Syslinux - Nov 2009 - Initial bootloader requirements of extlinux

I'm trying to understand what the extlinux bootloader code written into a 
partition needs to successfully start. I have a disk with four partitions, the 
second is marked active and contains a kernel, initrd and root FS and extlinux 
has been run on it. If I use mbr.bin as the initial bootloader the system 
boots fine.

I need this to work within an environment supplied by a third party. They have 
their own bootloader in the MBR and the above installation does not work. 
After leaving their bootloader all I get is 'Boot error'.

Looking at extlinux.asm it appears that it expects ES:DI to point to the 
partition entry and DL to contain the drive number. I've modified the MBR
code
to do this but the system still doesn't boot. Is there anything else that 
extlinux needs?

If I use grub instead the system does boot.

Thanks,
	Simon

On 11/06/2009 01:53 AM, Simon Rowe wrote:
> I'm trying to understand what the extlinux bootloader code written into
a
> partition needs to successfully start. I have a disk with four partitions,
the
> second is marked active and contains a kernel, initrd and root FS and
extlinux
> has been run on it. If I use mbr.bin as the initial bootloader the system 
> boots fine.
> 
> I need this to work within an environment supplied by a third party. They
have
> their own bootloader in the MBR and the above installation does not work. 
> After leaving their bootloader all I get is 'Boot error'.
> 
> Looking at extlinux.asm it appears that it expects ES:DI to point to the 
> partition entry and DL to contain the drive number. I've modified the
MBR code
> to do this but the system still doesn't boot. Is there anything else
that
> extlinux needs?
> 
DS:SI, not ES:DI.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Simon Rowe wrote:
>
> Are these conventions documented anywhere, any references would 
> greatly help
> in getting the author to fix their code,
>
You might enjoy http://www.ata-atapi.com/hiwmbr.html

- Shao Miller

On Wednesday 11 November 2009 16:33:03 Shao Miller wrote:
> You might enjoy http://www.ata-atapi.com/hiwmbr.html
Thanks, I had found a similar disassembly of the Win95 MBR code

http://home.att.net/~rayknights/pc_boot/w95b_mbr.htm

that again shows SI being set up. I had hoped to come across something more 
official looking, like the T13 doc about the equivalent GPT behaviour.

http://www.t13.org/Documents/UploadedDocuments/docs2009/e09127r1-
EDD-4_Hybrid_MBR_support.pdf

Hopefully the above will be sufficient to get a fix,

	Simon