From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757946AbYEDVLM (ORCPT ); Sun, 4 May 2008 17:11:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753313AbYEDVK6 (ORCPT ); Sun, 4 May 2008 17:10:58 -0400 Received: from terminus.zytor.com ([198.137.202.10]:33248 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753162AbYEDVK6 (ORCPT ); Sun, 4 May 2008 17:10:58 -0400 Message-ID: <481E258C.20003@zytor.com> Date: Sun, 04 May 2008 14:07:24 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Arjan van de Ven CC: "Maciej W. Rozycki" , Thomas Gleixner , jamal , Suresh Siddha , Ingo Molnar , LKML , Jan Beulich Subject: Re: i387/FPU init issues... References: <1209810775.6972.37.camel@localhost> <481CA40A.7040906@zytor.com> <481CC5CD.8060205@zytor.com> <481E1B89.8020708@linux.intel.com> In-Reply-To: <481E1B89.8020708@linux.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Arjan van de Ven wrote: >> >> It has retroactively been added to the documented list for all P6 core >> chips - that should mean it works on all of them. The most common >> reason for not documenting something (other than various Pure Evil NDA >> schemes) is that it hasn't been properly verified. However, >> verification can be done a posteori. > > the other reason is that certain groups of "unknown" opcodes will act as > NOP. > Which for this purpose is .. exactly the right thing retroactive > Specifically, I believe the P6 added a whole class of instructions which would act as NOP's if used on older chips. It has been used for prefetch instructions, etc. At some point, the 0F 1F /0 group was declared to be NOP, and nothing else, for all future. -hpa