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| <h5 class="subsubsection">3.2.3.1 How to install the tracing functionality</h5> |
| |
| <!-- mcheck.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: void <b>mtrace</b> (<var>void</var>)<var><a name="index-mtrace-298"></a></var><br> |
| <blockquote><p>When the <code>mtrace</code> function is called it looks for an environment |
| variable named <code>MALLOC_TRACE</code>. This variable is supposed to |
| contain a valid file name. The user must have write access. If the |
| file already exists it is truncated. If the environment variable is not |
| set or it does not name a valid file which can be opened for writing |
| nothing is done. The behavior of <code>malloc</code> etc. is not changed. |
| For obvious reasons this also happens if the application is installed |
| with the SUID or SGID bit set. |
| |
| <p>If the named file is successfully opened, <code>mtrace</code> installs special |
| handlers for the functions <code>malloc</code>, <code>realloc</code>, and |
| <code>free</code> (see <a href="Hooks-for-Malloc.html#Hooks-for-Malloc">Hooks for Malloc</a>). From then on, all uses of these |
| functions are traced and protocolled into the file. There is now of |
| course a speed penalty for all calls to the traced functions so tracing |
| should not be enabled during normal use. |
| |
| <p>This function is a GNU extension and generally not available on other |
| systems. The prototype can be found in <samp><span class="file">mcheck.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- mcheck.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: void <b>muntrace</b> (<var>void</var>)<var><a name="index-muntrace-299"></a></var><br> |
| <blockquote><p>The <code>muntrace</code> function can be called after <code>mtrace</code> was used |
| to enable tracing the <code>malloc</code> calls. If no (successful) call of |
| <code>mtrace</code> was made <code>muntrace</code> does nothing. |
| |
| <p>Otherwise it deinstalls the handlers for <code>malloc</code>, <code>realloc</code>, |
| and <code>free</code> and then closes the protocol file. No calls are |
| protocolled anymore and the program runs again at full speed. |
| |
| <p>This function is a GNU extension and generally not available on other |
| systems. The prototype can be found in <samp><span class="file">mcheck.h</span></samp>. |
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