Re: [Qemu-devel] memory trace with qemu

[Yufei Chen]

On Mon, Jul 26, 2010 at 6:21 AM, Eduardo Cruz <address@hidden> wrote:
> 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?

Please take a look at tcg_out_qemu_ld and tcg_out_qemu_st, also take a
look at tcg_out_op.

> 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)
>
>



-- 
Best regards,
Chen Yufei