mtrace, muntrace — malloc tracing
#include <mcheck.h>
void
mtrace( |
void); |
void
muntrace( |
void); |
The mtrace() function
installs hook functions for the memory-allocation functions
(malloc(3), realloc(3) memalign(3), free(3)). These hook
functions record tracing information about memory allocation
and deallocation. The tracing information can be used to
discover memory leaks and attempts to free nonallocated
memory in a program.
The muntrace() function
disables the hook functions installed by mtrace(), so that tracing information is no
longer recorded for the memory-allocation functions. If no
hook functions were successfully installed by mtrace(), muntrace() does nothing.
When mtrace() is called, it
checks the value of the environment variable MALLOC_TRACE, 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.
If MALLOC_TRACE is not set,
or the pathname it specifies is invalid or not writable, then
no hook functions are installed, and mtrace() has no effect. In set-user-ID and
set-group-ID programs, MALLOC_TRACE is ignored, and mtrace() has no effect.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
mtrace(), muntrace() |
Thread safety | MT-Unsafe |
In normal usage, mtrace() is
called once at the start of execution of a program, and
muntrace() is never called.
The tracing output produced after a call to mtrace() is textual, but not designed to be
human readable. The GNU C library provides a Perl script,
mtrace(1), 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 mtrace() incurs a performance penalty (if
MALLOC_TRACE points to a valid,
writable pathname).
The line-number information produced by mtrace(1) 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
mtrace() function and the
mtrace(1) command in a program
that has memory leaks at two different locations. The
demonstration uses the following program:
$cat t_mtrace.c#include <mcheck.h> #include <stdlib.h> #include <stdio.h> int main(int argc, char *argv[]) { mtrace(); for (int j = 0; j < 2; j++) malloc(100); /* Never freed−−a memory leak */ calloc(16, 16); /* Never freed−−a memory leak */ exit(EXIT_SUCCESS); }
When we run the program as follows, we see that
mtrace() diagnosed memory leaks
at two different locations in the program:
$ cc −g t_mtrace.c −o t_mtrace $ export MALLOC_TRACE=/tmp/t $./t_mtrace$ 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 malloc(3) calls inside the
for loop. The final message
corresponds to the call to calloc(3) (which in turn
calls malloc(3)).
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright (c) 2012 by Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |