| LTTNG-UST-DL(3) | LTTng Manual | LTTNG-UST-DL(3) |
lttng-ust-dl - Dynamic linker tracing (LTTng-UST helper)
Launch your application by preloading liblttng-ust-dl.so:
$ LD_PRELOAD=liblttng-ust-dl.so my-app
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.
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
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
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
Fields:
| Field name | Description |
| baddr | Base address of loaded library. |
lttng_ust_dl:debug_link
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
Fields:
| Field name | Description |
| baddr | Base address of loaded library. |
| build_id | Build ID. |
If you encounter any issue or usability problem, please report it on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-ust>.
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 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.
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>.
| 09/30/2022 | LTTng 2.13.5 |