Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


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


     mcheck,  mcheck_check_all,  mcheck_pedantic,  mprobe - heap consistency


     #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  mal-
     loc(3)  family  of memory-allocation functions.  These hooks cause cer-
     tain 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 imme-
     diately 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 diffi-
     cult  to  ensure, linking the program with -lmcheck inserts an implicit
     call to mcheck() (with a NULL argument) before the first call to a mem-
     ory-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 allo-
     cated 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 func-
            tion 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.


     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
     |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 demon-
     strates 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");
         p = malloc(1000);
         fprintf(stderr, "About to free\n");
         fprintf(stderr, "\nAbout to free a second time\n");
         exit(EXIT_SUCCESS); }


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


     This  page  is  part of release 4.16 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 2017-09-15 MCHECK(3)

/data/webs/external/dokuwiki/data/pages/man/mcheck.txt · Last modified: 2019/05/17 09:32 by

Was this page helpful?-11+1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki