[lttng-dev] get function names with lttng-ust-cyg-profile

[Christophe Bédard]

Hi,

Babeltrace is doing exactly what it should as far as I know.
>

yes, but babeltrace *can* provide the information if:

* ip and vpid contexts are enabled (for userspace), e.g.

$ lttng add-context --userspace --type=ip --type=vpid

* LTTng state dump events are enabled, e.g.

$ lttng enable-event --userspace 'lttng_ust_statedump:*'


see this (from bt2 but it also applies to bt1):
https://babeltrace.org/docs/v2.0/man7/babeltrace2-filter.lttng-utils.debug-info.7/#doc-lttng-prereq

Note that the Python bindings for babeltrace don't provide/expose this
debug info.


Christophe

On Tue, 23 Jun 2020 at 11:12, Matthew Khouzam via lttng-dev <
lttng-dev at lists.lttng.org> wrote:

> Hi,
>
> You have the pointers that are traced. Babeltrace is doing exactly what it
> should as far as I know.
>
> You could use the command 'nm' to get your symbols and look them up. I am
> sure Babeltrace can do this from a python level. You could also use a GUI
> based trace viewer to get the information.
>
> Hope that helps.
> Matthew
> ------------------------------
> *From:* lttng-dev <lttng-dev-bounces at lists.lttng.org> on behalf of Liu,
> Changcheng via lttng-dev <lttng-dev at lists.lttng.org>
> *Sent:* Tuesday, June 23, 2020 10:37 AM
> *To:* lttng-dev at lists.lttng.org <lttng-dev at lists.lttng.org>
> *Cc:* changcheng.liu at intel.com <changcheng.liu at intel.com>
> *Subject:* [lttng-dev] get function names with lttng-ust-cyg-profile
>
> Hi all,
>    I'm trying to use lttng-ust-cyg-profile to trace program.
>    Does anyone know how to get function names and offset through
> lttng-ust-cyg-profile?
>
>    In below example, the babeltrace could only get the function entry/exit
> value.
>    1. Source program: instrument.c
>          1 #include <stdio.h>
>          2
>          3 int add3(int val) {
>          4         return val + 3;
>          5 }
>          6
>          7 int main(int argc, char **argv) {
>          8     int x = 4;
>          9
>         10     puts("Press Enter to continue...");
>         11     getchar();
>         12
>         13     x = add3(x);
>         14
>         15     return 0;
>         16 }
>
>    2. build source code:
>         $ gcc -g -finstrument-functions instrument.c -o instrument
>
>    3. run program:
>        $ LD_PRELOAD=/usr/lib/x86_64-linux-gnu/liblttng-ust-cyg-profile.so
> ./instrument
>
>    4. start trace process:
>        trace at trace:~/cc$ sudo lttng create instrument
>        Session instrument created.
>        Traces will be output to
> /root/lttng-traces/instrument-20200623-222917
>
>        trace at trace:~/cc$ sudo lttng enable-channel user_func_trace
> --userspace
>        UST channel user_func_trace enabled for session instrument
>
>        trace at trace:~/cc$ sudo lttng enable-event --userspace
> lttng_ust_cyg_profile:func_entry --channel user_func_trace
>        UST event lttng_ust_cyg_profile:func_entry created in channel
> user_func_trace
>        trace at trace:~/cc$ sudo lttng enable-event --userspace
> lttng_ust_cyg_profile:func_exit --channel user_func_trace
>        UST event lttng_ust_cyg_profile:func_exit created in channel
> user_func_trace
>
>        trace at trace:~/cc$ sudo lttng start
>        Tracing started for session instrument
>
>        trace at trace:~/cc$ sudo lttng destroy
>        Destroying session instrument..
>        Session instrument destroyed
>
>        trace at trace:~/cc$ sudo babeltrace
> /root/lttng-traces/instrument-20200623-222917
>        [22:29:55.388607059] (+?.?????????) trace
> lttng_ust_cyg_profile:func_entry: { cpu_id = 2 }, { addr = 0x5625C88B01A9,
> call_site = 0x5625C88B0237 }
>        [22:29:55.388612293] (+0.000005234) trace
> lttng_ust_cyg_profile:func_exit: { cpu_id = 2 }, { addr = 0x5625C88B01A9,
> call_site = 0x5625C88B0237 }
>        [22:29:55.388613215] (+0.000000922) trace
> lttng_ust_cyg_profile:func_exit: { cpu_id = 2 }, { addr = 0x5625C88B01EE,
> call_site = 0x7FE40BD5C0B3 }
>
> B.R.
> Changcheng
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