NAME
mtrace, muntrace - malloc tracing SYNOPSIS
#include
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 deal‐ location. 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 vari‐ able MALLOCTRACE, which should contain the pathname of a file in which the tracing information is to be recorded. If the pathname is success‐ fully opened, it is truncated to zero length. If MALLOCTRACE 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, MALLOCTRACE 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 com‐
piled with debugging enabled, so that line-number information is recorded in the executable. The tracing performed by mtrace() incurs a performance penalty (if MAL‐ LOCTRACE points to a valid, writable pathname). BUGS
The line-number information produced by mtrace(1) is not always pre‐ cise: the line number references may refer to the previous or following
(non-blank) 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 tmtrace.c
#include
#include
#include
int main(int argc, char *argv[]) { int j; mtrace(); for (j = 0; j < 2; j++) malloc(100); /* Never freeda memory leak */ calloc(16, 16); /* Never freeda memory leak */ exit(EXITSUCCESS); } When we run the program as follows, we see that mtrace() diagnosed mem‐ ory leaks at two different locations in the program: $ cc -g tmtrace.c -o tmtrace
$ export MALLOCTRACE=/tmp/t
$ ./tmtrace
$ mtrace ./tmtrace $MALLOCTRACE Memory not freed:
- Address Size Caller 0x084c9378 0x64 at /home/cecilia/tmtrace.c:12 0x084c93e0 0x64 at /home/cecilia/tmtrace.c:12 0x084c9448 0x100 at /home/cecilia/tmtrace.c:16 The first two messages about unfreed memory correspond to the two mal‐ loc(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), mallochook(3), mcheck(3) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2012-04-18 MTRACE(3)