<title>Debugging Memory Allocation in APR - Apache HTTP Server</title>
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3</a> > <a href="./">Developer Documentation</a></div><div id="page-content"><div id="preamble"><h1>Debugging Memory Allocation in APR</h1>
+<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.
5</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 mechanisms 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>
+ <p>
+ This document has been removed.
+ </p>
+</div>
</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 <code>alloc.c</code>
- 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>
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