Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761448AbXJYHTA (ORCPT ); Thu, 25 Oct 2007 03:19:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756804AbXJYHSv (ORCPT ); Thu, 25 Oct 2007 03:18:51 -0400 Received: from cantor.suse.de ([195.135.220.2]:60733 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755469AbXJYHSu (ORCPT ); Thu, 25 Oct 2007 03:18:50 -0400 From: Andi Kleen To: Nick Piggin Subject: Re: Is gcc thread-unsafe? Date: Thu, 25 Oct 2007 09:15:50 +0200 User-Agent: KMail/1.9.1 Cc: Linux Kernel Mailing List , Linus Torvalds References: <200710251324.49888.nickpiggin@yahoo.com.au> In-Reply-To: <200710251324.49888.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200710250915.50675.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1366 Lines: 34 On Thursday 25 October 2007 05:24, Nick Piggin wrote: > Basically, what the gcc developers are saying is that gcc is > free to load and store to any memory location, so long as it > behaves as if the instructions were executed in sequence. This case is clearly a bug, a very likely code pessimization. I guess it wasn't intentional, just an optimization that is useful for local register values doing too much. > I guess that dynamically allocated memory and computed pointers > are more difficult for gcc to do anything unsafe with, because > it is harder to tell if a given function has deallocated the > memory. Often accesses happen without function calls inbetween. Also I think newer gcc (not 3.x) can determine if a pointer "escapes" or not so that might not protect against it. > Any thoughts? We don't have much choice: If such a case is found it has to be marked volatile or that particular compiler version be unsupported. It might be useful to come up with some kind of assembler pattern matcher to check if any such code is generated for the kernel and try it with different compiler versions. -Andi - 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/