Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755955Ab2KVTHa (ORCPT ); Thu, 22 Nov 2012 14:07:30 -0500 Received: from mail.skyhub.de ([78.46.96.112]:40171 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755663Ab2KVTHZ (ORCPT ); Thu, 22 Nov 2012 14:07:25 -0500 Date: Thu, 22 Nov 2012 14:43:42 +0100 From: Borislav Petkov To: Daniel Santos Cc: LKML , Andi Kleen , Andrea Arcangeli , Andrew Morton , Christopher Li , David Daney , David Rientjes , Joe Perches , Josh Triplett , linux-sparse@vger.kernel.org, Michel Lespinasse , Paul Gortmaker , Peter Zijlstra , Steven Rostedt , Daniel Santos Subject: Re: [PATCH v6 8/9] compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,_ON} Message-ID: <20121122134342.GD17147@x1.alien8.de> Mail-Followup-To: Borislav Petkov , Daniel Santos , LKML , Andi Kleen , Andrea Arcangeli , Andrew Morton , Christopher Li , David Daney , David Rientjes , Joe Perches , Josh Triplett , linux-sparse@vger.kernel.org, Michel Lespinasse , Paul Gortmaker , Peter Zijlstra , Steven Rostedt References: <1353444132-6809-1-git-send-email-daniel.santos@pobox.com> <1353445507-7233-8-git-send-email-daniel.santos@pobox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1353445507-7233-8-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: 1922 Lines: 38 On Tue, Nov 20, 2012 at 03:05:06PM -0600, danielfsantos@att.net wrote: > 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. > > Note that we are not changing the negative-sized array code for the > unoptimized version of BUILD_BUG_ON, since it has the potential to catch > problems that would be disabled in later versions of gcc were > __compiletime_error_fallback used. The reason is that that an > unoptimized build can't always remove calls to an error-attributed > function call (like we are using) that should effectively become dead > code if it were optimized. However, using a negative-sized array with a > similar value will not result in an false-positive (error). The only > caveat being that it will also fail to catch valid conditions, which we > should be expecting in an unoptimized build anyway. > > Signed-off-by: Daniel Santos Acked-by: Borislav Petkov -- 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/