[Skiboot] Skiboot on qemu questions

Marty E. Plummer hanetzer at startmail.com
Fri Oct 9 14:59:37 AEDT 2020

On Fri, Oct 09, 2020 at 02:20:35PM +1100, Oliver O'Halloran wrote:
> On Fri, Oct 9, 2020 at 1:51 PM Marty E. Plummer <hanetzer at startmail.com> wrote:
> >
> > Hello all.
> >
> > Once again dusting off my coreboot work, making fairly good progress I
> > think (at least when running against a virtualized system via LeGoater's
> > qemu powernv target) and was a bit curious about a few things.
> >
> > In the context of running skiboot in qemu, is it 'considered' emulated?
> > As in, will it hit hypervisor exceptions? Currently I'm catching
> > excpetions 0xe00 and 0xe40 when jumping from romstage to ramstage, which
> > are both hypervisor exceptions. Wondering if I should be worried about
> > this. What about skiboot on real hardware?
> The powernv model emulates real hardware. When entering skiboot the
> CPU is in hypervisor real mode so illegal instructions will trap to
> 0xe40 to allow the hypervisor (that'd be you in this case) to emulate
> the instruction if it wants to. You shouldn't be taking a HDSI (0xe00)
> unless you turned on the MMU though so that's a bit odd. If the MMU is
> off it might be a bug in the model.
'you in this case' means the firmware (coreboot) I'm running?
I don't recall explicitly enabling MMU but this is all very early work,
so perhaps I did.

So 0xe40 illegal instructions, got it. Should have RTFM'd a bit more but
I'm pretty excited about current progress and glazed over a bit.
> > Some info and teaserish: https://i.imgur.com/07d2Q0y.png
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