From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from moutng.kundenserver.de ([212.227.126.171]:60212 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752547AbXFPLVk (ORCPT ); Sat, 16 Jun 2007 07:21:40 -0400 From: Arnd Bergmann Subject: Re: [PATCH] Introduce compat_u64 and compat_s64 types Date: Sat, 16 Jun 2007 13:21:35 +0200 References: <200706150159.l5F1xNgM000459@hera.kernel.org> <1181986686.25228.639.camel@pmac.infradead.org> <200706161226.40875.arnd@arndb.de> In-Reply-To: <200706161226.40875.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200706161321.35940.arnd@arndb.de> Sender: linux-arch-owner@vger.kernel.org To: David Woodhouse Cc: Benjamin Herrenschmidt , Linux Kernel Mailing List , Dave Airlie , linux-arch@vger.kernel.org, Andrew Morton List-ID: On Saturday 16 June 2007, Arnd Bergmann wrote: > On Saturday 16 June 2007, David Woodhouse wrote: > > Will GCC know that it needs to emit code to handle that (mis)alignment? > > I've tested this with gcc-4.0.3, and it does the right thing, which > is to split a 4 byte aligned 64 bit load/store into two 32 bit accesses, > if you pass -mstrict-align. I just realized this was correct but slightly misleading. On powerpc, we don't set the 'attribute((aligned(4)))' on compat_64, so there is never a reason to handle the misalignment, even though it would work. On x86_64, misaligned loads are always ok, so gcc never needs to care about this, even attribute((packed)) does not cause byte access here. Arnd <><