Manpage of MTRACE
MTRACESection: Linux Programmer's Manual (3)
NAMEmtrace, muntrace - malloc tracing
DESCRIPTIONThe 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_TRACEis 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_TRACEis ignored, and mtrace() has no effect.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
|mtrace(), muntrace()||Thread safety||MT-Unsafe|
CONFORMING TOThese functions are GNU extensions.
NOTESIn 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.
BUGSThe line-number information produced by mtrace(1) is not always precise: the line number references may refer to the or following (nonblank) line of the source code.
EXAMPLEThe 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:
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$ ./t_mtrace$ mtrace ./t_mtrace $MALLOC_TRACEMemory 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
SEE ALSOmtrace(1), malloc(3), malloc_hook(3), mcheck(3)
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