Re: [Qemu-devel] env fields as TCG variables

[Edgar E. Iglesias]

On Tue, Sep 16, 2008 at 10:31:01PM +0300, Blue Swirl wrote:
> On 9/16/08, Edgar E. Iglesias <address@hidden> wrote:
> > On Tue, Sep 16, 2008 at 09:37:41PM +0300, Blue Swirl wrote:
> >  > I wonder if the following bug scenario is possible.
> >  >
> >  > Some of the env fields are accessible as TCG variables, like cpu_fsr
> >  > for Sparc floating point status register (%fsr), stored in the env
> >  > structure field env->fsr. When cpu_fsr is used in the generated code,
> >  > a host CPU register is allocated for this task. But env->fsr can be
> >  > modified directly in op_helper.c code. Isn't it then possible that the
> >  > register (which stores cpu_fsr) and the structure field in memory
> >  > (env->fsr) get out of sync?
> >  >
> >  > If this is true, no code outside the generated code should ever modify
> >  > or even read env fields that are also available as TCG variables. Or
> >  > do I miss something?
> >
> >
> > Hello,
> >
> >  IIRC:
> >  TCG writebacks before calling helpers. There used to be a bug with
> >  qemu_ld/qemu_st like the one you described but it was fixed a long
> >  time ago. I ran into that one with CRIS and avoided it for a while
> >  by calling a dummy helper before load/stores.
> 
> OK, this solves the main part of the problem. But what about code
> outside helpers, for example interrupt handling?

Hi Again, Im not sure but if I understand correctly:
Interrupts are only taken between TB's and TCG writebacks globals at the end of 
TBs.
MMU faults work by writebacking globals before loads/stores.

Best regards