Re: [Qemu-devel] Re: Missing singlestep for already-translated code?

[Jan Kiszka <jan.kiszka@siemens.com>]

Aurelien Jarno wrote:
> Jun Koi a écrit :
>> On Wed, Apr 14, 2010 at 12:28 AM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>>> Alexander Graf wrote:
>>>> On 13.04.2010, at 15:36, Jan Kiszka wrote:
>>>>
>>>>> Jun Koi wrote:
>>>>>> Hi,
>>>>>>
>>>>>> I am looking into the singlestep command in monitor interface, and it
>>>>>> seems that we only take into account the singlestep flag when we are
>>>>>> translating code.
>>>>>> So for the already-translated code, we will miss singlestep?
>>>>> This feature is broken. For TCG, it should at least flush the
>>>>> translation buffer, and for KVM it has to enable single-stepping in the
>>>>> kernel. That's what happens automatically when you call cpu_single_step.
>>>>> I guess 'singlestep' wants to be somehow orthogonal to this. But this is
>>>>> the wrong approach.
>>>>>
>>>>> Does anyone actually used this feature or still does so? It looks fairly
>>>>> redundant to me, kind of a poor-man's gdb front-end as part of the
>>>>> monitor console.
>>>> Not sure what it does, but I use -singlestep quite a lot to get register dumps for instructions when using -d cpu.
>>> Ah, "singlestep" is not about stopping the VM after each instruction but
>>> about limiting the TB length to a single instruction. Badly named and
>>> poorly documented.
>>>
>>> In that case, the dynamic switch should already be fine by adding a
>>> tb_flush() on enable. Still, someone should also patch at least the docs.
>>>
> 
> What's the real point of flushing the tb to get it retranslated again?
> It will be retranslated in the exact same way.

Nope. AFAIU, 'singlestep' will enforce single-instruction TBs.

Jan

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