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.
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 |
|---|---|
| Base address of loaded library. |
| Size of loaded library in memory. |
| Flags passed to dlopen(3). |
| Path to loaded library file. |
| Whether or not the loaded library has a build ID. If this field is 1,
you can expect that an |
| Whether or not the loaded library has debug link information. If this
field is 1, you can expect that an |
lttng_ust_dl:dlmopen
Emitted when dlmopen(3) is called.
Fields:
| Field name | Description |
|---|---|
| Base address of loaded library. |
| Size of loaded library in memory. |
| ID of the namespace in which the library is loaded (as passed to dlmopen(3)). |
| Flags passed to dlmopen(3). |
| Path to loaded library file. |
| Whether or not the loaded library has a build ID. If this field is 1,
you can expect that an |
| Whether or not the loaded library has debug link information. If this
field is 1, you can expect that an |
lttng_ust_dl:dlclose
Emitted when dlclose(3) is called.
Fields:
| Field name | Description |
|---|---|
| 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 for more information about debug links.
Fields:
| Field name | Description |
|---|---|
| Base address of loaded library. |
| Debug link file name. |
| 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 for more information about build IDs.
Fields:
| Field name | Description |
|---|---|
| Base address of loaded library. |
| Build ID. |
If you encounter any issue or usability problem, please report it on the LTTng bug tracker.
Mailing list for support and
development: lttng-dev@lists.lttng.org
IRC channel: #lttng on irc.oftc.net
This library is part of the LTTng-UST project.
This library is distributed under the
GNU Lesser
General Public License, version 2.1. See the
COPYING file
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 at École Polytechnique de Montréal for the LTTng journey.