Re: [Qemu-devel] Call Trace for QEMU functions

[Naman patel <naman321@gmail.com>]

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​Thanks Alex and Peter for this useful information. Looks like the stack
information is not available for this functions in QEMU 2.0.

Can someone explain me what happens when a guest OS calls "invlpg" on say
page swap out or a context switch? What exactly is the call flow and how
QEMU handles this instruction? Also is there anyway QEMU can send some data
back to the guest OS?

P.S. : Sorry if my questions look like generic queries but I am kinda of
stuck here.

On Thu, Jul 30, 2015 at 8:34 PM, Alex Bennée <alex.bennee@linaro.org> wrote:

>
> Peter Maydell <peter.maydell@linaro.org> writes:
>
> > On 30 July 2015 at 13:20, Naman patel <naman321@gmail.com> wrote:
> >> Hi,
> >>
> >>      I have compiled QEMU (2.0) for x86_64 on Fedora 22 with tracing
> enabled
> >> and the tracing option I chose was dtrace. I have this script called
> >> callTrace.stp in which I try and get the Call Trace of the function
> >> helper_invlpg and later tlb_flush.  But I am not able to get the
> function
> >> name of the caller function and the call trace depth is only limited to
> 2.
> >
> > The helper_invlpg function is called directly from code generated
> > by QEMU's built-in JIT, not from any other C function.
> >
> > If you use a newer version of QEMU than 2.0 then I think we have
> > fixed some of the stack frame information up so that you can
> > get a backtrace that looks like:
> >  * helper function
> >  * [generated code]
> >  * QEMU execution loop code that handles executing guest code
> >  * other QEMU functions
> >
> > This is not likely to be very useful for profiling why or when
> > we're calling a particular helper function, though.
>
> With the perf JIT patch you can get a better handle on the profile. I'll
> see if I can re-spin them tomorrow for the latest tree.
>
> >
> > thanks
> > -- PMM
>
> --
> Alex Bennée
>

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