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Re: [Qemu-trivial] [Qemu-devel] [PATCH] tests: Fix 'make test' for i686

From: Peter Maydell
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] tests: Fix 'make test' for i686 hosts (buildregression))
Date: Fri, 7 Mar 2014 16:37:04 +0000

On 7 March 2014 16:17, Alex Bennée <address@hidden> wrote:
> Peter Maydell <address@hidden> writes:
>> I think TCG x86 FPU emulation has been a bit dodgy since
>> forever; it's a fair amount of work to go through and
>> fix everything up to be bitwise exact results versus
>> hardware and I think that nobody's cared enough about x86
>> emulation to do that...
> IIRC the behaviour is different depending on how much x87 vs SIMD FP you
> go through. FWIW the Transitive translator was able to do most FP ops
> with generated code (certainly on SPARC->x86_64) and only go to softfloat
> for some things. But you did need to disable the x87 to do it.
> But I get the impression that FP performance is currently "good enough"
> for what QEMU gets used for.

This is true but not particularly relevant to whether our
current implementation is actually buggy in the sense
of producing wrong results. We ripped out the code that
tried to implement FP natively a long time back, so
pure emulation is all we do now.

-- PMM

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