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POPOSIX: How do you determine your own process's file image so you can exec yourself?
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  1. POPOSIX: How do you determine your own process's file image so you can exec yourself?
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    copied!<p>How does one determine the file that represents the current process' executable?</p> <p>The problem is that <code>argv[0]</code> is not reliable, as if it was called via <code>execXp</code>, the path entry that satisfied a non-qualified command may or may not be prepended. Furthermore, ANY caller to <code>exec*</code> can replace <code>argv[0]</code> with ANYTHING.</p> <p>Hence, if you run <code>ps</code>, you are not guaranteed that <code>argv[0]</code> will be <code>"/usr/bin/ps"</code>. In fact, you're probably guaranteed the OPPOSITE.</p> <p>I need one of the following:</p> <ol> <li>the full path name (without doing a path search myself, lest the envp I am using is not the one the shell used)</li> <li>a live, pre-opened file descriptor to the file that corresponds to the current process' image</li> <li>some magic descriptor that corresponds to the code segment currently in memory (not quite sure about the BSS segment, though)</li> </ol> <p>In this way, at startup I can quickly open an FD to my own executable (for case 1., in case the file gets removed and becomes unopenable), and then at a much later date call:</p> <pre><code>int fexecve(int fd, char *const argv[], char *const envp[]); </code></pre> <p>to <code>fork</code>/<code>exec</code> myself (typically needed on OS-X to work around the unreliability of the global and system descriptor state after <code>fork()</code> ). In other words (this example is silly, of course):</p> <pre><code>void magicallyReplicate(argc, argv) { if (!fork()) { magicallyExecMyself(argc, argv); } } </code></pre> <p>or even just:</p> <pre><code>void startOver(argc, argv) { magicallyExecMyself(argc, argv); } </code></pre> <p>Of course, in my example, I will be using different <code>argv</code>'s so that I can run in a different mode.</p> <p>(early "no" retort: you can't use <code>clone()</code>, as it is of <code>fork()</code>'s lineage)</p>
 

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