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 COPYING <https://github.com/lttng/lttng-ust/blob/v2.15/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)