blob: 1e2186983f6ad882503bc20e65a8d90217c250fa (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
|
<?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 2.2</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/">Documentation</a> > <a href="../">Version 2.2</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>
</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>
</div><div id="footer">
<p class="apache">Copyright 2011 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>
|
