Re: [Qemu-devel] QEMU: DBT vs. Interpretation

[Laurent Desnogues]

On Mon, Jan 26, 2015 at 9:54 PM, Javier Picorel <address@hidden> wrote:
> Hi,
>
> We are trying to make QEMU deterministic for
> architectural simulation. In the absence of I/O,
> let’s say only executing user code or exceptions,
> is there any source of indeterminism (e.g., non
> deterministic compiler optimizations, TB indeterminism)
> of QEMU’s DBT versus a canonical interpreter? Thanks!

I have only hit two sources of variations:

- time;  for instance SPEC 2000 173.gcc dumps time at
  the end, so you'll get slightly different results each run

- environment variables which are parsed by the runtime
  at process start;  to get around that issue you'll have
  to reintroduce -ignore-environment which was removed
  some time ago (see commit
  fc9c54124d134dbd76338a92a91804dab2df8166)

A "canonical interpreter" would have the same issues.

HTH,

Laurent