linux-kernel - Re: [PATCH 12/12] i386 boot: Add an ELF header to bzImage

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Date:	Fri, 06 Oct 2006 06:56:03 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...l.org>
Cc:	vgoyal@...ibm.com,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Reloc Kernel List <fastboot@...ts.osdl.org>, ak@...e.de,
	horms@...ge.net.au, lace@...kratochvil.net, hpa@...or.com,
	magnus.damm@...il.com, lwang@...hat.com, dzickus@...hat.com,
	maneesh@...ibm.com
Subject: Re: [PATCH 12/12] i386 boot: Add an ELF header to bzImage

Andrew Morton <akpm@...l.org> writes:

> On Thu, 05 Oct 2006 09:29:42 -0600
> ebiederm@...ssion.com (Eric W. Biederman) wrote:
>
>> 
>> In the lazy programmer school of fixes.
>> 
>> I haven't really tested this in any configuration.
>> But reading video.S it does use variable in the bootsector.
>> It does seem to initialize the variables before use.
>> But obviously something is missed.
>> 
>> By zeroing the uninteresting parts of the bootsector just after we
>> have determined we are loaded ok.  We should ensure we are
>> always in a known state the entire time. 
>> 
>> Andrew if I am right about the cause of your video not working
>> when you set an enhanced video mode this should fix your boot
>> problem.
>> 
>> Singed-off-by: Eric Biederman <ebiederm@...ssion.com>
>> 
>> diff --git a/arch/i386/boot/setup.S b/arch/i386/boot/setup.S
>> index 53903a4..246ac88 100644
>> --- a/arch/i386/boot/setup.S
>> +++ b/arch/i386/boot/setup.S
>> @@ -287,6 +287,13 @@ # Check if an old loader tries to load a
>>  loader_panic_mess: .string "Wrong loader, giving up..."
>>  
>>  loader_ok:
>> +# Zero initialize the variables we keep in the bootsector
>> +	xorw	%di, %di
>> +	xorb	%al, %al
>> +	movw	$497, %cx
>> +	rep
>> +	stosb
>> +
>>  # Get memory size (extended mem, kB)
>>  
>>  	xorl	%eax, %eax
>
> That fixed the vga=0x263 crash.

Good.  We still have to be paranoid and address HPA's missing cld issues,
But otherwise it looks like we are in good shape.

Eric


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