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