Provided by: liblttng-ust-dev_2.13.9-1_amd64 
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 COPYING
<https://github.com/lttng/lttng-ust/blob/v2.13/COPYING> file 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 2.13.9 04/14/2025 LTTNG-UST-DL(3)