Re: [Qemu-devel] Re: PC machine types switched to SeaBIOS/gPXE

[Anthony Liguori <anthony@codemonkey.ws>]

Kevin O'Connor wrote:
> I traced this down, and it looks like there is a series of subtle bugs
> that led to this situation.
>
> The bug causing the boot to fail is that gPXE didn't update its
> checksum.  This was supposed to be fixed in gPXE commit f16668d, but
> it looks like gPXE either regressed or the e1000 driver is special in
> some way.
>
> The reason SeaBIOS commit a5826b5a exposes this issue, is that commit
> a5826b5a broke SeaBIOS' PMM support - the gPXE bug only shows up when
> PMM is not available.
>
> So, why did commit a5826b5a break PMM?  This appears to be some weird
> interaction with gcc and its "-fwhole-program -combine" options.  One
> of the variables (ZoneTmpHigh) is incorrectly marked by gcc as being
> local instead of global after commit a5826b5a.  Unfortunately, instead
> of getting an error, the build proceeded and had a bogus reference to
> the ZoneTmpHigh variable - which caused PMM allocations to fail even
> when there was memory.
>
> I've reorganized the build slightly to work around this problem with
> "-combine".  I've also updated the SeaBIOS linker scripts so that they
> will cause a build failure if a similar issue arises in the future.
> The latest SeaBIOS git should have this all working again (even with
> the current e1000 gPXE).
>   

Thanks for tracking this down Kevin!

Regards,

Anthony Liguori