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>.