[ipxe-devel] [Qemu-devel] Big real mode use in ipxe

Kevin O'Connor kevin at koconnor.net
Sun Aug 19 15:53:32 UTC 2012

On Sun, Aug 19, 2012 at 04:34:50PM +0100, Michael Brown wrote:
> On Sunday 19 Aug 2012 16:07:05 Avi Kivity wrote:
> > (and that seabios needs changes to either work in
> > big real mode, or to put the processor back into big real mode after
> > returning from a PMM service.
> If seabios switches into protected mode when performing a PMM service, then it 
> _must_ leave the segment limits at 4G when returning to real mode.  To do 
> otherwise will violate the PMM spec, and will break conforming clients such as 
> iPXE.

SeaBIOS does switch to 32bit mode during PMM calls and does switch to
16bit "big real" mode (segment limits set to 4G) on return.


More information about the ipxe-devel mailing list