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NAME | SYNOPSIS | DESCRIPTION | BUGS | RESOURCES | COPYRIGHTS | THANKS | AUTHORS | SEE ALSO | COLOPHON |
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LTTNG-UST-CYG-PRO(3) LTTng Manual LTTNG-UST-CYG-PRO(3)
lttng-ust-cyg-profile - Function tracing (LTTng-UST helper)
Compile your application with compiler option -finstrument-
functions.
Launch your application by preloading liblttng-ust-cyg-profile-
fast.so for fast function tracing:
$ LD_PRELOAD=liblttng-ust-cyg-profile-fast.so my-app
Launch your application by preloading liblttng-ust-cyg-profile.so
for slower, more verbose function tracing:
$ LD_PRELOAD=liblttng-ust-cyg-profile.so my-app
When the liblttng-ust-cyg-profile.so or the liblttng-ust-cyg-
profile-fast.so library is preloaded before a given application
starts, all function entry and return points are traced by
LTTng-UST (see lttng-ust(3)), provided said application was
compiled with the -finstrument-functions compiler option.
See lttng(1) to learn more about how to control LTTng tracing
sessions.
Function tracing with LTTng-UST comes in two flavors, each one
providing a different trade-off between performance and
robustness:
liblttng-ust-cyg-profile-fast.so
This is a lightweight variant that should only be used where
it can be guaranteed that the complete event stream is
recorded without any missing events. Any kind of duplicate
information is left out.
At each function entry, the address of the called function is
recorded in an LTTng-UST event. Function exits are recorded
as another, empty LTTng-UST event.
See the Fast function tracing section below for the complete
list of emitted events and their fields.
liblttng-ust-cyg-profile.so
This is a more robust variant which also works for use cases
where events might get discarded, or not recorded from
application startup. In these cases, the trace analyzer needs
extra information to be able to reconstruct the program flow.
At each function entry and exit, the address of the called
function and the call site address are recorded in an
LTTng-UST event.
See the Verbose function tracing section below for the
complete list of emitted events and their fields.
Usage
To use LTTng-UST function tracing, you need to make sure the
sources of your application are compiled with the -finstrument-
functions compiler option.
It might be necessary to limit the number of source files where
this option is used to prevent excessive amount of trace data to
be generated at run time. Usually, there are additional compiler
flags that allow you to specify a more fine-grained selection of
function instrumentation.
For each instrumented function, the executable will contain calls
to profiling function hooks (after function entry, named
__cyg_profile_func_enter(), and just before function exit, named
__cyg_profile_func_exit()).
By preloading (using the LD_PRELOAD environment variable) one of
the provided shared libraries, these profiling hooks get defined
to emit LTTng events (as described below).
Note
Using this feature can result in a massive amount of trace
data to be generated by the instrumented application.
Application run time is also considerably affected. Be
careful on systems with limited resources.
Fast function tracing
The following LTTng-UST events are available when using liblttng-
ust-cyg-profile-fast.so. Their log level is set to
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_FUNCTION.
lttng_ust_cyg_profile_fast:func_entry
Emitted when an application function is entered, or more
specifically, when __cyg_profile_func_enter() is called.
Fields:
┌────────────┬───────────────────┐
│ Field name │ Description │
├────────────┼───────────────────┤
│ func_addr │ Function address. │
└────────────┴───────────────────┘
lttng_ust_cyg_profile_fast:func_exit
Emitted when an application function returns, or more
specifically, when __cyg_profile_func_exit() is called.
This event has no fields. Since the liblttng-ust-cyg-profile-
fast.so library should only be used when it can be guaranteed
that the complete event stream is recorded without any
missing events, a per-thread, stack-based approach can be
used on the trace analyzer side to match function entry and
return events.
Verbose function tracing
The following LTTng-UST events are available when using liblttng-
ust-cyg-profile.so. Their log level is set to
LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_FUNCTION.
lttng_ust_cyg_profile:func_entry
Emitted when an application function is entered, or more
specifically, when __cyg_profile_func_enter() is called.
Fields:
┌────────────┬─────────────────────────┐
│ Field name │ Description │
├────────────┼─────────────────────────┤
│ func_addr │ Function address. │
├────────────┼─────────────────────────┤
│ call_site │ Address from which this │
│ │ function was called. │
└────────────┴─────────────────────────┘
lttng_ust_cyg_profile:func_exit
Emitted when an application function returns, or more
specifically, when __cyg_profile_func_exit() is called.
Fields:
┌────────────┬─────────────────────────┐
│ Field name │ Description │
├────────────┼─────────────────────────┤
│ func_addr │ Function address. │
├────────────┼─────────────────────────┤
│ call_site │ Address from which this │
│ │ function was called. │
└────────────┴─────────────────────────┘
If you encounter any issue or usability problem, please report it
on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-
ust>.
• LTTng project website <http://lttng.org>
• LTTng documentation <http://lttng.org/docs>
• Git repositories <http://git.lttng.org>
• GitHub organization <http://github.com/lttng>
• Continuous integration <http://ci.lttng.org/>
• Mailing list <http://lists.lttng.org> for support and
development: lttng-dev@lists.lttng.org
• IRC channel <irc://irc.oftc.net/lttng>: #lttng on
irc.oftc.net
This library is part of the LTTng-UST project.
This library is distributed under the GNU Lesser General Public
License, version 2.1 <http://www.gnu.org/licenses/old-
licenses/lgpl-2.1.en.html>. See the COPYING
<https://github.com/lttng/lttng-ust/blob/v2.14/COPYING> file for
more details.
Thanks to Ericsson for funding this work, providing real-life use
cases, and testing.
Special thanks to Michel Dagenais and the DORSAL laboratory
<http://www.dorsal.polymtl.ca/> at École Polytechnique de
Montréal for the LTTng journey.
LTTng-UST was originally written by Mathieu Desnoyers, with
additional contributions from various other people. It is
currently maintained by Mathieu Desnoyers
<mailto:mathieu.desnoyers@efficios.com>.
lttng-ust(3), lttng(1), gcc(1), ld.so(8)
This page is part of the LTTng-UST (LTTng Userspace Tracer)
project. Information about the project can be found at
⟨http://lttng.org/⟩. It is not known how to report bugs for this
man page; if you know, please send a mail to man-pages@man7.org.
This page was obtained from the tarball fetched from
⟨https://lttng.org/files/lttng-ust/⟩ on 2024-06-14. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
LTTng 2.14.0-pre 06/07/2024 LTTNG-UST-CYG-PRO(3)
Pages that refer to this page: lttng-ust(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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