[syslinux] Is it possible to chainload EXTLINUX from GRUB?
H. Peter Anvin
hpa at zytor.com
Tue Oct 24 15:23:02 PDT 2006
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.)
> 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.
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.
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