MCheck is not thread safe - can report false errors on multi threaded apps. mcheck.c uses the __malloc_hook (et al) feature of malloc.c & arena.c to intercept memory requests. During it's processing, it swaps the _hooks back to their original values and recursively calls the memory request in order to do the actual memory request. While this hook is swapped out, another thread could call the memory request and at that point get memory that bypassed mcheck. This memory will then be reported as corrupt if it is freed with the mcheck hook back in place. Possible fixes: 1) Add linkage to malloc.c's _int_malloc (el al) functions that would allow mcheck to access the memory allocation without having to go through the code implementing the hooks. 2) Change or add a new hook set that allows the hooker to wrapper the call, not just intercept it. 3) Write a separate memory pool routine for use in mcheck. (yuck).
This is by design. This can never be changed without breaking various ABIs.