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25 .TH MTRACE 3 2021-03-22 "GNU" "Linux Programmer's Manual"
27 mtrace, muntrace \- malloc tracing
30 .B "#include <mcheck.h>"
32 .B "void mtrace(void);"
33 .B "void muntrace(void);"
38 function installs hook functions for the memory-allocation functions
43 These hook functions record tracing information about memory allocation
45 The tracing information can be used to discover memory leaks and
46 attempts to free nonallocated memory in a program.
50 function disables the hook functions installed by
52 so that tracing information is no longer recorded
53 for the memory-allocation functions.
54 If no hook functions were successfully installed by
61 is called, it checks the value of the environment variable
63 which should contain the pathname of a file in which
64 the tracing information is to be recorded.
65 If the pathname is successfully opened, it is truncated to zero length.
70 or the pathname it specifies is invalid or not writable,
71 then no hook functions are installed, and
74 In set-user-ID and set-group-ID programs,
80 For an explanation of the terms used in this section, see
88 Interface Attribute Value
92 T} Thread safety MT-Unsafe
97 .\" FIXME: The marking is different from that in the glibc manual,
98 .\" markings in glibc manual are more detailed:
100 .\" mtrace: MT-Unsafe env race:mtrace const:malloc_hooks init
101 .\" muntrace: MT-Unsafe race:mtrace const:malloc_hooks locale
103 .\" But there is something wrong in glibc manual, for example:
104 .\" glibc manual says muntrace should have marking locale because it calls
105 .\" fprintf(), but muntrace does not execute area which cause locale problem.
107 These functions are GNU extensions.
111 is called once at the start of execution of a program, and
115 The tracing output produced after a call to
117 is textual, but not designed to be human readable.
118 The GNU C library provides a Perl script,
120 that interprets the trace log and produces human-readable output.
122 the traced program should be compiled with debugging enabled,
123 so that line-number information is recorded in the executable.
125 The tracing performed by
127 incurs a performance penalty (if
129 points to a valid, writable pathname).
131 The line-number information produced by
133 is not always precise:
134 the line number references may refer to the previous or following (nonblank)
135 line of the source code.
137 The shell session below demonstrates the use of the
141 command in a program that has memory leaks at two different locations.
142 The demonstration uses the following program:
146 .RB "$ " "cat t_mtrace.c"
152 main(int argc, char *argv[])
156 for (int j = 0; j < 2; j++)
157 malloc(100); /* Never freed\-\-a memory leak */
159 calloc(16, 16); /* Never freed\-\-a memory leak */
165 When we run the program as follows, we see that
167 diagnosed memory leaks at two different locations in the program:
171 .RB "$ " "cc \-g t_mtrace.c \-o t_mtrace"
172 .RB "$ " "export MALLOC_TRACE=/tmp/t"
173 .RB "$ " "./t_mtrace"
174 .RB "$ " "mtrace ./t_mtrace $MALLOC_TRACE"
176 -\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
178 0x084c9378 0x64 at /home/cecilia/t_mtrace.c:12
179 0x084c93e0 0x64 at /home/cecilia/t_mtrace.c:12
180 0x084c9448 0x100 at /home/cecilia/t_mtrace.c:16
184 The first two messages about unfreed memory correspond to the two
189 The final message corresponds to the call to