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From devnull@lkml.org Fri Apr 26 09:33:46 2024 Delivery-date: Mon, 27 Nov 2006 14:00:30 +0000 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758221AbWK0N7H (ORCPT ); Mon, 27 Nov 2006 08:59:07 -0500 Received: from odyssey.analogic.com ([204.178.40.5]:38916 "EHLO odyssey.analogic.com") by vger.kernel.org with ESMTP id S1758219AbWK0N7E convert rfc822-to-8bit (ORCPT ); Mon, 27 Nov 2006 08:59:04 -0500 Received: from chaos.analogic.com ([10.112.50.11]) by phoenix.analogic.com with Microsoft SMTPSVC(6.0.3790.211); Mon, 27 Nov 2006 08:59:01 -0500 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-MimeOLE: Produced By Microsoft Exchange V6.5.7226.0 Received: from chaos.analogic.com (localhost [127.0.0.1]) by chaos.analogic.com (8.12.11/8.12.11) with ESMTP id kARDx1Jn004118; Mon, 27 Nov 2006 08:59:01 -0500 Received: (from linux-os@localhost) by chaos.analogic.com (8.12.11/8.12.11/Submit) id kARDwvQ1004117; Mon, 27 Nov 2006 08:58:57 -0500 X-OriginalArrivalTime: 27 Nov 2006 13:59:01.0906 (UTC) FILETIME=[3157FF20:01C7122C] content-class: urn:content-classes:message Subject: Re: failed 'ljmp' in linear addressing mode Date: Mon, 27 Nov 2006 08:58:57 -0500 Message-Id: In-Reply-To: <20061122234111.GA8499@srv.junsun.net> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: failed 'ljmp' in linear addressing mode Thread-Index: AccSLDFfxY0e7i58Siikd/2js3Qv8w== References: <20061122234111.GA8499@srv.junsun.net> From: "linux-os \(Dick Johnson\)" To: "Jun Sun" Cc: Reply-To: "linux-os \(Dick Johnson\)" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Nov 2006, Jun Sun wrote: > > I am plowing along as I am learning about the in'n'outs about i386. I am > totally stuck on this one. I would appreciate any help. > > As you can see, the function turns off paging mode (of course it > runs from identically mapped page) and tries to jump to an absolute > address at 0x10000000. It appears the machine would reboot when running > "ljmp" instruction. > > Any pointers? > > I was not too certain about the %cs, %ds business and did quite > a few experiments with different values but with no luck. > > Thanks in advance. > > Jun > > -------------------------- > > /* [JSUN] we will map this page into identity mapping before execution */ > .align 4096 > ENTRY(do_os_switching) > /* interrupt is disabled! */ > > /* the black magic, some copied form relocate_new_kernel, JSUN */ > /* Set cr0 to a known state: > * 31 0 == Paging disabled > * 18 0 == Alignment check disabled > * 16 0 == Write protect disabled > * 3 0 == No task switch > * 2 0 == Don't do FP software emulation. > * 0 1 == Proctected mode enabled > */ > > movl %cr0, %eax > andl $~((1<<31)|(1<<18)|(1<<16)|(1<<3)|(1<<2)), %eax > orl $(1<<0), %eax > movl %eax, %cr0 > > > /* JSUN, 0x11 was the boot up value for cr0. > movl $0x11, %eax > movl %eax, %cr0 > */ > > /* clear cr4 */ > movl $0, %eax > movl %eax, %cr4 > > /* why this? */ > jmp 1f > 1: > > /* clear cr3, flush TLB */ > movl $0, %eax > movl %eax, %cr3 > > /* > movl $(__KERNEL_DS),%eax > movl %eax,%ds > movl %eax,%es > movl %eax,%fs > movl %eax,%gs > movl %eax,%ss > */ > > ljmp $(__KERNEL_CS), $0x10000000 > I think it probably resets the instant that you turn off paging. To turn off paging, you need to copy some code (properly linked) to an area where there is a 1:1 mapping between virtual and physical addresses. A safe place is somewhere below 1 megabyte. Then you need to set up a call descriptor so you can call that code (you can ljump if you never plan to get back). You then need to clear interrupts on all CPUs (use a spin-lock). Once you are executing from the new area, you reset your segments to the new area. The call descriptor would have already set CS, as would have the long-jump. At this time you can turn off paging and flush the TLB. You are now in linear-address protected mode. Cheers, Dick Johnson Penguin : Linux version 2.6.16.24 on an i686 machine (5592.72 BogoMips). New book: http://www.AbominableFirebug.com/ _  **************************************************************** The information transmitted in this message is confidential and may be privileged. 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