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From: Peter Maydell <peter.maydell@linaro.org>
To: sraasch@gmail.com
Cc: QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: Extracting PC information from QEMU/KVM during single-step
Date: Thu, 24 Jun 2021 17:22:54 +0100	[thread overview]
Message-ID: <CAFEAcA8eADzVVMVZHaHBC9Lm09aVvC5Wwj-q7nLkKoRUn3vS5A@mail.gmail.com> (raw)
In-Reply-To: <CA+5M2MC9q5RTNYh2YTan_g0TMAkNc0YD_Nx0OV7ze4v7dYdP9w@mail.gmail.com>

On Wed, 23 Jun 2021 at 22:10, Steven Raasch <sraasch@gmail.com> wrote:
> I have used KVM to create a snapshot of a windows-10 guest running a graphics-intensive app. The *original* issue is that the app does not execute correctly when re-started from the snapshot using TCG (it doesn't crash, but it doesn't run correctly, either).

I'm not sure that taking a snapshot with KVM and then resuming under TCG
is really tested. So I'm not very surprised that it doesn't work.

> I'm setting DEBUG & single-step modes by calling cpu_single_step() from the top of kvm_vcpu_thread_fn().
> in kvm_cpu_exec() I wait until I get a KVM_EXIT_DEBUG signal before logging the instruction.

If your app can cope with the slowdown involved in taking a VM exit
after every instruction (which will be massive), then it can probably
also handle the extra overhead on top of that of the gdbstub communication
protocol. So it's probably simplest just to connect to QEMU's gdbstub and
do the single-stepping that way.

The other approach to this would be to see if intel's perf monitor
stuff (which I know nothing about) has some kind of execution-trace
capture support and if that works when passing through the PMU to a
KVM guest.

thanks
-- PMM


  parent reply	other threads:[~2021-06-24 16:25 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-23 20:14 Extracting PC information from QEMU/KVM during single-step Steven Raasch
2021-06-24  1:45 ` Alexander Bulekov
2021-06-24 13:49   ` Steven Raasch
2021-06-24 14:41     ` Alexander Bulekov
2021-06-24 16:22 ` Peter Maydell [this message]
2021-06-24 17:08   ` Steven Raasch
2021-06-24 18:51     ` Peter Maydell
2021-06-24 19:36       ` Steven Raasch

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