Re: [Qemu-ppc] [OpenBIOS] Running client with MMU off

[BALATON Zoltan]

On Thu, 26 Jun 2014, Alexander Graf wrote:
> On 26.06.14 13:20, BALATON Zoltan wrote:
> > On Thu, 26 Jun 2014, Alexander Graf wrote:
> > > You could enable write protection on the first page before you enter the 
> > > payload. Then you could unprotect it and disable interrupts as soon as 
> > > someone wrote to it. I guess that'd be a pretty solid hack.
> >
> > Good idea, I'll look into this. But 0x00-0xff is reserved for operating 
> > system use and MorphOS does write to 0x80 before touching the vectors 
> > (that's why I can't just check from the DSI handler). Can I selectively 
> > enable writes on a write protected page? (I'll need to read about it some 
> > more.)
>
> Not easily. You could emulate the 0x80 write maybe. Is it too early if you 
> just disable DR/IR on the 0x80 touch?

Definitely too early as this is the first thing it does.

> I don't think any other OS really accesses these ranges, but only time 
> will tell ;).

Don't know, according to previous replies they may. Then how about always 
clearing the translation for page zero the next time our handler is called 
so I always get a new exception when it's accessed? (I have to add it for 
the access to succeed but I may remove it at the next possible occasion.) 
In the lack of a better idea I'll try this.

Regards,
BALATON Zoltan