJI_UGL752d2G40HdBq319Ayx3lx9qftCXlCwaErq9rrjq X-Yahoo-SMTP: xXkkXk6swBBAi.5wfkIWFW3ugxbrqyhyk_b4Z25Sfu.XGQ-- From: danielfsantos@att.net To: LKML , Andi Kleen , Andrea Arcangeli , Andrew Morton , Christopher Li , Daniel Santos , David Daney , David Howells , Joe Perches , Josh Triplett , Konstantin Khlebnikov , linux-sparse@vger.kernel.org, Michel Lespinasse , Paul Gortmaker , Pavel Pisa , Peter Zijlstra , Steven Rostedt , Borislav Petkov , David Rientjes Subject: [PATCH v3 06/10] bug.h: Make BUILD_BUG_ON generate compile-time error Date: Wed, 24 Oct 2012 11:33:57 -0500 Message-Id: <1351096441-12388-6-git-send-email-daniel.santos@pobox.com> X-Mailer: git-send-email 1.7.3.4 In-Reply-To: <1351096132-12244-1-git-send-email-daniel.santos@pobox.com> References: <1351096132-12244-1-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