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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 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 Ecole Polytechnique de Montreal 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)
NAME | SYNOPSIS | DESCRIPTION | BUGS | RESOURCES | COPYRIGHTS | THANKS | AUTHORS | SEE ALSO
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