Re: [Qemu-devel] BIOS calls in 16bit protected mode

[Natalia Portillo <claunia@claunia.com>]

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Hi Kevin,

Long time ago I read about OS/2 calling 16-bit protected mode BIOS, but the documentation didn't specified if this was constrained to the separate protected mode BIOS included by PS/2 systems or the real mode BIOS included by the same PS/2 systems and the whole rest of PC computers.

Regards,
Natalia Portillo

El 14/06/2012, a las 04:13, Kevin O'Connor escribió:

> Hi,
> 
> I am trying to determine if there are legacy applications or operating
> systems that invoke standard BIOS real-mode interrupt handlers while
> in 16bit protected mode.  (The legacy real-mode entry points - like
> "int 0x13" - not the declared 16bit protected mode entry points
> defined by the PnP and APM specs.)
> 
> I am considering changes to SeaBIOS that would make 16bit protected
> mode callers much less likely to work.  (Specifically, enhancing
> SeaBIOS to use memory in the e-segment which is unlikely to be mapped
> in protected mode.)
> 
> Most documents I've seen state that calling the real-mode entry points
> in protected mode will not work.  Though, I am aware that the PCI BIOS
> spec specifically requires this support for calls to "int 0x1a
> ah=0xb1".
> 
> The advantage of making these changes is that it will allow SeaBIOS to
> use notably less stack space and therefore be more compatible with old
> applications that call the BIOS with very little stack space.  For
> example, these changes enable DOS 1.0 to boot and run under SeaBIOS.
> 
> What would really help is pointers to applications and/or program
> images that use 16bit protected mode calls to real-mode entry points.
> Specifications or documents detailing valid or invalid uses would also
> be helpful.
> 
> For those that are willing to run tests, one can compare the standard
> SeaBIOS v1.7.0 image (for KVM/QEMU) at:
> 
> http://git.seabios.org/downloads/get/bios.bin-1.7.0.gz
> 
> to a test image with the new code at:
> 
> http://git.seabios.org/downloads/get/bios.bin-test-20120613.gz
> 
> Thanks,
> -Kevin
> 


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