LTTNG-UST-DL(3) LTTng Manual LTTNG-UST-DL(3)
NAME
lttng-ust-dl - Dynamic linker tracing (LTTng-UST helper)
SYNOPSIS
Launch your application by preloading liblttng-ust-dl.so:
$ LD_PRELOAD=liblttng-ust-dl.so my-app
DESCRIPTION
When the liblttng-ust-dl.so library is preloaded before a given
application starts, it causes all calls to dlopen(3) and dlclose(3) in
said application to be traced with LTTng-UST (see lttng-ust(3)).
See lttng(1) to learn more about how to control LTTng tracing sessions.
Important
This LTTng-UST helper can also emit shared library load/unload
events (see Shared library load/unload tracking in lttng-ust(3)).
You should NOT use the event records generated by this LTTng-UST
helper (prefixed with lttng_ust_dl:) to track the loading and
unloading of shared libraries, especially in situations where a
dynamically loaded library loads its own dependencies. Instead, do
preload liblttng-ust-dl.so, but use the shared library load/unload
event records, which are more reliable, for your tracking analysis.
The following LTTng-UST events are available when using this library.
lttng_ust_dl:dlopen
Emitted when dlopen(3) is called.
Fields:
┌───────────────┬────────────────────────────┐
│Field name │ Description │
├───────────────┼────────────────────────────┤
│baddr │ Base address of loaded │
│ │ library. │
├───────────────┼────────────────────────────┤
│memsz │ Size of loaded library in │
│ │ memory. │
├───────────────┼────────────────────────────┤
│flags │ Flags passed to dlopen(3). │
├───────────────┼────────────────────────────┤
│path │ Path to loaded library │
│ │ file. │
├───────────────┼────────────────────────────┤
│has_build_id │ Whether or not the loaded │
│ │ library has a build ID. If │
│ │ this field is 1, you can │
│ │ expect that an │
│ │ lttng_ust_dl:build_id │
│ │ event record follows this │
│ │ one (not necessarily │
│ │ immediately after). │
├───────────────┼────────────────────────────┤
│has_debug_link │ Whether or not the loaded │
│ │ library has debug link │
│ │ information. If this field │
│ │ is 1, you can expect that │
│ │ an lttng_ust_dl:debug_link │
│ │ event record follows this │
│ │ one (not necessarily │
│ │ immediately after). │
└───────────────┴────────────────────────────┘
lttng_ust_dl:dlmopen
Emitted when dlmopen(3) is called.
Fields:
┌───────────────┬────────────────────────────┐
│Field name │ Description │
├───────────────┼────────────────────────────┤
│baddr │ Base address of loaded │
│ │ library. │
├───────────────┼────────────────────────────┤
│memsz │ Size of loaded library in │
│ │ memory. │
├───────────────┼────────────────────────────┤
│nsid │ ID of the namespace in │
│ │ which the library is │
│ │ loaded (as passed to │
│ │ dlmopen(3)). │
├───────────────┼────────────────────────────┤
│flags │ Flags passed to │
│ │ dlmopen(3). │
├───────────────┼────────────────────────────┤
│path │ Path to loaded library │
│ │ file. │
├───────────────┼────────────────────────────┤
│has_build_id │ Whether or not the loaded │
│ │ library has a build ID. If │
│ │ this field is 1, you can │
│ │ expect that an │
│ │ lttng_ust_dl:build_id │
│ │ event record follows this │
│ │ one (not necessarily │
│ │ immediately after). │
├───────────────┼────────────────────────────┤
│has_debug_link │ Whether or not the loaded │
│ │ library has debug link │
│ │ information. If this field │
│ │ is 1, you can expect that │
│ │ an lttng_ust_dl:debug_link │
│ │ event record follows this │
│ │ one (not necessarily │
│ │ immediately after). │
└───────────────┴────────────────────────────┘
lttng_ust_dl:dlclose
Emitted when dlclose(3) is called.
Fields:
┌───────────┬────────────────────────┐
│Field name │ Description │
├───────────┼────────────────────────┤
│baddr │ Base address of loaded │
│ │ library. │
└───────────┴────────────────────────┘
lttng_ust_dl:debug_link
Emitted when debug link information is found when loading a library
with dlopen(3). See Debugging Information in Separate Files
<https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-
Files.html> for more information about debug links.
Fields:
┌───────────┬────────────────────────┐
│Field name │ Description │
├───────────┼────────────────────────┤
│baddr │ Base address of loaded │
│ │ library. │
├───────────┼────────────────────────┤
│filename │ Debug link file name. │
├───────────┼────────────────────────┤
│crc │ Debug link file’s CRC. │
└───────────┴────────────────────────┘
lttng_ust_dl:build_id
Emitted when a build ID is found when loading a library with
dlopen(3). See Debugging Information in Separate Files
<https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-
Files.html> for more information about build IDs.
Fields:
┌───────────┬────────────────────────┐
│Field name │ Description │
├───────────┼────────────────────────┤
│baddr │ Base address of loaded │
│ │ library. │
├───────────┼────────────────────────┤
│build_id │ Build ID. │
└───────────┴────────────────────────┘
BUGS
If you encounter any issue or usability problem, please report it on
the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-ust>.
RESOURCES
• 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
COPYRIGHTS
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 for more details.
THANKS
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.
AUTHORS
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>.
SEE ALSO
lttng-ust(3), dlopen(3), lttng(1)
LTTng 2.13.5 09/30/2022 LTTNG-UST-DL(3)
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