Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758734Ab1E0Iyj (ORCPT ); Fri, 27 May 2011 04:54:39 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:45667 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752710Ab1E0Iyi (ORCPT ); Fri, 27 May 2011 04:54:38 -0400 Date: Fri, 27 May 2011 09:54:14 +0100 From: Russell King - ARM Linux To: Catalin Marinas Cc: Nicolas Pitre , Will Deacon , =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= , lkml , ak@linux.intel.com, Andrew Morton , sam@ravnborg.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] ARM: Do not allow unaligned accesses when CONFIG_ALIGNMENT_TRAP Message-ID: <20110527085414.GP24876@n2100.arm.linux.org.uk> References: <20110524171331.GA2941@arm.com> <20110525111405.GA12010@e102109-lin.cambridge.arm.com> <20110525124348.GA2340@arm.com> <1306429854.26735.9.camel@e102144-lin.cambridge.arm.com> <20110526215101.GL24876@n2100.arm.linux.org.uk> <20110527083806.GA21100@e102109-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110527083806.GA21100@e102109-lin.cambridge.arm.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1260 Lines: 27 On Fri, May 27, 2011 at 09:38:08AM +0100, Catalin Marinas wrote: > OK, I tried this now: > > -fconserve-stack: we get unaligned accesses on the stack because the > newer versions of gcc turned unaligned accesses on by default. > > -fconserve-stack -mno-unaligned-access: the stack variables are aligned. > We probably get the benefit of -fconserve-stack as well. > > So as per the initial post in this thread, we could have > -mno-unaligned-access on ARM always on (when CONFIG_ALIGNMENT_TRAP). As > Nicolas suggested, we could compile some files with -munaligned-access > (and maybe -fno-conserve-stack). > > I raised this with the gcc guys so they are looking into it. But it > really doesn't look like a gcc bug as long as -mno-unaligned-access is > taken into account. Ok, we need to check one last thing, and that's what the behaviour is with -mno-unaligned-access and packed structures (such as the ethernet header). If it makes no difference, then I suggest we always build with -mno-unaligned-access. -- 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/