[SeaBIOS] SeaBIOS as EFI application

Jordan Justen jljusten at gmail.com
Sat Nov 10 20:30:39 CET 2012

On Sat, Nov 10, 2012 at 8:25 AM, Thorsten Glaser <tg at mirbsd.de> wrote:
> Kevin O'Connor dixit:
>>1 - Using SeaBIOS as a CSM.  The CSM spec is amazingly complex as
>>2 - Implementing in SeaBIOS a subset of the EFI OS interface so that
> Both aren’t really what I want.

It sounds like you definitely don't want 2, but you do want something
similar to 1. In a UEFI+CSM system, the CSM essentially provides the
environment that legacy BIOS based software can use.

>>To be clear though, neither of the above paths would enable you to
>>boot something like DOS on an existing UEFI system.  It may be
> Yeah. I was more thinking of having SeaBIOS be an EFI “OS”,
> just like the MirBSD bootloader is a Multiboot compliant “OS
> kernel”, and then take over the system and load the real OS,
> providing BIOS calls to it.

How do you generically deal with chipset memory protection in
0xc0000-0x100000? (Ie, shadow ram that Kevin mentioned.)

You may find that you need a 'chipset driver' to allow you to write
these regions. UEFI has the LegacyRegion protocol for this for CSM
systems, for example. But, in a non-CSM UEFI system, there is no need
for the LegacyRegion protocol.

It could be that in a post-CSM UEFI world that these regions will
generally just be set to RAM mode, but I wouldn't bet on it. It
certainly seems unlikely that you could rely on this for all UEFI

In OVMF we currently leave those regions in ROM mode.


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