mcheck_check_all(3) — Linux manual page


MCHECK(3)                 Linux Programmer's Manual                MCHECK(3)

NAME         top

       mcheck,  mcheck_check_all, mcheck_pedantic, mprobe - heap consistency

SYNOPSIS         top

       #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         top

       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

       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.

              Memory preceding an allocated block was clobbered.

              Memory following an allocated block was clobbered.

              A block of memory was freed twice.

RETURN VALUE         top

       mcheck() and mcheck_pedantic() return 0 on success, or -1 on error.

VERSIONS         top

       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         top

       For an explanation of the terms used in this section, see

       │Interface                    Attribute     Value                 │
       │mcheck(), mcheck_pedantic(), │ Thread safety │ MT-Unsafe race:mcheck │
       │mcheck_check_all(), mprobe() │               │ const:malloc_hooks    │

CONFORMING TO         top

       These functions are GNU extensions.

NOTES         top

       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.

EXAMPLES         top

       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>

       main(int argc, char *argv[])
           char *p;

           if (mcheck(NULL) != 0) {
               fprintf(stderr, "mcheck() failed\n");


           p = malloc(1000);

           fprintf(stderr, "About to free\n");
           fprintf(stderr, "\nAbout to free a second time\n");


SEE ALSO         top

       malloc(3), mallopt(3), mtrace(3)

COLOPHON         top

       This page is part of release 5.08 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

GNU                              2020-06-09                        MCHECK(3)