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

From: Dale R. Worley
Subject: Re: [Qemu-discuss] QEMU: DBT vs. Interpretation
Date: Tue, 27 Jan 2015 21:51:04 -0500

Javier Picorel <address@hidden> writes:
> We are trying to make QEMU deterministic for 
> architectural simulation. In the absence of I/O, 
> let's say only 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'm not sure exactly what information you're trying to obtain.  Given
that most CPU architectures have multiple implementations, and many of
those have complex internal operations, it's difficult to make an
emulator deterministic in any way other than "its behavior conforms to
the architecture specification".

If you have an architecture whose implementation is fixed, you could
probably add instrumentation to the QEMU code generator to update the
counters in accordance with the implementation, so you could count the
number of memory cycles or whatever...


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