Re: [Qemu-ppc] MorphOS 4.x on QEMU

[BALATON Zoltan]

On Wed, 26 Feb 2014, Alexander Graf wrote:
> I'm fairly sure most people don't particularly have a good idea what's
> going wrong for you :).

That's OK, I expect not many people are interested in this but I wasn't 
sure that anyone actually reads these mails. My questions were not about 
MorphOS but about QEMU, openbios and PPC Macs so maybe people knowing 
these could help even if they don't know MorphOS.

> > zeroing the 0x80 address causes an exception problem.
>
> That's probably a NULL pointer exception. Your bootloader is trying to
> find something, doesn't find it, returns NULL, something else takes the
> return value as granted and accesses that pointer + 0x80.

I don't think so. The code I've quoted in my first message is all that 
runs up to this assignment from 0x400000 which is the base, start address 
of the boot loader. Before that everything that runs is part of openbios. 
Besides, as far as I can read ppc assembly I don't see where it could try 
to get a return address in this code:

0x00400058:  li      r22,0
0x0040005c:  li      r9,128
0x00400060:  mr      r26,r5
0x00400064:  mr      r25,r6
0x00400068:  stw     r22,0(r9)

which looks like a direct assignment to 0x80 to me. What am I missing? 
Could it be that on real hardware the boot loader is run with a different 
PID so the memory is not overlapping the interrupt vectors or on a Mac 
this address is not part of the interrupt vectors? First of all why does 
the bootloder try to set this address to zero? It makes no sense to me. Is 
there anything mapped there on a PPC Mac?

> So far PCI passthrough has only been done on IBM POWER (-M pseries) and
> Freescale e500  (-M ppce500) systems. I doubt MorphOS runs on either of
> them.

AFAIK, it does not. Apart from some PPC Macs it supports a few boards some 
of them with some Freescale parts but I need to check how similar is that 
to what QEMU already has. I'm starting to think that targeting these may 
be an easier route now because on the Mac it only supports some specific 
Radeon cards while on other boards some more may work too.

> Plus PCI passthrough is pretty hard to get right with TCG - so
> this is something I don't think anyone attempted so far.
>
> If you like to give it a go though, try to make something slightly more
> simple work first though :). VGA adapters are hell.

I did not mean to share a video card with the host but to have a second 
card dedicated to the guest of course. But it seems to be too big 
undertaking for me if noone else has tried that before. (And I'd need to 
dig up a compatible card first to try it.)

> There's a web page somewhere with lots of device tree dumps from systems
> all over the place. I don't have the link right now, but I'm sure Google
> knows more :).

I've tried to find that but so far I only could find ioregs dumps from 
Intel Macs. I'll keep trying to locate that page then.

Regards,
BALATON Zoltan