Re: [Qemu-devel] [PATCH] Add e500 instructions dcblc, dcbtls and dcbtstl as no-op

[Alexander Graf]

On 30.06.2011, at 23:46, Scott Wood wrote:

> On Thu, 30 Jun 2011 23:34:37 +0200
> Alexander Graf <address@hidden> wrote:
> 
>> We could just keep an internal counter that memorizes how much memory is 
>> locked and sets the bit after exceeding the fake cache size.
> 
> And keep track of unlocks, decrementing the counter only if the address was
> already locked...  seems better to keep it simple and just be honest about
> the failure until a real need for trickery arises.
> 
>> The only problem I could see remaining is that CAR could potentially fail, 
>> as it can access addresses in cache directly that don't have to have 
>> underlying RAM mapped. However, I'd hope that only firmware does this and we 
>> usually don't execute real firmware in qemu :)
> 
> This is a case where it would be nice for the guest to see the failure
> indication, if we're lucky enough that it bothers to check.
> 
> But yeah, it's unlikely to happen outside of firmware.
> 
>> Also, lock set instructions seem to raise DSIs, so we need to generate some 
>> loads that don't go anywhere.
> 
> Yes.
> 
> Note that dcbtstls is treated as a store, which is a little trickier.

Not that much. It should be enough to simply do:

  st(addr, ld(addr));

no?


Alex