[OpenBIOS] [Qemu-ppc] 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