[lttng-dev] [RFC PATCH] Basic support of UST dynamic instrumentation

[Zifei Tong]

Hi,

I am writing to submit a patch set to implement basic support of UST
dynamic instrumentation.

Based on the discussion in previous thread  [1]:
Mathieu Desnoyers <mathieu.desnoyers at efficios.com> wrote:
> Basically, we enable an event targeting:
>
>   - an executable or a shared object,
>   - a symbol or offset within this executable or object.
>
> This would be the basic instrumentation mode that would allow
> dynamic instrumentation across all processes using the executable or
> .so.

I've changed the proposed command line interface as follows:

# lttng enable-event aname -u
Event options:
    --probe [object@](addr | symbol | symbol+offset)
                           Dynamic probe.
                           - userspace tracer requires specifying an
object to instrument.
                           - Addr and offset can be octal (0NNN...),
                             decimal (NNN...) or hexadecimal (0xNNN...)
    --function [object@](addr | symbol | symbol+offset)
                           Dynamic function entry/return probe.
                           - userspace tracer requires specifying an
object to instrument.
                           - Addr and offset can be octal (0NNN...),
                             decimal (NNN...) or hexadecimal (0xNNN...)

So the user need to provide a path of the executable of shared library
to instrument.

Example:
# lttng enable-event aevent -u --probe=/tmp/a.out at main
# lttng enable-event aevent -u --function=/tmp/a.out at main+0x42

The basic procedure implemented is:
After the user execute the lttng enable-event command, lttng-sessiond will send
the command to all registered applications. The applications will then check if
themselves are to be instrumented (they are the executable specified by user or
they loaded the shared library specified by user). If so, the app will
notify the
sessiond to do the actual instrumentation.

Two issues for now:
*  The patches now assume the event associated with the probe to instrument
is already registered. I am working on to eliminate this limitation.
*  Methods to instrument shared libraries are not implemented yet.

The patch set follows in separated mails. Please provide your comments.

Thank you!

[1] http://lists.lttng.org/pipermail/lttng-dev/2013-August/021056.html
--
Best Regards,
仝子飞 (Zifei Tong)