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copied!<p>A poor man's solution would be to just log every call <code>malloc</code> and <code>free</code>, then comb through the logs and look for pattern.</p> <p><a href="http://unixhelp.ed.ac.uk/CGI/man-cgi?ld" rel="nofollow"><code>ld</code></a> provides an amazing feature that could help here.</p> <blockquote> <p><code>--wrap=symbol</code> </p> <blockquote> <p>Use a wrapper function for symbol. Any undefined reference to symbol will be resolved to "__wrap_symbol". Any undefined reference to "__real_symbol" will be resolved to symbol.</p> <p>This can be used to provide a wrapper for a system function. The wrapper function should be called "__wrap_symbol". If it wishes to call the system function, it should call "__real_symbol".</p> <p>Here is a trivial example:</p> <pre><code>void * __wrap_malloc (size_t c) { printf ("malloc called with %zu\n", c); return __real_malloc (c); } </code></pre> <p>If you link other code with this file using --wrap malloc, then all calls to "malloc" will call the function "__wrap_malloc" instead. The call to "__real_malloc" in "__wrap_malloc" will call the real "malloc" function.</p> <p>You may wish to provide a "__real_malloc" function as well, so that links without the --wrap option will succeed. If you do this, you should not put the definition of "__real_malloc" in the same file as "__wrap_malloc"; if you do, the assembler may resolve the call before the linker has a chance to wrap it to "malloc".</p> </blockquote> </blockquote> <hr> <h3>Update</h3> <p>Just to be clear on how this is useful.</p> <ul> <li>Add a custom file to Upstart's build.</li> </ul> <p>Like this:</p> <pre><code>void*__wrap_malloc( size_t c ) { void *malloced = __real_malloc(c); /* log malloced with its associated backtrace*/ /* something like: <malloced>: <bt-symbol-1>, <bt-symbol-2>, .. */ return malloced } void __wrap_free( void* addr ) { /* log addr with its associated backtrace*/ /* something like: <addr>: <bt-symbol-1>, <bt-symbol-2>, .. */ __real_free(addr); } </code></pre> <ul> <li><p>Recompile upstart with debug symbols (<code>-g</code>) so you can get some nice backtraces. You can still optimize (<code>-O2/-O3</code>) the code if you wish.</p></li> <li><p>Link Upstart with the extra <code>LD_FLAGS</code> <code>--wrap=malloc</code>, <code>--wrap=free</code>.<br> Now anywhere Upstart calls <code>malloc</code> the symbol will be magically resolved to your new symbol <code>__wrap_malloc</code>. Beautifully this is all transparent to the compiled code as it happens at link time.<br> It's like <a href="http://en.wikipedia.org/wiki/Shim_%28computing%29" rel="nofollow">shimming</a> or <a href="http://en.wikipedia.org/wiki/Instrumentation_%28computer_programming%29" rel="nofollow">instrumenting</a> with out any of the mess.</p></li> <li><p>Run the recompiled Upstart as usual until you're sure the leak has occured.</p></li> <li><p>Look through the logs for mismatch <code>malloced</code>s and <code>addr</code>s.</p></li> </ul> <p>A couple of notes:</p> <ul> <li>The <code>--wrap=symbol</code> feature does not work with function names that are actually macros. So watch out for <code>#define malloc nih_malloc</code>. The this is what libnih does you'd need to use <code>--wrap=nih_malloc</code> and <code>__wrap_nih_malloc</code> instead.</li> <li>Use gcc's <a href="http://www.gnu.org/s/libc/manual/html_node/Backtraces.html" rel="nofollow">builtin backtracing</a> features.</li> <li>All of these changes only affect the recompiled Upstart executable. </li> <li>You could dump the logs to an sqlite DB instead with may make it easier to find mismatch mallocs and frees. </li> <li>you can make you log format an SQL insert statement then just insert them into a database post-mortem for further analysis. </li> </ul>

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