From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756511AbYCNQdY (ORCPT ); Fri, 14 Mar 2008 12:33:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753407AbYCNQdQ (ORCPT ); Fri, 14 Mar 2008 12:33:16 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:54474 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751276AbYCNQdQ (ORCPT ); Fri, 14 Mar 2008 12:33:16 -0400 Date: Fri, 14 Mar 2008 09:31:38 -0700 From: Arjan van de Ven To: Yan Cc: linux-kernel@vger.kernel.org Subject: Re: 2.6.22.6 - Discrepancy between running and on-disk kernels Message-ID: <20080314093138.22861a55@laptopd505.fenrus.org> In-Reply-To: <54b90fdf0803140908k44bee3a2gbf4187ae40dad4b3@mail.gmail.com> References: <54b90fdf0803140751m71935a09r9b039ca6eb124f4d@mail.gmail.com> <20080314090049.346d7428@laptopd505.fenrus.org> <54b90fdf0803140908k44bee3a2gbf4187ae40dad4b3@mail.gmail.com> Organization: Intel X-Mailer: Claws Mail 3.2.0 (GTK+ 2.12.5; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 14 Mar 2008 12:08:16 -0400 Yan wrote: > Can you point me to where in the source that self-patching happens? I > tried grep'ing > through the source for anything relevant, and came out empty handed. in the apply_alternatives() function > > -yan > > On Fri, Mar 14, 2008 at 12:00 PM, Arjan van de Ven > wrote: > > On Fri, 14 Mar 2008 10:51:43 -0400 > > Yan wrote: > > > > > Hello, > > > > > > I have been trying to compare the code from the on-disk > > > compressed kernel that was booted and the running kernel > > > extracted from /dev/kmem. I extracted the kernel's code from the > > > disk image by stripping the head.S and similar and gunzipping > > > it, and extracted the kernel from /dev/kmem by reading data > > > between _text and _etext symbol offsets. > > > > > > I then ran both through a disassembler and diff'ed the outputs. > > > Predictably, the disassembly was similar, but not identical. Some > > > instructions (e.g. bts) had a 'lock' prefix, where as others had > > > a 'nop' in its place. > > > > > > There were other differences with some instructions like mfence. > > > Everything else matched just fine, the differences were mostly in > > > memory-referencing instructions. > > > > > > My question is, what can be changing the kernel between being on > > > static storage and being loaded? > > > > the kernel code is self-patching, it gets modified to match your > > system during boot time. So you cannot assume that the kernel on > > disk and the kernel in memory are identical. > > (Same goes for modules) > > -- If you want to reach me at my work email, use arjan@linux.intel.com For development, discussion and tips for power savings, visit http://www.lesswatts.org