Custom allocator: Valgrind shows 7 allocs, 0 frees, no leaks

Question

I am working on a clone of the malloc (3) functions (malloc, realloc and free for now).

I would like to add support for Valgrind. I'm using these docs. However, after adding calls to the VALGRIND_MEMPOOL_FREE, VALGRIND_MEMPOOL_ALLOC and VALGRIND_CREATE_MEMPOOL macros, I get the following from Valgrind:

==22303== HEAP SUMMARY:
==22303==     in use at exit: 0 bytes in 0 blocks
==22303==   total heap usage: 7 allocs, 0 frees, 2,039 bytes allocated
==22303== 
==22303== All heap blocks were freed -- no leaks are possible

This is despite my realloc calling VALGRIND_MEMPOOL_FREE and my free calling VALGRIND_MEMPOOL_FREE.

What could be the cause of this ?

Answer 1

What could be the cause of this ?

This is due to a bug in valgrind. See the link to the valgrind bug tracker in my comment to your answer.

From the other link in my comment:

A cursory search through the source code indicates that MEMPOOL_ALLOC calls new_block, which increments cmalloc_n_mallocs, but there is no corresponding change to cmalloc_n_frees in MEMPOOL_FREE.

/* valgrind.c */
#include <valgrind/valgrind.h>

int main(int argc, char *argv[]) {
    char pool[100];

    VALGRIND_CREATE_MEMPOOL(pool, 0, 0);
    VALGRIND_MEMPOOL_ALLOC(pool, pool, 8);
    VALGRIND_MEMPOOL_FREE(pool, pool);
    VALGRIND_DESTROY_MEMPOOL(pool);
    return 0;
}

$ gcc valgrind.c -g
$ valgrind --leak-check=full --show-leak-kinds=all ./a.out
==10186== Memcheck, a memory error detector
==10186== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==10186== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==10186== Command: ./a.out
==10186== 
==10186== 
==10186== HEAP SUMMARY:
==10186==     in use at exit: 0 bytes in 0 blocks
==10186==   total heap usage: 1 allocs, 0 frees, 8 bytes allocated
==10186== 
==10186== All heap blocks were freed -- no leaks are possible
==10186== 
==10186== For counts of detected and suppressed errors, rerun with: -v
==10186== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
$ 

Answer 2

Taken from here: http://valgrind.10908.n7.nabble.com/VALGRIND-MEMPOOL-FREE-not-reflected-in-heap-summary-td42789.html

A cursory search through the source code indicates that MEMPOOL_ALLOC calls new_block, which increments cmalloc_n_mallocs, but there is no corresponding change to cmalloc_n_frees in MEMPOOL_FREE. Here's a patch that increments it at the very end of MEMPOOL_FREE. This gives me the behavior I expect.