From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755634AbXKDX2r (ORCPT ); Sun, 4 Nov 2007 18:28:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754215AbXKDX22 (ORCPT ); Sun, 4 Nov 2007 18:28:28 -0500 Received: from gw.goop.org ([64.81.55.164]:50521 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754176AbXKDX21 (ORCPT ); Sun, 4 Nov 2007 18:28:27 -0500 Message-ID: <472E557E.3010903@goop.org> Date: Sun, 04 Nov 2007 15:27:58 -0800 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.5 (X11/20070727) MIME-Version: 1.0 To: Linus Torvalds CC: "H. Peter Anvin" , Linux Kernel Mailing List , Thomas Gleixner , Ingo Molnar , Mikael Petterson , Eric Biederman Subject: Re: [GIT PULL] x86 setup: correct booting on 486DX4 References: <200711042259.lA4Mxa0n025210@tazenda.hos.anvin.org> In-Reply-To: X-Enigmail-Version: 0.95.5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds wrote: > I'm not entirely sure that it needs to be a long-jump, btw. I think any > regular branch is sufficient. You obviously *do* need to make the long > jump later (to reload %cs in protected mode), but I'm not sure it's needed > in that place. I forget the exact rules (but they definitely were > documented). Yes, it says it needs to be a far jmp or call (and if you enabled paging in the cr0 load, you need to identity-map the branch target). Having successfully broken the rules for a long time so far, maybe we can get away with still cutting corners... but it doesn't seem particularly worthwhile since we've been caught once. J