Re: status grub2 port of grub-legasy map command

[Christian Franke <Christian.Franke@t-online.de>]

Vladimir 'phcoder' Serbinenko wrote:
>>
>> Do not do this. Some BIOS functions (like ah=08h) return data in dl.
>> Clients should not expect data in registers to be preserved across
>> interrupt calls. I don't know if there is something like a 8086/PC-BIOS
>> ABI document that we can find to confirm the non-preservation of dl, but
>> the FreeDOS MBR should be fixed then.
>>     
> Thank you for pointing ah=8 function
> AFAIK there is no normative reference. The source which was mainly
> used for long years is helppc and it states following:
> 	- registers DS, BX, CX and DX are preserved
> (http://heim.ifi.uio.no/~stanisls/helppc/int_13.html)
> But now this reference is terribly outdated.
> SeaBIOS preserves %dl too
>   

T13 EDD provides a probably more up to date documentation of int13.

There was no requirement to preserve registers is in EDD (2000) and 
EDD-2 (2002). It appeared in EDD-3 (2004) and is still in first EDD-4 
draft (2009):

"The values in all registers that are not explicitly defined in the 
following sections shall be preserved at the completion of each function 
call"
 From Section 8 of: BIOS Enhanced Disk Drive Services - 3 (T13/1572D 
Revision 3)

Fortunately, T13 docs are (unlike T10 and SATA-IO) still publicly available:
http://www.t13.org/Documents/MinutesDefault.aspx?DocumentType=4&DocumentStage=2

-- 
Regards,
Christian Franke