Re: [Qemu-ppc] [PATCH 4/6] openpic: don't crash on a register access without a CPU context

[Scott Wood]

On 12/14/2012 06:35:12 AM, Alexander Graf wrote:
> On 14.12.2012, at 03:12, Scott Wood wrote:
>
> > If we access a register via the QEMU memory inspection commands  
> (e.g.
> > "xp") rather than from guest code, we won't have a CPU context.
> > Gracefully fail to access the register in that case, rather than
> > crashing.
>
> Can't we set cpu_single_env in the debug memory access case? I'm not  
> sure this is the only device with that problem, and by always having  
> cpu_single_env available we would completely get rid of the whole bug  
> category.

So, how would we go about doing this?  cpu_single_env is declared as  
thread-local storage.  Even if there's some way to deliberately inspect  
a different thread's local storage, I don't see how you'd get it to  
work automatically without changing all those drivers (and are there  
really that many that care about the CPU?) -- and we might break other  
places that already check whether cpu_single_env is NULL.

FWIW, hw/pc.c does pretty much the same thing as this patch in  
cpu_get_current_apic().

-Scott