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25 .TH MTRACE 3 2012-04-18 "GNU" "Linux Programmer's Manual"
27 mtrace, muntrace \- malloc tracing
29 .B "#include <mcheck.h>"
31 .B "void mtrace(void);"
33 .B "void muntrace(void);"
37 function installs hook functions for the memory-allocation functions
42 These hook functions record tracing information about memory allocation
44 The tracing information can be used to discover memory leaks and
45 attempts to free nonallocated memory in a program.
49 function disables the hook functions installed by
51 so that tracing information is no longer recorded
52 for the memory-allocation functions.
53 If no hook functions were successfully installed by
60 is called, it checks the value of the environment variable
62 which should contain the pathname of a file in which
63 the tracing information is to be recorded.
64 If the pathname is successfully opened, it is truncated to zero length.
69 or the pathname it specifies is invalid or not writable,
70 then no hook functions are installed, and
73 In set-user-ID and set-group-ID programs,
79 These functions are GNU extensions.
83 is called once at the start of execution of a program, and
87 The tracing output produced after a call to
89 is textual, but not designed to be human readable.
90 The GNU C library provides a Perl script,
92 that interprets the trace log and produces human-readable output.
94 the traced program should be compiled with debugging enabled,
95 so that line-number information is recorded in the executable.
97 The tracing performed by
99 incurs a performance penalty (if
101 points to a valid, writable pathname).
103 The line-number information produced by
105 is not always precise:
106 the line number references may refer to the previous or following (non-blank)
107 line of the source code.
109 The shell session below demonstrates the use of the
113 command in a program that has memory leaks at two different locations.
114 The demonstration uses the following program:
118 .RB "$ " "cat t_mtrace.c"
124 main(int argc, char *argv[])
130 for (j = 0; j < 2; j++)
131 malloc(100); /* Never freed\-\-a memory leak */
133 calloc(16, 16); /* Never freed\-\-a memory leak */
139 When we run the program as follows, we see that
141 diagnosed memory leaks at two different locations in the program:
145 .RB "$ " "cc \-g t_mtrace.c \-o t_mtrace"
146 .RB "$ " "export MALLOC_TRACE=/tmp/t"
147 .RB "$ " "./t_mtrace"
148 .RB "$ " "mtrace ./t_mtrace $MALLOC_TRACE"
152 0x084c9378 0x64 at /home/cecilia/t_mtrace.c:12
153 0x084c93e0 0x64 at /home/cecilia/t_mtrace.c:12
154 0x084c9448 0x100 at /home/cecilia/t_mtrace.c:16
158 The first two messages about unfreed memory correspond to the two
163 The final message corresponds to the call to