From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754801Ab3JQKyg (ORCPT ); Thu, 17 Oct 2013 06:54:36 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:39583 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754219Ab3JQKyf (ORCPT ); Thu, 17 Oct 2013 06:54:35 -0400 Message-ID: <525FC1DD.4030205@canonical.com> Date: Thu, 17 Oct 2013 12:54:21 +0200 From: Maarten Lankhorst User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: Peter Zijlstra , Tetsuo Handa CC: mingo@kernel.org, imirkin@alum.mit.edu, linux-kernel@vger.kernel.org, daniel.vetter@ffwll.ch, robdclark@gmail.com Subject: Re: [PATCH for 3.12] mutex: Avoid gcc version dependent __builtin_constant_p() usage. References: <201310171945.AGB17114.FSQVtHOJFOOFML@I-love.SAKURA.ne.jp> <20131017105243.GM2675@laptop.programming.kicks-ass.net> In-Reply-To: <20131017105243.GM2675@laptop.programming.kicks-ass.net> X-Enigmail-Version: 1.5.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org op 17-10-13 12:52, Peter Zijlstra schreef: > On Thu, Oct 17, 2013 at 07:45:29PM +0900, Tetsuo Handa wrote: >> Commit 040a0a37 "mutex: Add support for wound/wait style locks" used >> "!__builtin_constant_p(p == NULL)" but gcc 3.x cannot handle such expression >> correctly, leading to boot failure when built with CONFIG_DEBUG_MUTEXES=y. > So I completely forgot all about this, but wouldn't something like: > > !(__builtin_constant_p(p) && p == NULL) > > Not also work and generate the same code? > See earlier discussion. It was already answered why that was undesirable. ;) ~Maarten