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From: Laurent Vivier <lvivier@redhat.com>
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Date: Tue, 12 Sep 2017 10:11:42 +0200
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Subject: Re: [Qemu-devel] [PATCH v2 2/3] hmp: fix "dump-quest-memory"
 segfault (arm)
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To: Peter Maydell <peter.maydell@linaro.org>, Thomas Huth <thuth@redhat.com>
Cc: QEMU Developers <qemu-devel@nongnu.org>, "Daniel P . Berrange" <berrange@redhat.com>, Cornelia Huck <cohuck@redhat.com>, David Gibson <david@gibson.dropbear.id.au>, qemu-arm <qemu-arm@nongnu.org>, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, "Dr . David Alan Gilbert" <dgilbert@redhat.com>, Greg Kurz <groug@kaod.org>

On 11/09/2017 18:40, Peter Maydell wrote:
> On 11 September 2017 at 15:45, Thomas Huth <thuth@redhat.com> wrote:
>> On 11.09.2017 16:39, Peter Maydell wrote:
>>> On 11 September 2017 at 15:20, Laurent Vivier <lvivier@redhat.com> wrote:
>>>> Commit fd5d23babf (hmp: fix "dump-quest-memory" segfault)
>>>> fixes the problem for i386, do the same for arm.
>>>>
>>>> Running QEMU with
>>>>     qemu-system-aarch64 -M none -nographic -m 256
>>>> and executing
>>>>     dump-guest-memory /dev/null 0 8192
>>>> results in segfault
>>>>
>>>> Fix by checking if we have CPU.
>>>>
>>>> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
>>>
>>> It seems a little arbitrary to assume that if there's no
>>> CPU what you wanted was a 32-bit little-endian dump.
>>>
>>> Why do we have a machine without a CPU anyway ?
>>
>> The "none" machine is always started without a default CPU.
> 
> If it has no CPU then how can we create a core dump for it?
> We don't (in theory) even know whether it's x86 or ARM.
> (One day we may support multiple CPU architectures in
> one QEMU binary...)
> 
> If the theory is hotplug-later then we're a bit stuck
> because we need to know information now that we can't
> know until the CPU is actually hotplugged.

As we have memory we should be able to dump memory, even without CPU.

But I can also do as proposed by Thomas and return -1 to cancel the dump
if there is no CPU.

Thanks,
Laurent