Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755826Ab2J1U5S (ORCPT ); Sun, 28 Oct 2012 16:57:18 -0400 Received: from nm27.access.bullet.mail.mud.yahoo.com ([66.94.237.92]:23792 "EHLO nm27.access.bullet.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755722Ab2J1U5P (ORCPT ); Sun, 28 Oct 2012 16:57:15 -0400 X-Yahoo-Newman-Id: 304948.16106.bm@smtp105.sbc.mail.ne1.yahoo.com X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: 8q1j.wsVM1m9YwThdbvPshnYq0RSY6Izj1dtkx6ZGQ4xzEV q0FUwRfVrKSo.atDtrIIlmoylYC7VZ83P7t_XtgI8xgfXqXmwxiYHnBMOiQz Z4B44cDKRnU5lVKLP3y1y6NsMAuWKCewCcX6cEgBZlcZOVq3QLvpGnM5JazG uJBTJxNrqSI1izf9lCDrdy2.2.tUO1EY66lpNcR_YUaQdslps3K7xJp44c7Y 9gkl.WgfCDLqZ_s57RTmHR2SlguVsnzdMdGqHYs.PjmKblQ019r2dJotjIOF hVUFV8eG5N9IGpnImxOQfcjmqxKutFEbq2.ATG9Ihk3AG2BF5NzlffYbdC65 Hl15Z8ALPWmmJ5oWAQmpoTNjE2RTzcY3Xh615bsBXyzVRBD44MTyf6Qf_PGD aeS4BNM123adI4ZJYPiEl79UVmG37poPy9G9bHK0mTt3mVIHzn8NNtfGICLl BqYtK3WyeFyQUxdi2aQqQT6SvIpcA 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 v4 6/9] compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,_ON} Date: Sun, 28 Oct 2012 15:57:12 -0500 Message-Id: <1351457835-7553-6-git-send-email-daniel.santos@pobox.com> X-Mailer: git-send-email 1.7.3.4 In-Reply-To: <1351457648-7453-1-git-send-email-daniel.santos@pobox.com> References: <1351457648-7453-1-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: 2561 Lines: 66 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 do{}while(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 | 7 +++++++ 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/include/linux/bug.h b/include/linux/bug.h index 03259d7..da03dc1 100644 --- a/include/linux/bug.h +++ b/include/linux/bug.h @@ -57,13 +57,13 @@ struct pt_regs; * 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 cbf6d9d..84926f2 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -298,6 +298,13 @@ 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) \ + do { \ + ((void)sizeof(char[1 - 2*!!(condition)])); \ + } while (0) +#endif +#ifndef __compiletime_error_fallback +# define __compiletime_error_fallback(condition) do { } while (0) #endif /* * Prevent the compiler from merging or refetching accesses. The compiler -- 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/