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

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