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

[Alexander Graf]

On 26.06.14 13:36, BALATON Zoltan wrote:
> 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.

Too bad.

> > 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.

That sounds odd. Why don't you just implement a tiny instruction 
emulator? We only need to catch stores here, no?


Alex