Re: [Qemu-ppc] [OpenBIOS] Apple's BootX

[Jd Lyons]

> On Jan 30, 2018, at 10:47 AM, Jd Lyons via OpenBIOS <address@hidden> wrote:
> 
> 
> 
>> On Jan 30, 2018, at 9:10 AM, BALATON Zoltan <address@hidden> wrote:
>> 
>> On Mon, 29 Jan 2018, Jd Lyons via OpenBIOS wrote:
>>> Ok, with a little help for Paul at the kvm-ppc mailing list, it seems the 
>>> issue maybe that the BootX or more likely mach_kernel it trying to write 
>>> something to or probe for an L3 cache.
>> 
>> With kvm could be but on TCG it doesn't seem that way. Enabling some SPR 
>> debug options in target/ppc/translate_init.c I see this (with qemu git HEAD 
>> without other patches):
>> 
>> $ ppc-softmmu/qemu-system-ppc -cpu G4 -d int
>> Write SPR 272 110 <= 07e00000
>> Read SPR 287 11f => 000c0209
>> Read SPR 25 019 => 07e00000
>> Read SPR 25 019 => 07e00000
>> Read SPR 287 11f => 000c0209
>> Raise exception at fff08978 => 00000003 (40000000)
>> Write SPR 273 111 <= 07df7ff0
>> Write SPR 274 112 <= 20000004
>> Read SPR 272 110 => 07e00000
>> Read SPR 273 111 => 07df7ff0
>> Read SPR 274 112 => 20000004
>> Read SPR 26 01a => fff08978
>> Read SPR 27 01b => 40000030
>> 
>> $ ppc-softmmu/qemu-system-ppc -cpu 7447a -d int
>> Write SPR 272 110 <= 07e00000
>> Read SPR 287 11f => 80030102
>> Read SPR 25 019 => 07e00000
>> Read SPR 25 019 => 07e00000
>> Read SPR 287 11f => 80030102
>> Raise exception at fff08978 => 0000004e (00)
>> 
>> So OpenBIOS gets unexpected exception very early right after reading the PVR 
>> so maybe it's a problem in OpenBIOS before it gets to what you're 
>> describing. Is this already fixed?
>> 
>> Regards,
>> BALATON Zoltan
>> 
>> -- 
>> OpenBIOS                 http://openbios.org/
>> Mailinglist:  http://lists.openbios.org/mailman/listinfo
>> Free your System - May the Forth be with you
> 
> It looks like in TCG mode that it tries to read these invalid spr’s
> 
> 1018
> 1011
> 1016
> 1012
> 
> This doesn’t cause a halt, as the kernel boots.
> 
> 

What I’m assuming is the kernel is trying to read the state of spr 1018 (r13), 
but it can’t read it. It does seem to exist for the 7447a it’s value is just 
zero( 0x00000000 ) and of course you can’t write anything there.

I don’t think the kernel is trying to write anything there, I think it’s just 
probing the state of the register to determine if the L3 cache exists. There 
are just too many references to the r13 in the xun source for me to figure out 
how to stop the kernel from trying to make a read here. Paul seems to suggest 
it could be fixed in KVM, but it seems like I could fix it in Qemu if I knew 
how to get Qemu to pass that spr( 1018 ) to the guest as readable with the 
value 0x00000000.

Would anyone be able to help me do that?  


> 
> 
> -- 
> OpenBIOS                 http://openbios.org/
> Mailinglist:  http://lists.openbios.org/mailman/listinfo
> Free your System - May the Forth be with you