[lttng-dev] Clang plugin providing automatic application instrumentation

[Zifei Tong]

Hi,

Please check the set_tracepoint() function in liblttng-ust/tracepoint.c

    /*
     * Sets the probe callback corresponding to one tracepoint.
     */
    static void set_tracepoint(struct tracepoint_entry **entry, struct
tracepoint *elem, int active);

I think probes are connected to tracepoints when user enable
corresponding events.

Hope that helps.

Zifei Tong

On Tue, Mar 18, 2014 at 5:08 PM, wen qun wang <xiaoxiao046 at gmail.com> wrote:
> Hi,everyone.At first ,thanks for jeremie's help. I have completed toolchain
> to gain  an understanding of how the different pieces fit together.Then, I'm
> going to through the studying the demo(/lttng-ust-2.4.0/doc/examples/demo)
> of lttng-ust to understand the working principle of lttng.But now,I am in
> trouble.
> In /lttng-ust-2.4.0/doc/examples/demo/demo.c
>
> ##################
> tracepoint(ust_test_demo2,done,42)
> ###################
>
> I found the definition of tracepoint in
> /lttng-ust-2.4.0/include/lttng/tracepoint.h
>
> ############################################################
> #define tracepoint(provider, name, ...)    \
> do {    \
> STAP_PROBEV(provider, name, ## __VA_ARGS__);    \
> if (caa_unlikely(__tracepoint_##provider##___##name.state)) \
> __tracepoint_cb_##provider##___##name(__VA_ARGS__); \
> } while (0)
> #################################################################
>
> then i found the definition of
> "__tracepoint_cb_##provider##___##name(__VA_ARGS__)" in
> /lttng-ust-2.4.0/include/lttng/tracepoint.h line 158
>
> ########################################################################
> void __tracepoint_cb_##_provider##___##_name(_TP_ARGS_PROTO(__VA_ARGS__)) \
> { \
> struct tracepoint_probe *__tp_probe; \
> \
> if (caa_unlikely(!TP_RCU_LINK_TEST())) \
> return; \
> tp_rcu_read_lock_bp(); \
> __tp_probe =
> tp_rcu_dereference_bp(__tracepoint_##_provider##___##_name.probes); \
> if (caa_unlikely(!__tp_probe)) \
> goto end; \
> do { \
> void (*__tp_cb)(void) = __tp_probe->func; \
> void *__tp_data = __tp_probe->data; \
> \
> URCU_FORCE_CAST(void (*)(_TP_ARGS_DATA_PROTO(__VA_ARGS__)), __tp_cb) \
> (_TP_ARGS_DATA_VAR(__VA_ARGS__)); \
> } while ((++__tp_probe)->func); \
> end: \
> tp_rcu_read_unlock_bp(); \
> }
> ####################################################################
>
> It seems that "__tracepoint_##_provider##___##_name"  in
> "__tracepoint_##_provider##___##_name.probes" is a struct of tracepoint.
> we can found the macro TRACEPOINT_EVENT was used in
> "lttng-ust-2.4.0\doc\examples\demo\ust_tests_demo.h".And the struct of
> tracepoint was defined by the macro TRACEPOINT_EVENT.But the
> __tracepoint_##_provider##___##_name.probes was set to null.
>
> #################################################
> \lttng-ust-2.4.0\include\lttng\tracepoint.h line 342
> #define _DEFINE_TRACEPOINT(_provider, _name, _args) \
> extern int __tracepoint_provider_##_provider; \
> static const char __tp_strtab_##_provider##___##_name[] \
> __attribute__((section("__tracepoints_strings"))) = \
> #_provider ":" #_name; \
> struct tracepoint __tracepoint_##_provider##___##_name \
> __attribute__((section("__tracepoints"))) = \
> { \
> __tp_strtab_##_provider##___##_name, \
> 0, \
> NULL, \---------------------------------------------->here is the probes.
> _TRACEPOINT_UNDEFINED_REF(_provider), \
> _TP_EXTRACT_STRING(_args), \
> { }, \
> }; \
> static struct tracepoint * __tracepoint_ptr_##_provider##___##_name \
> __attribute__((used, section("__tracepoints_ptrs"))) = \
> &__tracepoint_##_provider##___##_name;
> ###################################################################
>
> so i want to know that how the probes of the tracepoint struct  should be
> initialized,I can't find the source code.
> My english is poor,i hope you can understand what i mean. Thank you very
> much.
>
>
>
>
>
>
> 2014-03-15 9:24 GMT+08:00 为王 <xiaoxiao046 at gmail.com>:
>>
>> thank you very much
>>
>>
>> 2014-03-15 1:35 GMT+08:00 Jérémie Galarneau
>> <jeremie.galarneau at efficios.com>:
>>
>>> On Wed, Mar 12, 2014 at 6:05 AM, 为王 <xiaoxiao046 at gmail.com> wrote:
>>> > Hi All,I am a graduate student from Beijing University of Posts and
>>> > Telecommunications. Due to my
>>> > experience in windows kernel development and debugging technique,I am
>>> > very
>>> > interested in the lttng project.I want to make a contribution for the
>>> > Clang
>>> > plugin providing automatic application instrumentation after reading
>>> > the
>>> > project ideas for gsoc2014.I am also interested in reverse engineering
>>> > and
>>> > binary hack.
>>> > The codes of lttng project have been downloaded for reading.Due to its
>>> > large
>>> > amount,i couldn't figure out a good way to understand it.So,i want to
>>> > konw
>>> > how should i proceed further.
>>>
>>> You should start by trying the complete toolchain to gain an
>>> understanding of how the different pieces fit together. I wouldn't
>>> suggest simply jumping into the code.
>>>
>>> Have a look at the guidelines posted on our GSoC 2014 wiki for more
>>> information on how to submit a proposal [1].
>>>
>>> Let us know if you have more specific questions.
>>>
>>> Jérémie
>>>
>>> [1]
>>> https://bugs.lttng.org/projects/lttng/wiki/Google_Summer_of_Code_2014#Guidelines-for-students-applying-to-GSoC
>>>
>>> > My english is poor,i hope you can understand what i mean. Thank you
>>> > very
>>> > much.
>>> >
>>> > _______________________________________________
>>> > lttng-dev mailing list
>>> > lttng-dev at lists.lttng.org
>>> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>>> >
>>>
>>>
>>>
>>> --
>>> Jérémie Galarneau
>>> EfficiOS Inc.
>>> http://www.efficios.com
>>
>>
>
>
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