Re: [Qemu-devel] memory trace with qemu

[Eduardo Cruz]

Thanks for your awnsers. Stean, after I find the right place to capture the reads and writes I'll definitely try your trace tool.

Until now, this is what i found:

I am using the x86-64 target, and I know that, for instance, lots of reads pass here:

target-i386/translate.c ��gen_op_ld_T1_A0()

This function calls�gen_op_ld_v, that calls a tcg function according to the operand size.

Lets assume�tcg_gen_qemu_ld8u() is called, which is defined at tcg/tcg-op.h

Here I find myself lost again, because this function (in i386) calls�tcg_gen_op3i_i32, which APPARENTLY does nothing...

Where the code that access the main memory is being generated?

2010/7/24 Stefan Hajnoczi <address@hidden>

On Sat, Jul 24, 2010 at 3:17 AM, Yufei Chen <address@hidden> wrote:
> On Fri, Jul 23, 2010 at 2:15 PM, Stefan Hajnoczi <address@hidden> wrote:
>> On Fri, Jul 23, 2010 at 4:12 AM, Mulyadi Santosa
>> <address@hidden> wrote:
>>> Hi...
>>>
>>> On Fri, Jul 23, 2010 at 05:30, Eduardo Cruz <address@hidden> wrote:
>>>> Hello, I need qemu to keep track of all the memory access made by the guest,
>>>> including read, write and the instruction fetches.
>
> I don't think Qemu can provide cycle number information. But other
> information are all available.
>
>>>
>>> AFAIK there are lots of experiments on this and has produces working
>>> patches...at least from the posting of the creator. There is even a
>>> patch floating to start creating trace framework a while ago.
>>
>> Thanks Mulyadi, I think you are referring to the tracing work that
>> Prerna Saxena and I are doing. �Here is the documentation:
>>
>> http://repo.or.cz/w/qemu/stefanha.git/blob/tracing:/docs/tracing.txt
>>
>> The patches apply to qemu.git. �You can define trace events in the
>> trace-events file and then call them from places in the code. �There
>> is a script to pretty-print the binary trace file that QEMU produces.
>>
>> Eduardo, if you think this might be what you're looking for, please
>> give it a try. �I am on #qemu and #kvm IRC if you need any help. �Any
>> feedback will be valuable to us as we prepare these patches for
>> submission to qemu.git.
>>
>> I believe the tracing framework answers the "Any ideas of how I can
>> record these information with qemu?" part of your question :). �I
>> don't have experience in the TCG, so I can't give advice on how to
>> best get at the memory accesses, but I hope this helps you one step
>> further.
>>
>
> Can this framework trace memory access event? I guess this would be
> more difficult to do in KVM than in TCG.

No, it can't trace memory accesses. �It provides you with the ability
to put trace events into QEMU, but there is current no pre-defined
trace event for memory access.

If you find the right spot to in TCG it should be easy to add a trace
event there. �I agree, with KVM is would be more difficult and perhaps
defeat the point of KVM :).

Stefan

>> Stefan
>>
>>> perhaps you could dig a little deeper in qemu archieve....?
>>>
>>> --
>>> regards,
>>>
>>> Mulyadi Santosa
>>> Freelance Linux trainer and consultant
>>>
>>> blog: the-hydra.blogspot.com
>>> training: mulyaditraining.blogspot.com
>>>
>>>
>>
>>
>
>
>
> --
> Best regards,
> Chen Yufei
>

-- 
Eduardo Henrique Molina da Cruz
MSc student
Parallel and Distributed Processing Group
Federal University of Rio Grande do Sul (UFRGS)