Re: [Qemu-devel] [PATCH 4/5] tcg: reorder removal from lists in tb_phys_invalidate

[Richard Henderson]

On 03/28/2016 01:58 PM, Paolo Bonzini wrote:
> On 28/03/2016 20:42, Sergey Fedorov wrote:
> > On 17/03/16 16:46, address@hidden wrote:
> > > First the translation block is invalidated, for which a simple write
> > > to tb->pc is enough.  This means that cpu-exec will not pick up anymore
> > > the block, though it may still execute it through chained jumps.  This
> > > also replaces the NULLing out of the pointer in the CPUs' local cache.
> >
> > Although, using 'tb->pc' to mark a TB as invalid is probably not such a
> > good idea. There may be some cases when PC could become equal to -1. For
> > example, ARMv6-M uses PC >= 0xFFFFFFF0 to perform exception return. So
> > we'd better introduce a separate 'tb->valid' or 'tb->invalid' flag.
>
> It is also possible to use tb->flags for that.  I suspect that all-ones
> tb flags is never valid, but it could also be a #define.

That might work by accident, but it might not.  You'd need to reserve a bit 
across all of the targets.


r~