mcheck

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



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(), │ Thread safety │ MT-Unsafe race:mcheck │
       │mcheck_check_all(), mprobe() │               │ 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.

EXAMPLES
       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 5.09 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                                2020-06-09                          MCHECK(3)