From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750775AbWATKC5 (ORCPT ); Fri, 20 Jan 2006 05:02:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750778AbWATKC5 (ORCPT ); Fri, 20 Jan 2006 05:02:57 -0500 Received: from public.id2-vpn.continvity.gns.novell.com ([195.33.99.129]:19835 "EHLO emea1-mh.id2.novell.com") by vger.kernel.org with ESMTP id S1750775AbWATKC4 (ORCPT ); Fri, 20 Jan 2006 05:02:56 -0500 Message-Id: <43D0C361.76F0.0078.0@novell.com> X-Mailer: Novell GroupWise Internet Agent 7.0 Date: Fri, 20 Jan 2006 11:02:57 +0100 From: "Jan Beulich" To: "Andy Whitcroft" , "Andi Kleen" Cc: "Andreas Schwab" , "Linux Kernel Mailing List" Subject: Re: warning: read-write constraint -- 2.6.15-git8 onwards References: <43CE881A.1060403@shadowen.org> <200601190403.59205.ak@suse.de> In-Reply-To: <200601190403.59205.ak@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Looking at the official 3.4.x, 4.0.x, and the prerelease 4.1 sources I can't see such a warning, nor am I getting it with 3.3.3 when building on SLES9 (which makes me assume unmodified 3.3.3 doesn't have this either). I thus wonder whether the compiler used there has an extra, ill patch (after all there's generally nothing wrong for a read-write constraint to only allow memory on x86). Jan >>> Andi Kleen 19.01.06 04:03:58 >>> On Wednesday 18 January 2006 19:25, Andy Whitcroft wrote: > It seems that the following commit causes a bunch of warnings out of > most of the files in the kernel tree (see below for examples). Backing > this out seems to cure them? > Compiled with: > > gcc version 3.3.4 (Debian 1:3.3.4-6sarge1) > > -apw > > CC arch/x86_64/kernel/process.o > include/asm/bitops.h: In function `default_idle': > include/asm/bitops.h:65: warning: read-write constraint does not allow a > register > include/asm/bitops.h:65: warning: read-write constraint does not allow a > register > include/asm/bitops.h:30: warning: read-write constraint does not allow a > register > include/asm/bitops.h:30: warning: read-write constraint does not allow a > register I only tested with gcc 4.0 and 4.1 prereleases where it worked just fine. __asm__ __volatile__( LOCK_PREFIX "btrl %1,%0" :"+m" (ADDR) :"dIr" (nr)); I tried to covert them from +m to explicit input/output arguments ("=m" (ADDR) : "0" (ADDR)) to fix your compiler but with that I get the the same warning as you with 3.4 with 4.0. Don't know how else it could be written. Ok one could just pass the address and do a full memory clobber, but that would be a overly large sledgehammer for the problem. Jan or Andreas - do you have any suggestions how to fix this or should we revert back to the old (technically wrong) state which was __asm__ __volatile__( LOCK_PREFIX "btrl %1,%0" :"=m" (ADDR) :"dIr" (nr)); Thanks, -Andi