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Date: Sat, 4 Jun 2011 11:01:20 +0100
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From: Peter Maydell <peter.maydell@linaro.org>
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Subject: Re: [Qemu-devel] [PATCH] target-arm: Move VLD/VST multiple into
 helper functions
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, patches@linaro.org

On 3 June 2011 21:47, Aurelien Jarno <aurelien@aurel32.net> wrote:
> Does this patch fixes a real issue (ie most probably a crash), or it is
> just to make the arm target compliant with the README?

I haven't actually generated a test case which would make qemu
abort, but it shouldn't be hard to do so.

> Two remarks there:
> - The guidance in tcg/README is probably true for complex helpers in the
> =C2=A0sense of doing a lot of logic/arithmetic operations for which the T=
CG
> =C2=A0instruction set if not really rich and for which the compiler can d=
o
> =C2=A0a lot better. When the instruction is emulated mostly by load/store
> =C2=A0ops, there isn't much possible optimizations left.

Yes. The 96 op limit to avoid overrunning the buffer is a hard
one, though.

> - Your patch calls the slow version of the _mmu functions, which doesn't
> =C2=A0use the QEMU TLB. It is therefore normal to expect a slow down.

...even for linux-user mode? That doesn't use softmmu...

Anyway, this patch is on my list to rework when I can figure
out what the right approach to it is.

-- PMM