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

NAME
       mallochook,  mallocinitializehook, memalignhook, freehook,
       reallochook, aftermorecorehook - malloc debugging variables

SYNOPSIS
       #include 

       void *(*mallochook)(sizet size, const void *caller);

       void *(*reallochook)(void *ptr, sizet size, const void *caller);

       void *(*memalignhook)(sizet alignment, sizet size,
                                const void *caller);

       void (*freehook)(void *ptr, const void *caller);

       void (*mallocinitializehook)(void);

       void (*aftermorecorehook)(void);

DESCRIPTION
       The GNU C library lets you modify  the  behavior  of  malloc(3),  real‐
       loc(3),  and free(3) by specifying appropriate hook functions.  You can
       use these hooks to help you debug  programs  that  use  dynamic  memory
       allocation, for example.

       The  variable  mallocinitializehook  points  at  a function that is
       called once when the malloc implementation is initialized.  This  is  a
       weak  variable, so it can be overridden in the application with a defi‐
       nition like the following:

           void (*mallocinitializehook)(void) = myinithook;

       Now the function myinithook() can do the initialization of all hooks.

       The four functions pointed to by mallochook, reallochook, mema‐
       lignhook,  freehook  have a prototype like the functions malloc(3),
       realloc(3), memalign(3), free(3), respectively, except that they have a
       final  argument  caller  that  gives  the address of the caller of mal‐
       loc(3), etc.

       The variable aftermorecorehook points at a function that is  called
       each time after sbrk(2) was asked for more memory.

CONFORMING TO
       These functions are GNU extensions.

NOTES
       The  use of these hook functions is not safe in multithreaded programs,
       and they are now deprecated.  Programmers should instead preempt  calls
       to  the  relevant functions by defining and exporting functions such as
       "malloc" and "free".

EXAMPLE
       Here is a short example of how to use these variables.

       #include 
       #include 

       /* Prototypes for our hooks.  */
       static void myinithook(void);
       static void *mymallochook(sizet, const void *);

       /* Variables to save original hooks. */
       static void *(*oldmallochook)(sizet, const void *);

       /* Override initializing hook from the C library. */
       void (*mallocinitializehook) (void) = myinithook;

       static void
       myinithook(void)
       {
           oldmallochook = mallochook;
           mallochook = mymallochook;
       }

       static void *
       mymallochook(sizet size, const void *caller)
       {
           void *result;

           /* Restore all old hooks */
           mallochook = oldmallochook;

           /* Call recursively */
           result = malloc(size);

           /* Save underlying hooks */
           oldmallochook = mallochook;

           /* printf() might call malloc(), so protect it too. */
           printf("malloc(%u) called from %p returns %p\n",
                   (unsigned int) size, caller, result);

           /* Restore our own hooks */
           mallochook = mymallochook;

           return result;
       }

SEE ALSO
       mallinfo(3), malloc(3), mcheck(3), mtrace(3)

COLOPHON
       This page is part of release 3.53 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



GNU                               2010-10-13                    MALLOCHOOK(3)