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Re: [Qemu-devel] QEMU: DBT vs. Interpretation
From: |
Laurent Desnogues |
Subject: |
Re: [Qemu-devel] QEMU: DBT vs. Interpretation |
Date: |
Wed, 28 Jan 2015 16:10:02 +0100 |
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