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

From: Alexander Graf
Subject: Re: [Qemu-ppc] [OpenBIOS] Running client with MMU off
Date: Thu, 26 Jun 2014 13:43:12 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

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?


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