From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265900AbUBSBXV (ORCPT ); Wed, 18 Feb 2004 20:23:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265983AbUBSBXV (ORCPT ); Wed, 18 Feb 2004 20:23:21 -0500 Received: from [218.5.74.208] ([218.5.74.208]:25518 "EHLO vhost.bizcn.com") by vger.kernel.org with ESMTP id S265900AbUBSBXO (ORCPT ); Wed, 18 Feb 2004 20:23:14 -0500 Message-ID: <40340EF4.4050409@greatcn.org> Date: Thu, 19 Feb 2004 09:18:44 +0800 From: Coywolf Qi Hunt Organization: GreatCN.org User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.5) Gecko/20031007 X-Accept-Language: en-us, en, zh MIME-Version: 1.0 To: root@chaos.analogic.com CC: Riley@Williams.Name, davej@suse.de, hpa@zytor.com, Linux kernel Subject: Re: [PATCH 2.4.24] Fix GDT limit in setup.S References: <403114D9.2060402@lovecn.org> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Richard B. Johnson wrote: > On Tue, 17 Feb 2004, Coywolf Qi Hunt wrote: > > >>Hello 2.4.xx hackers, >> >>In setup.S, i feel like that the gdt limit 0x8000 is not proper and it >>should be 0x800. How came 0x800 into 0x8000 in 2.4.xx code? Is there a >>story? It shouldn't be a careless typo. 256 gdt entries should be >>enough and since it's boot gdt, 256 is ok even if the code is run on SMP >>with 64 cpus. >> > > > The first element has nothing to do with the number of GDT entries. > It represents the LIMIT. Because the granularity bit is > set meaning 4 kilobyte pages and 0x8000 * 0x1000 = 0x8000000 > | | > | |_______ Page size > |______________ GDT value > This is the size of address space that is unity-mapped for boot. > > The granularity is also not the number of GDT entries. It > represents the length for which the GDT definition applies. > > Because this GDT is used only for booting, somebody decided that > there would never be any boot code beyond 2 GB so there was no > reason to make room for it. If you change the number to 0x0800, > you are declaring that neither the boot code nor any RAM-disk > combination will ever exceed 0x800 * 0x1000 = 0x800000 bytes. > Therefore you broke my imbedded system. Do not do this. > > >>At least the comment doesn't match the code. Either fix the code or fix >>the comment. We really needn't so many GDT entries. Let's use the intel >>segmentation in a most limited way. Below follows a patch fixing the code. >> >>I don't have the latest 2.4.24, but setup.S isn't changed from 2.4.23 to >>2.4.24. >> >>Regards, Coywolf >> Thank you for you kindly reply, though I really don not agree with you. But thanks very much, since you are the only one replying me. I CCed to all the 2.0 2.2 2.4 maintainers. -- Coywolf Qi Hunt Admin of http://GreatCN.org and http://LoveCN.org