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

[Aurelien Jarno]

Jan Kiszka a écrit :
> Aurelien Jarno wrote:
>> Jun Koi a écrit :
>>> On Wed, Apr 14, 2010 at 12:28 AM, Jan Kiszka <address@hidden> 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.
> 

Ah ok, you mean it flushes the already translate TB. It makes sense now.


-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net