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| <h2 class="chapter">3 Executing the Program</h2> |
| |
| <p>Once the program is compiled for profiling, you must run it in order to |
| generate the information that <code>gprof</code> needs. Simply run the program |
| as usual, using the normal arguments, file names, etc. The program should |
| run normally, producing the same output as usual. It will, however, run |
| somewhat slower than normal because of the time spent collecting and |
| writing the profile data. |
| |
| <p>The way you run the program—the arguments and input that you give |
| it—may have a dramatic effect on what the profile information shows. The |
| profile data will describe the parts of the program that were activated for |
| the particular input you use. For example, if the first command you give |
| to your program is to quit, the profile data will show the time used in |
| initialization and in cleanup, but not much else. |
| |
| <p>Your program will write the profile data into a file called <samp><span class="file">gmon.out</span></samp> |
| just before exiting. If there is already a file called <samp><span class="file">gmon.out</span></samp>, |
| its contents are overwritten. There is currently no way to tell the |
| program to write the profile data under a different name, but you can rename |
| the file afterwards if you are concerned that it may be overwritten. |
| |
| <p>In order to write the <samp><span class="file">gmon.out</span></samp> file properly, your program must exit |
| normally: by returning from <code>main</code> or by calling <code>exit</code>. Calling |
| the low-level function <code>_exit</code> does not write the profile data, and |
| neither does abnormal termination due to an unhandled signal. |
| |
| <p>The <samp><span class="file">gmon.out</span></samp> file is written in the program's <em>current working |
| directory</em> at the time it exits. This means that if your program calls |
| <code>chdir</code>, the <samp><span class="file">gmon.out</span></samp> file will be left in the last directory |
| your program <code>chdir</code>'d to. If you don't have permission to write in |
| this directory, the file is not written, and you will get an error message. |
| |
| <p>Older versions of the <span class="sc">gnu</span> profiling library may also write a file |
| called <samp><span class="file">bb.out</span></samp>. This file, if present, contains an human-readable |
| listing of the basic-block execution counts. Unfortunately, the |
| appearance of a human-readable <samp><span class="file">bb.out</span></samp> means the basic-block |
| counts didn't get written into <samp><span class="file">gmon.out</span></samp>. |
| The Perl script <code>bbconv.pl</code>, included with the <code>gprof</code> |
| source distribution, will convert a <samp><span class="file">bb.out</span></samp> file into |
| a format readable by <code>gprof</code>. Invoke it like this: |
| |
| <pre class="smallexample"> bbconv.pl < bb.out > <var>bh-data</var> |
| </pre> |
| <p>This translates the information in <samp><span class="file">bb.out</span></samp> into a form that |
| <code>gprof</code> can understand. But you still need to tell <code>gprof</code> |
| about the existence of this translated information. To do that, include |
| <var>bb-data</var> on the <code>gprof</code> command line, <em>along with |
| </em><samp><span class="file">gmon.out</span></samp>, like this: |
| |
| <pre class="smallexample"> gprof <var>options</var> <var>executable-file</var> gmon.out <var>bb-data</var> [<var>yet-more-profile-data-files</var>...] [> <var>outfile</var>] |
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