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<?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX This file is generated from xml source: DO NOT EDIT XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX --> <title>Debugging Memory Allocation in APR - Apache HTTP Server</title> <link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> <link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> <link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /> <link href="../images/favicon.ico" rel="shortcut icon" /></head> <body id="manual-page"><div id="page-header"> <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> <p class="apache">Apache HTTP Server Version 2.0</p> <img alt="" src="../images/feather.gif" /></div> <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> <div id="path"> <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Developer Documentation</a></div><div id="page-content"><div id="preamble"><h1>Debugging Memory Allocation in APR</h1> <div class="toplang"> <p><span>Available Languages: </span><a href="../en/developer/debugging.html" title="English"> en </a></p> </div> <p>The allocation mechanism's within APR have a number of debugging modes that can be used to assist in finding memory problems. This document describes the modes available and gives instructions on activating them.</p> </div> <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#options">Available debugging options</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#combo">Allowable Combinations</a></li> <li><img alt="" src="../images/down.gif" /> <a href="#howto">Activating Debugging Options</a></li> </ul></div> <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="options" id="options">Available debugging options</a></h2> <h3><a name="alloc_debug" id="alloc_debug">Allocation Debugging - ALLOC_DEBUG</a></h3> <div class="note">Debugging support: Define this to enable code which helps detect re-use of <code>free()</code>d memory and other such nonsense.</div> <p>The theory is simple. The <code>FILL_BYTE</code> (<code>0xa5</code>) is written over all <code>malloc</code>'d memory as we receive it, and is written over everything that we free up during a <code>clear_pool</code>. We check that blocks on the free list always have the <code>FILL_BYTE</code> in them, and we check during <code>palloc()</code> that the bytes still have <code>FILL_BYTE</code> in them. If you ever see garbage URLs or whatnot containing lots of <code>0xa5</code>s then you know something used data that's been freed or uninitialized.</p> <h3><a name="alloc_use_malloc" id="alloc_use_malloc">Malloc Support - ALLOC_USE_MALLOC</a></h3> <div class="note">If defined all allocations will be done with <code>malloc()</code> and <code>free()</code>d appropriately at the end.</div> <p>This is intended to be used with something like Electric Fence or Purify to help detect memory problems. Note that if you're using efence then you should also add in <code>ALLOC_DEBUG</code>. But don't add in <code>ALLOC_DEBUG</code> if you're using Purify because <code>ALLOC_DEBUG</code> would hide all the uninitialized read errors that Purify can diagnose.</p> <h3><a name="pool_debug" id="pool_debug">Pool Debugging - POOL_DEBUG</a></h3> <div class="note">This is intended to detect cases where the wrong pool is used when assigning data to an object in another pool.</div> <p>In particular, it causes the <code>table_{set,add,merge}n</code> routines to check that their arguments are safe for the <code>apr_table_t</code> they're being placed in. It currently only works with the unix multiprocess model, but could be extended to others.</p> <h3><a name="make_table_profile" id="make_table_profile">Table Debugging - MAKE_TABLE_PROFILE</a></h3> <div class="note">Provide diagnostic information about make_table() calls which are possibly too small.</div> <p>This requires a recent gcc which supports <code>__builtin_return_address()</code>. The error_log output will be a message such as:</p> <div class="example"><p><code> table_push: apr_table_t created by 0x804d874 hit limit of 10 </code></p></div> <p>Use <code>l *0x804d874</code> to find the source that corresponds to. It indicates that a <code>apr_table_t</code> allocated by a call at that address has possibly too small an initial <code>apr_table_t</code> size guess.</p> <h3><a name="alloc_stats" id="alloc_stats">Allocation Statistics - ALLOC_STATS</a></h3> <div class="note">Provide some statistics on the cost of allocations.</div> <p>This requires a bit of an understanding of how alloc.c works.</p> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="combo" id="combo">Allowable Combinations</a></h2> <p>Not all the options outlined above can be activated at the same time. the following table gives more information.</p> <table class="bordered"><tr class="header"><th /> <th>ALLOC DEBUG</th> <th>ALLOC USE MALLOC</th> <th>POOL DEBUG</th> <th>MAKE TABLE PROFILE</th> <th>ALLOC STATS</th></tr> <tr><th>ALLOC DEBUG</th> <td>-</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td></tr> <tr class="odd"><th>ALLOC USE MALLOC</th> <td>No</td><td>-</td><td>No</td><td>No</td><td>No</td></tr> <tr><th>POOL DEBUG</th> <td>Yes</td><td>No</td><td>-</td><td>Yes</td><td>Yes</td></tr> <tr class="odd"><th>MAKE TABLE PROFILE</th> <td>Yes</td><td>No</td><td>Yes</td><td>-</td><td>Yes</td></tr> <tr><th>ALLOC STATS</th> <td>Yes</td><td>No</td><td>Yes</td><td>Yes</td><td>-</td></tr> </table> <p>Additionally the debugging options are not suitable for multi-threaded versions of the server. When trying to debug with these options the server should be started in single process mode.</p> </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> <div class="section"> <h2><a name="howto" id="howto">Activating Debugging Options</a></h2> <p>The various options for debugging memory are now enabled in the <code>apr_general.h</code> header file in APR. The various options are enabled by uncommenting the define for the option you wish to use. The section of the code currently looks like this (<em>contained in srclib/apr/include/apr_pools.h</em>)</p> <div class="example"><p><code> /*<br /> #define ALLOC_DEBUG<br /> #define POOL_DEBUG<br /> #define ALLOC_USE_MALLOC<br /> #define MAKE_TABLE_PROFILE<br /> #define ALLOC_STATS<br /> */<br /> <br /> typedef struct ap_pool_t {<br /> <span class="indent"> union block_hdr *first;<br /> union block_hdr *last;<br /> struct cleanup *cleanups;<br /> struct process_chain *subprocesses;<br /> struct ap_pool_t *sub_pools;<br /> struct ap_pool_t *sub_next;<br /> struct ap_pool_t *sub_prev;<br /> struct ap_pool_t *parent;<br /> char *free_first_avail;<br /> </span> #ifdef ALLOC_USE_MALLOC<br /> <span class="indent"> void *allocation_list;<br /> </span> #endif<br /> #ifdef POOL_DEBUG<br /> <span class="indent"> struct ap_pool_t *joined;<br /> </span> #endif<br /> <span class="indent"> int (*apr_abort)(int retcode);<br /> struct datastruct *prog_data;<br /> </span> } ap_pool_t; </code></p></div> <p>To enable allocation debugging simply move the <code>#define ALLOC_DEBUG</code> above the start of the comments block and rebuild the server.</p> <div class="note"><h3>Note</h3> <p>In order to use the various options the server <strong>must</strong> be rebuilt after editing the header file.</p> </div> </div></div> <div class="bottomlang"> <p><span>Available Languages: </span><a href="../en/developer/debugging.html" title="English"> en </a></p> </div><div id="footer"> <p class="apache">Copyright 1999-2004 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div> </body></html> 
