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Linux Programmer's Manual (3)
mtrace, muntrace - malloc tracing
function installs hook functions for the memory-allocation functions
These hook functions record tracing information about memory allocation
The tracing information can be used to discover memory leaks and
attempts to free nonallocated memory in a program.
function disables the hook functions installed by
so that tracing information is no longer recorded
for the memory-allocation functions.
If no hook functions were successfully installed by
is called, it checks the value of the environment variable
which should contain the pathname of a file in which
the tracing information is to be recorded.
If the pathname is successfully opened, it is truncated to zero length.
is not set,
or the pathname it specifies is invalid or not writable,
then no hook functions are installed, and
has no effect.
In set-user-ID and set-group-ID programs,
is ignored, and
has no effect.
These functions are GNU extensions.
In normal usage,
is called once at the start of execution of a program, and
is never called.
The tracing output produced after a call to
is textual, but not designed to be human readable.
The GNU C library provides a Perl script,
that interprets the trace log and produces human-readable output.
For best results,
the traced program should be compiled with debugging enabled,
so that line-number information is recorded in the executable.
The tracing performed by
incurs a performance penalty (if
points to a valid, writable pathname).
The line-number information produced by
is not always precise:
the line number references may refer to the previous or following (nonblank)
line of the source code.
The shell session below demonstrates the use of the
function and the
command in a program that has memory leaks at two different locations.
The demonstration uses the following program:
$ cat t_mtrace.c
main(int argc, char *argv)
for (j = 0; j < 2; j++)
malloc(100); /* Never freed--a memory leak */
calloc(16, 16); /* Never freed--a memory leak */
When we run the program as follows, we see that
diagnosed memory leaks at two different locations in the program:
$ cc -g t_mtrace.c -o t_mtrace
$ export MALLOC_TRACE=/tmp/t
$ mtrace ./t_mtrace $MALLOC_TRACE
Memory not freed:
Address Size Caller
0x084c9378 0x64 at /home/cecilia/t_mtrace.c:12
0x084c93e0 0x64 at /home/cecilia/t_mtrace.c:12
0x084c9448 0x100 at /home/cecilia/t_mtrace.c:16
The first two messages about unfreed memory correspond to the two
calls inside the
The final message corresponds to the call to
(which in turn calls
This page is part of release 3.66 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
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This document was created by
using the manual pages.
Time: 21:43:01 GMT, July 12, 2014