From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754990Ab3JQLC2 (ORCPT ); Thu, 17 Oct 2013 07:02:28 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49121 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754944Ab3JQLC0 (ORCPT ); Thu, 17 Oct 2013 07:02:26 -0400 Date: Thu, 17 Oct 2013 13:02:15 +0200 From: Peter Zijlstra To: Maarten Lankhorst Cc: Tetsuo Handa , 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. Message-ID: <20131017110215.GN2675@laptop.programming.kicks-ass.net> References: <201310171945.AGB17114.FSQVtHOJFOOFML@I-love.SAKURA.ne.jp> <20131017105243.GM2675@laptop.programming.kicks-ass.net> <525FC1DD.4030205@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <525FC1DD.4030205@canonical.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 17, 2013 at 12:54:21PM +0200, Maarten Lankhorst wrote: > 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. ;) OK; I forgot if we covered that particular option.. I so hate this patch; but I'm afraid we'll have to take it :-/