x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
MCHECK(3) Linux Programmer's Manual MCHECK(3)
NAME
mcheck, mcheck_check_all, mcheck_pedantic, mprobe - heap consistency
checking
SYNOPSIS
#include <mcheck.h>
int mcheck(void (*abortfunc)(enum mcheck_status mstatus));
int mcheck_pedantic(void (*abortfunc)(enum mcheck_status mstatus));
void mcheck_check_all(void);
enum mcheck_status mprobe(void *ptr);
DESCRIPTION
The mcheck() function installs a set of debugging hooks for the mal-
loc(3) family of memory-allocation functions. These hooks cause cer-
tain consistency checks to be performed on the state of the heap. The
checks can detect application errors such as freeing a block of memory
more than once or corrupting the bookkeeping data structures that imme-
diately precede a block of allocated memory.
To be effective, the mcheck() function must be called before the first
call to malloc(3) or a related function. In cases where this is diffi-
cult to ensure, linking the program with -lmcheck inserts an implicit
call to mcheck() (with a NULL argument) before the first call to a mem-
ory-allocation function.
The mcheck_pedantic() function is similar to mcheck(), but performs
checks on all allocated blocks whenever one of the memory-allocation
functions is called. This can be very slow!
The mcheck_check_all() function causes an immediate check on all allo-
cated blocks. This call is effective only if mcheck() is called
beforehand.
If the system detects an inconsistency in the heap, the caller-supplied
function pointed to by abortfunc is invoked with a single argument
argument, mstatus, that indicates what type of inconsistency was
detected. If abortfunc is NULL, a default function prints an error
message on stderr and calls abort(3).
The mprobe() function performs a consistency check on the block of
allocated memory pointed to by ptr. The mcheck() function should be
called beforehand (otherwise mprobe() returns MCHECK_DISABLED).
The following list describes the values returned by mprobe() or passed
as the mstatus argument when abortfunc is invoked:
MCHECK_DISABLED (mprobe() only)
mcheck() was not called before the first memory allocation func-
tion was called. Consistency checking is not possible.
MCHECK_OK (mprobe() only)
No inconsistency detected.
MCHECK_HEAD
Memory preceding an allocated block was clobbered.
MCHECK_TAIL
Memory following an allocated block was clobbered.
MCHECK_FREE
A block of memory was freed twice.
RETURN VALUE
mcheck() and mcheck_pedantic() return 0 on success, or -1 on error.
VERSIONS
The mcheck_pedantic() and mcheck_check_all() functions are available
since glibc 2.2. The mcheck() and mprobe() functions are present since
at least glibc 2.0
CONFORMING TO
These functions are GNU extensions.
NOTES
Linking a program with -lmcheck and using the MALLOC_CHECK_ environment
variable (described in mallopt(3)) cause the same kinds of errors to be
detected. But, using MALLOC_CHECK_ does not require the application to
be relinked.
EXAMPLE
The program below calls mcheck() with a NULL argument and then frees
the same block of memory twice. The following shell session demon-
strates what happens when running the program:
$ ./a.out
About to free
About to free a second time
block freed twice
Aborted (core dumped)
Program source
#include <stdlib.h>
#include <stdio.h>
#include <mcheck.h>
int
main(int argc, char *argv[])
{
char *p;
if (mcheck(NULL) != 0) {
fprintf(stderr, "mcheck() failed\n");
exit(EXIT_FAILURE);
}
p = malloc(1000);
fprintf(stderr, "About to free\n");
free(p);
fprintf(stderr, "\nAbout to free a second time\n");
free(p);
exit(EXIT_SUCCESS);
}
SEE ALSO
malloc(3), mallopt(3), mtrace(3)
COLOPHON
This page is part of release 3.69 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
http://www.kernel.org/doc/man-pages/.
GNU 2014-01-11 MCHECK(3)
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