From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1KLf5u-0001u2-PW
	for qemu-devel@nongnu.org; Wed, 23 Jul 2008 10:13:30 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1KLf5u-0001tO-4l
	for qemu-devel@nongnu.org; Wed, 23 Jul 2008 10:13:30 -0400
Received: from [199.232.76.173] (port=52471 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1KLf5t-0001tH-U7
	for qemu-devel@nongnu.org; Wed, 23 Jul 2008 10:13:30 -0400
Received: from yx-out-1718.google.com ([74.125.44.152]:44827)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <anthony@codemonkey.ws>) id 1KLf5t-0006bs-NA
	for qemu-devel@nongnu.org; Wed, 23 Jul 2008 10:13:29 -0400
Received: by yx-out-1718.google.com with SMTP id 3so416020yxi.82
	for <qemu-devel@nongnu.org>; Wed, 23 Jul 2008 07:13:29 -0700 (PDT)
Message-ID: <48873C69.4040808@codemonkey.ws>
Date: Wed, 23 Jul 2008 09:12:57 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [BUG] QEMU BIOS - El Torito no emulation boot address
	incorrect seg:off
References: <4886FD90.6040409@utu.fi>
In-Reply-To: <4886FD90.6040409@utu.fi>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org

Jarno Rajala wrote:
> Hello
>
> I believe I've located a minor bug in QEMU BIOS. According to the El 
> Torito specification the no emulation mode should load the boot code 
> to the real mode address seg:0 and start executing from there. 
> However, QEMU jumps to 0:seg*16, which is the same absolute address, 
> but wrong segment:offset.

It could be a bug, but then again, specifications aren't always 
correct.  At any rate, the BIOS code is part of the Bochs project so I 
would suggest bringing it up there.

Regards,

Anthony Liguori

> The QEMU BIOS version I have is
>
> QEMU BIOS - build: 02/13/08
> $Revision: 1.194 $ $Date: 2007/12/23 19:46:27 $
> Options: apmbios pcibios eltorito rombios32
>
> The following boot code illustrates the problem. It prints JJ to the 
> top of the screen on a real PC, but prints JA instead on QEMU. (The 
> boot image is set to load into the segment 0x7c8)
>
> test_code:
>    call .call
> .call:
>    pop bx
>    mov ax,cs
>    shl ax,4
>    add ax,bx
>   .l1
>    cmp ax,0x7c83
>    jne .l1
>      mov ax,0xb800
>    mov es,ax
>    mov [es:0],word 0x074a
>      mov ax,cs
>    cmp ax,0x7c8
>    jne .l2
>    mov [es:2],word 0x074a
>    jmp .loopy
> .l2
>    cmp ax,0
>    jne .loopy
>    mov [es:2],word 0x0741
>     .loopy:
>    jmp .loopy
>
> Jarno Rajala
>
>
>