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

["Blue Swirl" <blauwirbel@gmail.com>]

On 9/16/08, Edgar E. Iglesias <edgar.iglesias@axis.com> 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?