[ipxe-devel] ipxe/seabios: segment register initialization

Michael Brown mcb30 at ipxe.org
Sun Feb 14 17:36:38 GMT 2016


On 14/02/16 15:53, Michael S. Tsirkin wrote:
>> That's for execution of a PXE NBP, rather than a (SAN-booted) disk boot
>> sector.
>
> I actually thought the initial post was about iPXE calling NBP (starting
> at location 07C00h) with a non-zero DS, not about booting from disk.

The initial post mentioned a "boot sector which works just fine when 
loaded directly from BIOS, but doesn't work when loaded by iPXE".  That 
can only be referring to a disk boot sector, not a PXE NBP.  (For a 
start, the BIOS has no way to directly load a PXE NBP.)

> Rephrasing the original question,

It's not a rephrasing; it's an entirely different question.

> do you think %DS should be zeroed when NBP is called then?

Not according to the PXE spec.

As far as I can tell, the initial value of %ds is undefined for both a 
PXE NBP and a BIOS boot sector.

Michael


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