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MTRACE
Section: Linux user manual (1)Updated: 2017-09-15
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NAME
mtrace - interpret the malloc trace logSYNOPSIS
mtrace [option]... [binary] mtracedataDESCRIPTION
mtrace is a Perl script used to interpret and provide human readable output of the trace log contained in the file mtracedata, whose contents were produced by mtrace(3). If binary is provided, the output of mtrace also contains the source file name with line number information for problem locations (assuming that binary was compiled with debugging information).For more information about the mtrace(3) function and mtrace script usage, see mtrace(3).
OPTIONS
- --help
- Print help and exit.
- --version
- Print version information and exit.
BUGS
For bug reporting instructions, please see:SEE ALSO
memusage(1), mtrace(3)COLOPHON
This page is part of release 4.15 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/.
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Time: 04:45:26 GMT, September 16, 2022 Content-type: text/html; charset=UTF-8
MTRACE
Section: Linux Programmer's Manual (3)Updated: 2017-09-15
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NAME
mtrace, muntrace - malloc tracingSYNOPSIS
#include <mcheck.h>void mtrace(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 4.15 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/.
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This document was created by man2html, using the manual pages.
Time: 04:45:45 GMT, September 16, 2022
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