contents/using-lttng/instrumenting/prebuilt-ust-helpers/liblttng-ust-dl.md

   1 ---
   2 id: liblttng-ust-dl
   3 since: 2.4
   4 ---
   5
   6 This LTTng-UST helper causes all calls to `dlopen()` and `dlclose()`
   7 in the target application to be traced with LTTng.
   8
   9 The helper's shared object, `liblttng-ust-dl.so`, registers the
  10 following tracepoints when preloaded:
  11
  12 <div class="table">
  13 <table class="func-desc">
  14     <thead>
  15         <tr>
  16             <th><abbr title="Tracepoint">TP</abbr> provider name</th>
  17             <th><abbr title="Tracepoint">TP</abbr> name</th>
  18             <th>Description/fields</th>
  19         </tr>
  20     </thead>
  21     <tbody>
  22         <tr>
  23             <td rowspan="2">
  24                 <code class="no-bg">lttng_ust_dl</code>
  25             </td>
  26             <td>
  27                 <code class="no-bg">dlopen</code>
  28             </td>
  29             <td>
  30                 <p><code>dlopen()</code> call</p>
  31
  32                 <ul>
  33                     <li>
  34                         <code class="arg">baddr</code>&nbsp;memory
  35                         base address
  36                         (where the dynamic linker placed the shared
  37                         object)
  38                     </li>
  39                     <li>
  40                         <code class="arg">sopath</code>&nbsp;file system
  41                         path to the loaded shared object
  42                     </li>
  43                     <li>
  44                         <code class="arg">size</code>&nbsp;file size
  45                         of the the loaded shared object
  46                     </li>
  47                     <li>
  48                         <code class="arg">mtime</code>&nbsp;last
  49                         modification time (seconds since Epoch time)
  50                         of the loaded shared object
  51                     </li>
  52                 </ul>
  53             </td>
  54         </tr>
  55         <tr>
  56             <td>
  57                 <code class="no-bg">dlclose</code>
  58             </td>
  59             <td>
  60                 <p><code>dlclose()</code> call</p>
  61
  62                 <ul>
  63                     <li>
  64                         <code class="arg">baddr</code>&nbsp;memory
  65                         base address
  66                     </li>
  67                 </ul>
  68             </td>
  69         </tr>
  70     </tbody>
  71 </table>
  72 </div>
  73
  74 To use this LTTng-UST helper with any user application, independently of
  75 how the latter is built, do:
  76
  77 <pre class="term">
  78 LD_PRELOAD=liblttng-ust-dl.so my-app
  79 </pre>
  80
  81 Of course, like any other tracepoint, the ones above need to be enabled
  82 in order for LTTng-UST to generate events. This is done using the
  83 `lttng` command line tool
  84 (see [Controlling tracing](#doc-controlling-tracing)).