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Date: Thu, 7 Apr 2011 18:31:06 +0300
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] How does the QEMU load the binary files bios.bin
	and vgabios-cirrus.bin?
Message-ID: <20110407153106.GA7100@redhat.com>
References: <BANLkTiniHnWOAhhs4kz60dWOnVPO1x0GBw@mail.gmail.com>
	<4D9DBC05.8010400@codemonkey.ws>
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Bei Guan <gbtju85@gmail.com>, QEMU Developers <qemu-devel@nongnu.org>

On Thu, Apr 07, 2011 at 08:28:37AM -0500, Anthony Liguori wrote:
> On 04/07/2011 03:22 AM, Bei Guan wrote:
> >Hi,
> >
> >I have some questions about the qemu's bios. How does the QEMU
> >load the binary files bios.bin and vgabios-cirrus.bin? Which
> >function or code file need I to pay more attention to?
> >
> >For the loading of vgabios-cirrus.bin and bios.bin, I just trace
> >them into the same funciton rom_add_file() in hw/loader.c. Is it
> >the right function, which loads the bioses?
> >
> >And then another question, how qemu give the control to bios when
> >the bios file is loaded? Maybe this question is not in the scope
> >of qemu, however, can you give me some cue point.
> 
> I had some stuff written up locally so I posted it to the wiki at
> http://wiki.qemu.org/Documentation/Platforms/PC
> 
> The x86 architecture defines the initial state of the chip to have
> the CS register have a base of 0xF000 and an IP of 0xFFF0.  The
> result is that the actual memory address of the first instruction
> falls at the end of the BIOS ROM segment.  This is the entry point
> to the BIOS.
> 
Actually after reset on x86 IP=0x0000fff0, CS=0xf000, CS.BASE= 0xffff0000,
CS.LIMIT=0xffff. So the execution begins at 0xfffffff0 where ROM is
mapped initially.

> The VGABIOS is treated like any other option ROM and is initialized
> during option ROM scanning.
> 
> Regards,
> 
> Anthony Liguori
> 
> >Any reply are appreciated. Thanks.
> >
> >Gavin
> >
> >
> >
> >
> 

--
			Gleb.