[syslinux] Is it possible to chainload EXTLINUX from GRUB?

[H. Peter Anvin]

Gavin D. Smith wrote:
>> You're assuming that just because GRUB and LILO can be loaded that it 
>> is all done correctly.  GRUB and LILO might not rely on, for example, 
>> the DS:SI pointer (given their design methodology I would almost 
>> assume they don't.)
>>
>> For debugging, I would run this in an simulator and set a breakpoint 
>> at 0:7C00h.  This will be hit several times, one of which will be 
>> EXTLINUX entry; at this point examine the registers, and the memory 
>> pointed to by DS:SI (16 bytes) and ES:DI (64 bytes or so.)
>>
>>     -hpa
>>
> 
> Well I finally managed to create a disk image for use in a simulator and 
> have managed to recreate the behaviour. I can indeed view these 
> registers, however I don't know how to interpret these registers or the 
> memory to which they point. If I knew what they were meant to contain 
> then I would know that GRUB was at fault and could complain to them. I 
> can send terminal logs to this list to show the contents of these 
> registers if that would be helpful.
> 

Yes, please.

The registers are supposed to have the following values:

DL is supposed to have the drive number.
DS:SI is supposed to point to the 16-byte partition entry, which 
typically should be located in memory between address 0x600 and 0x800.
ES:DI is supposed to point to the $PnP header.

	-hpa