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

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Date:	Thu, 5 Oct 2006 23:59:09 -0700
From:	Andrew Morton <akpm@...l.org>
To:	ebiederm@...ssion.com (Eric W. Biederman)
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

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.
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