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1 | .\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com> |
2 | .\" | |
3 | .\" Permission is granted to make and distribute verbatim copies of this | |
4 | .\" manual provided the copyright notice and this permission notice are | |
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7 | .\" Permission is granted to copy and distribute modified versions of this | |
8 | .\" manual under the conditions for verbatim copying, provided that the | |
9 | .\" entire resulting derived work is distributed under the terms of a | |
10 | .\" permission notice identical to this one. | |
11 | .\" | |
12 | .\" Since the Linux kernel and libraries are constantly changing, this | |
13 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
14 | .\" responsibility for errors or omissions, or for damages resulting from | |
15 | .\" the use of the information contained herein. The author(s) may not | |
16 | .\" have taken the same level of care in the production of this manual, | |
17 | .\" which is licensed free of charge, as they might when working | |
18 | .\" professionally. | |
19 | .\" | |
20 | .\" Formatted or processed versions of this manual, if unaccompanied by | |
21 | .\" the source, must acknowledge the copyright and authors of this work. | |
22 | .\" | |
361c3c7f | 23 | .TH MTRACE 3 2012-04-18 "GNU" "Linux Programmer's Manual" |
fea681da | 24 | .SH NAME |
c196e485 | 25 | mtrace, muntrace \- malloc tracing |
fea681da | 26 | .SH SYNOPSIS |
fea681da MK |
27 | .B "#include <mcheck.h>" |
28 | .sp | |
29 | .B "void mtrace(void);" | |
30 | .sp | |
31 | .B "void muntrace(void);" | |
32 | .SH DESCRIPTION | |
c196e485 | 33 | The |
fea681da | 34 | .BR mtrace () |
c196e485 MK |
35 | function installs hook functions for the memory-allocation functions |
36 | .RB ( malloc (3), | |
fb186734 | 37 | .BR realloc (3) |
c196e485 MK |
38 | .BR memalign (3), |
39 | .BR free (3)). | |
40 | These hook functions record tracing information about memory allocation | |
41 | and deallocation. | |
42 | The tracing information can be used to discover memory leaks and | |
43 | attempts to free nonallocated memory in a program. | |
44 | ||
45 | The | |
fea681da | 46 | .BR muntrace () |
c196e485 MK |
47 | function disables the hook functions installed by |
48 | .BR mtrace (), | |
49 | so that tracing information is no longer recorded | |
50 | for the memory-allocation functions. | |
51 | If no hook functions were successfully installed by | |
52 | .BR mtrace (), | |
53 | .BR muntrace () | |
54 | does nothing. | |
55 | ||
56 | When | |
eace9488 | 57 | .BR mtrace () |
c196e485 MK |
58 | is called, it checks the value of the environment variable |
59 | .BR MALLOC_TRACE , | |
60 | which should contain the pathname of a file in which | |
61 | the tracing information is to be recorded. | |
62 | If the pathname is successfully opened, it is truncated to zero length. | |
63 | ||
64 | If | |
65 | .BR MALLOC_TRACE | |
66 | is not set, | |
67 | or the pathname it specifies is invalid or not writable, | |
68 | then no hook functions are installed, and | |
fea681da | 69 | .BR mtrace () |
c196e485 MK |
70 | has no effect. |
71 | In set-user-ID and set-group-ID programs, | |
72 | .BR MALLOC_TRACE | |
73 | is ignored, and | |
fea681da | 74 | .BR mtrace () |
c196e485 | 75 | has no effect. |
2b2581ee | 76 | .SH "CONFORMING TO" |
c196e485 | 77 | These functions are GNU extensions. |
19c98696 | 78 | .SH NOTES |
c196e485 MK |
79 | In normal usage, |
80 | .BR mtrace () | |
81 | is called once at the start of execution of a program, and | |
82 | .BR muntrace () | |
83 | is never called. | |
84 | ||
85 | The tracing output produced after a call to | |
86 | .BR mtrace () | |
87 | is textual, but not designed to be human readable. | |
88 | The GNU C library provides a Perl script, | |
89 | .BR mtrace (1), | |
90 | that interprets the trace log and produces human-readable output. | |
91 | For best results, | |
92 | the traced program should be compiled with debugging enabled, | |
93 | so that line-number information is recorded in the executable. | |
94 | ||
95 | The tracing performed by | |
96 | .BR mtrace () | |
97 | incurs a performance penalty (if | |
98 | .B MALLOC_TRACE | |
99 | points to a valid, writable pathname). | |
100 | .SH BUGS | |
101 | The line-number information produced by | |
102 | .BR mtrace (1) | |
103 | is not always precise: | |
104 | the line number references may refer to the previous or following (non-blank) | |
105 | line of the source code. | |
106 | .SH EXAMPLE | |
107 | The shell session below demonstrates the use of the | |
108 | .BR mtrace () | |
109 | function and the | |
110 | .BR mtrace (1) | |
111 | command in a program that has memory leaks at two different locations. | |
112 | The demonstration uses the following program: | |
113 | .in +4 | |
114 | .nf | |
115 | ||
116 | .RB "$ " "cat t_mtrace.c" | |
117 | #include <mcheck.h> | |
118 | #include <stdlib.h> | |
119 | #include <stdio.h> | |
120 | ||
121 | int | |
122 | main(int argc, char *argv[]) | |
123 | { | |
124 | int j; | |
125 | ||
126 | mtrace(); | |
127 | ||
128 | for (j = 0; j < 2; j++) | |
129 | malloc(100); /* Never freed\-\-a memory leak */ | |
130 | ||
131 | calloc(16, 16); /* Never freed\-\-a memory leak */ | |
132 | exit(EXIT_SUCCESS); | |
133 | } | |
134 | ||
135 | .fi | |
136 | .in | |
137 | When we run the program as follows, we see that | |
fea681da | 138 | .BR mtrace () |
c196e485 MK |
139 | diagnosed memory leaks at two different locations in the program: |
140 | .in +4n | |
141 | .nf | |
142 | ||
143 | .RB "$ " "cc \-g t_mtrace.c \-o t_mtrace" | |
144 | .RB "$ " "export MALLOC_TRACE=/tmp/t" | |
145 | .RB "$ " "./t_mtrace" | |
146 | .RB "$ " "mtrace ./t_mtrace $MALLOC_TRACE" | |
147 | Memory not freed: | |
148 | ----------------- | |
149 | Address Size Caller | |
150 | 0x084c9378 0x64 at /home/cecilia/t_mtrace.c:12 | |
151 | 0x084c93e0 0x64 at /home/cecilia/t_mtrace.c:12 | |
152 | 0x084c9448 0x100 at /home/cecilia/t_mtrace.c:16 | |
153 | .fi | |
154 | .in | |
155 | ||
156 | The first two messages about unfreed memory correspond to the two | |
157 | .BR malloc (3) | |
158 | calls inside the | |
159 | .I for | |
160 | loop. | |
161 | The final message corresponds to the call to | |
162 | .BR calloc (3) | |
163 | (which in turn calls | |
164 | .BR malloc (3)). | |
fea681da | 165 | .SH "SEE ALSO" |
c196e485 | 166 | .BR mtrace (1), |
fea681da | 167 | .BR malloc (3), |
361c3c7f MK |
168 | .BR malloc_hook (3), |
169 | .BR mcheck (3) |