Re: [Valgrind-users] __malloc_hook

[Amir S. <ki...@gm...>]

That works perfectly. Thanks John!

I had to add a Valgrind suppression as dlsym() always leaves 20-bytes
"still reachable" block.

---------
{
   dlsym in malloc_fail.cpp:malloc()
   Memcheck:Leak
   fun:calloc
   obj:/lib/libdl-2.5.so
   fun:dlsym
   fun:malloc
   ...
}
---------

For anyone interested, this is the code I ended up using:

---------
/*
 * Copyright (c) 2012, Juniper Networks, Inc.
 * All rights reserved.
 */
#include "malloc_fail.h"

#include <cxxtest/TestSuite.h>

#define _GNU_SOURCE 1
#include <dlfcn.h>

static unsigned int malloc_num_to_fail = 0;

void malloc_dbg_set_num_to_fail(unsigned int num)
{
	malloc_num_to_fail = num;
}

void *malloc(size_t size)
{
	if (malloc_num_to_fail)
	{
		if (--malloc_num_to_fail == 0)
		{
			printf("Deliberate memory allocation failure [size=%zu]\n", size);
			return NULL;
		}
	}

	void * (*real_malloc) (size_t) = (void * (*) (size_t))
dlsym(RTLD_NEXT, "malloc");
	return real_malloc(size);
}
-------

> The intended way to do this is by "intercepting", "superseding",
> or "over-riding" the symbol 'malloc':  Make your own shared library
> containing a malloc() routine, and load it into your app via
> environment variable LD_PRELOAD, so that calls from the app to
> malloc() go to your LD_PRELOADed library.  Your malloc can do
> whatever it wants, probably including finding the "real" malloc
> by dlsym(RTLD_NEXT, "malloc") and calling that as a subroutine.
> See the manual page for dlsym.  Remember to "#define _GNU_SOURCE 1"
> before "#include <dlfcn.h>".