[SeaBIOS] Is the SeaBIOS ELF 32 bit entry point a supported interface?

Kevin O'Connor kevin at koconnor.net
Wed May 11 01:36:50 CEST 2011

On Tue, May 10, 2011 at 01:47:34PM +0100, Ian Campbell wrote:
> Hi,
> It looks like it is but I just thought I should check, is starting
> SeaBIOS via the ELF entry point (post32 in romlayout.S) rather than via
> the 16 bit reset vector valid from the SeaBIOS point of view?

It is valid - all coreboot users enter via the post32 stub.

> I'm considering it as an option for supporting SeaBIOS inside a Xen HVM
> (AKA fully virtualised) guest. Currently Xen loads "hvmloader" as the
> initial code to run within the guest. hvmloader does some initial setup,
> copies the BIOS (previously ROMBIOS but there is now very early support
> for SeaBIOS too) into the right place and then trampolines to the 16 bit
> entry point. However almost all of the initial setup is (or at least
> seems like it will end up being once I've checked it all out) ROMBIOS
> specific so I am considering the option of just loading SeaBIOS directly
> in place of hvmloader.

That's interesting.  Some questions - how will Xen obtain the address
of post32 - will it use the bios.bin.elf file?  On CPU reset / S3
resume (if supported at all), will Xen also call post32 or do a
regular real-mode entry?


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