MCHECK
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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
malloc(3)
family of memory-allocation functions.
These hooks cause certain 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 immediately 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 difficult to ensure, linking the program with
-lmcheck
inserts an implicit call to
mcheck()
(with a NULL argument)
before the first call to a memory-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 allocated 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 function 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).
| Interface | Attribute | Value
|
mcheck(),
mcheck_pedantic(),
mcheck_check_all(),
mprobe()
| Thread safety |
MT-Unsafe race:mcheck
const:malloc_hooks
|
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 demonstrates 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 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLE
-
- Program source
-
- SEE ALSO
-
- COLOPHON
-
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