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 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)