Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753670Ab2KTVIS (ORCPT ); Tue, 20 Nov 2012 16:08:18 -0500 Received: from nm12.access.bullet.mail.mud.yahoo.com ([66.94.237.213]:21807 "EHLO nm12.access.bullet.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753496Ab2KTVIN (ORCPT ); Tue, 20 Nov 2012 16:08:13 -0500 X-Yahoo-Newman-Id: 32795.4524.bm@smtp108.sbc.mail.bf1.yahoo.com X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: 11hDZkYVM1lDHOA_mLWgx015OQBbPYYFLyrf5N8GnDe9W.6 hAZLybva43YYmMIUkBT99dZqpSHwpz_uax.hHmcc.SqXTTr_yrqK1iBdhp7n 1yTxGgbT20j2CFaAPOcdUm0cwmyC81xQUKqFgXvX2N8tu7dGo90SrSyMoj3o JLAwnVZq93VpcACnWMrffaGA0H17lHhTepKjwrHYYdcF40v6WexbseRvSfxd AvjlOTb_NeJOC7NgkCqh5uvojUwbsa.iDLWHMcaneKoiKuUt9xhEGXR1gTfL zRBqr2t3t_XvX8BBB7A3yz7oU4FkM6_gkuHSDIkbXkkg2rBCmfiiBZTtr.G3 m7ho9lBBT81e9hRAoByJJDr4xYzrjMOv_h6RY3mTUGY.4XkOUGvINmCGB8tq gdwklIG_PIBfGGr7RoJDh6r6RF79v53Bv3L1jb0ZwVp08h3qADYYj_w-- X-Yahoo-SMTP: xXkkXk6swBBAi.5wfkIWFW3ugxbrqyhyk_b4Z25Sfu.XGQ-- From: danielfsantos@att.net To: LKML , Andi Kleen , Andrea Arcangeli , Andrew Morton , Borislav Petkov , Christopher Li , David Daney , David Rientjes , Joe Perches , Josh Triplett , linux-sparse@vger.kernel.org, Michel Lespinasse , Paul Gortmaker , Peter Zijlstra , Steven Rostedt Cc: Daniel Santos Subject: [PATCH v6 7/9] bug.h: Make BUILD_BUG_ON generate compile-time error Date: Tue, 20 Nov 2012 15:05:05 -0600 Message-Id: <1353445507-7233-7-git-send-email-daniel.santos@pobox.com> X-Mailer: git-send-email 1.7.3.4 In-Reply-To: <1353444132-6809-1-git-send-email-daniel.santos@pobox.com> References: <1353444132-6809-1-git-send-email-daniel.santos@pobox.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3614 Lines: 84 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. Also, we are only including asm/bug.h and then expecting that linux/compiler.h will eventually be included to define __linktime_error (used in BUILD_BUG_ON). This patch includes it directly for clarity and to avoid the possibility of changes in /*/include/asm/bug.h being changed or not including linux/compiler.h for some reason. Signed-off-by: Daniel Santos Acked-by: Borislav Petkov --- include/linux/bug.h | 32 +++++++++++++++++++------------- 1 files changed, 19 insertions(+), 13 deletions(-) diff --git a/include/linux/bug.h b/include/linux/bug.h index 98bdbb3d..eb6d715 100644 --- a/include/linux/bug.h +++ b/include/linux/bug.h @@ -2,6 +2,7 @@ #define _LINUX_BUG_H #include +#include enum bug_trap_type { BUG_TRAP_TYPE_NONE = 0, @@ -42,25 +43,30 @@ 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. + * The implementation uses gcc's reluctance to create a negative array, but gcc + * (as of 4.4) only emits that error for obvious cases (e.g. not arguments 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 on gcc versions older than 4.4) and then call + * an undefined function with the error attribute (should always create an + * error on gcc 4.3 and later). 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 { \ - bool __cond = !!(condition); \ - ((void)sizeof(char[1 - 2 * __cond])); \ - if (__cond) __build_bug_on_failed = 1; \ +#define BUILD_BUG_ON(condition) \ + do { \ + bool __cond = !!(condition); \ + extern void __build_bug_on_failed(void) \ + __compiletime_error("BUILD_BUG_ON failed"); \ + if (__cond) \ + __build_bug_on_failed(); \ + ((void)sizeof(char[1 - 2 * __cond])); \ } while(0) #endif -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/