From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751631Ab2JAA07 (ORCPT ); Sun, 30 Sep 2012 20:26:59 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:37671 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751132Ab2JAA05 convert rfc822-to-8bit (ORCPT ); Sun, 30 Sep 2012 20:26:57 -0400 X-Originating-IP: 217.70.178.131 X-Originating-IP: 50.43.46.74 Date: Sun, 30 Sep 2012 17:26:49 -0700 From: Josh Triplett To: Daniel Santos Cc: LKML , Andi Kleen , Andrea Arcangeli , Andrew Morton , Christopher Li , David Daney , David Howells , Joe Perches , Konstantin Khlebnikov , linux-sparse@vger.kernel.org, Michel Lespinasse , Paul Gortmaker , Pavel Pisa , Peter Zijlstra , Steven Rostedt Subject: Re: [PATCH 8/10] bug.h: Make BUILD_BUG_ON generate compile-time error Message-ID: <20121001002649.GB16784@leaf> References: <1348874411-28288-1-git-send-email-daniel.santos@pobox.com> <1348874411-28288-9-git-send-email-daniel.santos@pobox.com> <20120929003239.GA14293@jtriplet-mobl1> <50664E30.7050809@att.net> <20120929025506.GA3183@leaf> <5068D5BD.1000802@att.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <5068D5BD.1000802@att.net> User-Agent: Mutt/1.5.21 (2010-09-15) Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 30, 2012 at 06:29:01PM -0500, Daniel Santos wrote: > On 09/28/2012 09:55 PM, Josh Triplett wrote: > > Assuming you don't call BUILD_BUG_ON_MSG more than once per line: > > > > /tmp$ cat test.c > > #define BUILD_BUG_ON_MSG_INTERNAL2(cond, msg, line) \ > > do { \ > > extern void __build_bug_on_failed_ ## line (void) __attribute__((error(msg))); \ > > if (cond) \ > > __build_bug_on_failed_ ## line(); \ > > } while (0) > > > > #define BUILD_BUG_ON_MSG_INTERNAL(cond, msg, line) BUILD_BUG_ON_MSG_INTERNAL2(cond, msg, line) > > #define BUILD_BUG_ON_MSG(cond, msg) BUILD_BUG_ON_MSG_INTERNAL(cond, msg, __LINE__) > > > > void f(void) > > { > > BUILD_BUG_ON_MSG(0, "test 1"); > > BUILD_BUG_ON_MSG(1, "test 2"); > > BUILD_BUG_ON_MSG(0, "test 3"); > > BUILD_BUG_ON_MSG(1, "test 4"); > > } > > /tmp$ gcc -c test.c > > test.c: In function ‘f’: > > test.c:14:119: error: call to ‘__build_bug_on_failed_14’ declared with attribute error: test 2 > > test.c:16:119: error: call to ‘__build_bug_on_failed_16’ declared with attribute error: test 4 > Thanks! This is very nice! I've done a little more research and > discovered that there's also a __COUNTER__ macro that is available > in gcc 4.3+. Before I realized that it was only available in gcc > 4.3, I wrote this little macro: > > #define _CONCAT1(a, b) a##b > #define CONCAT(a, b) _CONCAT1(a, b) > > #ifdef __COUNTER__ > # define UNIQUIFY(prefix) CONCAT(prefix, __COUNTER__) > #else > # define UNIQUIFY(prefix) CONCAT(prefix, __LINE__) > #endif > > However, this could lead to code might compile on gcc 4.3+, but > not compile prior, so this is bad, right? Yes, as long as Linux continues to support prior GCC versions (currently anything 3.2 or newer), I'd suggest sticking with __LINE__ so that it consistently breaks if you use more than one BUILD_BUG_ON_MSG per line. Good to know that __COUNTER__ exists, though. Also, the name BUILD_BUG_ON_MSG seems wrong to me somehow; I keep parsing it as though something about the message causes the build bug. - Josh Triplett