Manpage of MCHECK

MCHECK

Section: Linux Programmer's Manual (3)
Updated: 2015-05-07
Index
 

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 -lmcheckinserts 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 abortfuncis invoked with a single argument, mstatus, that indicates what type of inconsistency was detected. If abortfuncis NULL, a default function prints an error message on stderrand 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 mstatusargument when abortfuncis 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).
InterfaceAttributeValue
mcheck(), mcheck_pedantic(),
mcheck_check_all(), mprobe()
Thread safetyMT-Unsafe race:mcheck
const:malloc_hooks

 

CONFORMING TO

These functions are GNU extensions.  

NOTES

Linking a program with -lmcheckand 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.outAbout 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)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
VERSIONS
ATTRIBUTES
CONFORMING TO
NOTES
EXAMPLE
Program source
SEE ALSO

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