mcheck(3) — Linux manual page


mcheck(3)               Library Functions Manual               mcheck(3)

NAME         top

       mcheck, mcheck_check_all, mcheck_pedantic, mprobe - heap
       consistency checking

LIBRARY         top

       Standard C library (libc, -lc)

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 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

       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

       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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                Attribute     Value              │
       │ mcheck(),                │ Thread safety │ MT-Unsafe          │
       │ mcheck_pedantic(),       │               │ race:mcheck        │
       │ mcheck_check_all(),      │               │ const:malloc_hooks │
       │ mprobe()                 │               │                    │

STANDARDS         top


HISTORY         top

              glibc 2.2.

              glibc 2.0.

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 <mcheck.h>
       #include <stdio.h>
       #include <stdlib.h>

           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

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Linux man-pages 6.9.1          2024-06-15                      mcheck(3)

Pages that refer to this page: malloc(3)malloc_hook(3)mallopt(3)mtrace(3)