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mcheck(3)
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,
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
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
allbox; lbw28 lb lbw21 l l l. Interface Attribute Value T{ mcheck(),
mcheck_pedantic(),
mcheck_check_all(), mprobe() T} Thread safety T{ MT-Unsafe
race:mcheck
const:malloc_hooks T}
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 5.02 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/.
GNU 2019-03-06 MCHECK(3)