mtrace, muntrace - malloc tracing
() function installs hook functions for the memory-allocation
(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.
() 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
() does nothing.
() 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 mtrace
() has no
effect. In set-user-ID and set-group-ID programs, MALLOC_TRACE
ignored, and mtrace
() has no effect.
For an explanation of the terms used in this section, see attributes
|mtrace (), muntrace ()
These functions are GNU extensions.
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,
(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
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
(1) 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 mtrace
() 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
(3) calls inside the for
loop. The final message
corresponds to the call to calloc
(3) (which in turn calls