From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161512AbXBOWSs (ORCPT ); Thu, 15 Feb 2007 17:18:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161478AbXBOWSr (ORCPT ); Thu, 15 Feb 2007 17:18:47 -0500 Received: from ftp.linux-mips.org ([194.74.144.162]:51412 "EHLO ftp.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161508AbXBOWSq (ORCPT ); Thu, 15 Feb 2007 17:18:46 -0500 Date: Thu, 15 Feb 2007 22:18:39 +0000 From: Ralf Baechle To: Andrew Morton Cc: Atsushi Nemoto , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Optimize generic get_unaligned / put_unaligned implementations. Message-ID: <20070215221839.GA14103@linux-mips.org> References: <20050830104056.GA4710@linux-mips.org> <20060306.203218.69025300.nemoto@toshiba-tops.co.jp> <20060306170552.0aab29c5.akpm@osdl.org> <20070214214226.GA17899@linux-mips.org> <20070214203903.8d013170.akpm@linux-foundation.org> <20070215143441.GA18155@linux-mips.org> <20070215135358.020781dd.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070215135358.020781dd.akpm@linux-foundation.org> User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 15, 2007 at 01:53:58PM -0800, Andrew Morton wrote: > > The whole union thing was only needed to get rid of a warning but Marcel's > > solution does the same thing by attaching the packed keyword to the entire > > structure instead, so this patch is now using his macros but using __packed > > instead. > > How do we know this trick will work as-designed across all versions of gcc > and icc (at least) and for all architectures and for all sets of compiler > options? > > Basically, it has to be guaranteed by a C standard. Is it? Gcc info page says: [...] `packed' The `packed' attribute specifies that a variable or structure field should have the smallest possible alignment--one byte for a variable, and one bit for a field, unless you specify a larger value with the `aligned' attribute. [...] Qed? Ralf