Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935360Ab2JYJdo (ORCPT ); Thu, 25 Oct 2012 05:33:44 -0400 Received: from mail.skyhub.de ([78.46.96.112]:37510 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935099Ab2JYJdi (ORCPT ); Thu, 25 Oct 2012 05:33:38 -0400 Date: Thu, 25 Oct 2012 11:33:36 +0200 From: Borislav Petkov To: danielfsantos@att.net Cc: 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 , David Rientjes Subject: Re: [PATCH v3 06/10] bug.h: Make BUILD_BUG_ON generate compile-time error Message-ID: <20121025093336.GC16601@liondog.tnic> Mail-Followup-To: Borislav Petkov , danielfsantos@att.net, 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 , David Rientjes References: <1351096132-12244-1-git-send-email-daniel.santos@pobox.com> <1351096441-12388-6-git-send-email-daniel.santos@pobox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1351096441-12388-6-git-send-email-daniel.santos@pobox.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3224 Lines: 77 On Wed, Oct 24, 2012 at 11:33:57AM -0500, danielfsantos@att.net wrote: > 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 .... always create an error on gcc versions older than 4.4) > + * function with the error attribute (should always creates an error 4.3+). If ..... always create an error on gcc 4.3 and later) > + * 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 With the changes above: Acked-by: Borislav Petkov Thanks. -- Regards/Gruss, Boris. -- 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/