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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
MCHECK(3) Linux Programmer's Manual MCHECK(3)
mcheck, mcheck_check_all, mcheck_pedantic, mprobe - heap consistency
checking
#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);
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.
mcheck() and mcheck_pedantic() return 0 on success, or -1 on error.
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
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────┬───────────────┬───────────────────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────┼───────────────┼───────────────────────┤
│mcheck(), mcheck_pedantic(), │ Thread safety │ MT-Unsafe race:mcheck │
│mcheck_check_all(), mprobe() │ │ const:malloc_hooks │
└─────────────────────────────┴───────────────┴───────────────────────┘
These functions are GNU extensions.
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.
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);
}
malloc(3), mallopt(3), mtrace(3)
This page is part of release 4.12 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 2015-05-07 MCHECK(3)
Pages that refer to this page: malloc(3), malloc_hook(3), mallopt(3), mtrace(3)