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From: Peter Maydell <peter.maydell@linaro.org>
Date: Sun, 30 Nov 2014 10:20:19 +0000
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Subject: Re: [PATCH 5/7] KVM: arm64: guest debug, add support for single-step
To: Christoffer Dall <christoffer.dall@linaro.org>
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On 30 November 2014 at 10:10, Christoffer Dall
<christoffer.dall@linaro.org> wrote:
> In any case, I think it was related to how userspace observes the state
> of the CPU, because when you do the MMIO operation emulation in
> userspace, currently if you observe the PC though GET_ONE_REG, you'll
> see a PC pointing to the next instruction, not the one you're emulating
> which is strange.

Also if we ever add support for userspace to say "this MMIO should
fault" then we definitely need the PC-advance to happen afterwards,
not before.

> Not sure what the relation to a guest single-stepping itself was.

I think it just came up in the course of that discussion, because
single-step handling also needs to perform an action (clear PSTATE.SS)
as part of the "advance over this insn" operation. But I think that
you're right that doing the advance before dropping out to userspace
is no worse for singlestep than it is for any other case.

-- PMM
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