MTRACE
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Index
Return to Main Contents
NAME
mtrace, muntrace - malloc tracing
SYNOPSIS
#include <mcheck.h>
void mtrace(void);
void muntrace(void);
DESCRIPTION
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.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
mtrace(),
muntrace()
| Thread safety | MT-Unsafe
|
CONFORMING TO
These functions are GNU extensions.
NOTES
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).
BUGS
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.
EXAMPLE
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[])
{
int j;
mtrace();
for (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)).
SEE ALSO
mtrace(1),
malloc(3),
malloc_hook(3),
mcheck(3)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- BUGS
-
- EXAMPLE
-
- SEE ALSO
-
- COLOPHON
-
|
|
- Running on 
-
:
: 