From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422932AbXBPAn0 (ORCPT ); Thu, 15 Feb 2007 19:43:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422934AbXBPAn0 (ORCPT ); Thu, 15 Feb 2007 19:43:26 -0500 Received: from ftp.linux-mips.org ([194.74.144.162]:58703 "EHLO ftp.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422932AbXBPAnX (ORCPT ); Thu, 15 Feb 2007 19:43:23 -0500 Date: Fri, 16 Feb 2007 00:43:17 +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: <20070216004317.GA18987@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> <20070215221839.GA14103@linux-mips.org> <20070215153823.239fd616.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070215153823.239fd616.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 03:38:23PM -0800, Andrew Morton wrote: > hm. So if I have > > struct bar { > unsigned long b; > } __attribute__((packed)); > > struct foo { > unsigned long u; > struct bar b; > }; > > then the compiler can see that foo.b.b is well-aligned, regardless of the > packedness. > > Plus some crazy people compile the kernel with icc (or at least they used > to). What happens there? A quick grep for __attribute__((packed)) and __packed find around 900 hits, I'd probably find more if I'd look for syntactical variations. Some hits are in arch/{i386,x86_64,ia64}. At a glance it seems hard to configure a useful x86 kernel that doesn't involve any packed attribute. I take that as statistical proof that icc either has doesn't really work for building the kernel or groks packing. Any compiler not implementing gcc extensions is lost at building the kernel but that's old news. Ralf