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Re: [Qemu-devel] env fields as TCG variables
From: |
Blue Swirl |
Subject: |
Re: [Qemu-devel] env fields as TCG variables |
Date: |
Tue, 16 Sep 2008 22:31:01 +0300 |
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?