Heap Checker treats all memory ranges mapped by libpthread as live, with the exception
of those ranges which contain the stack pointer of a running thread. On Linux, libpthread
does not immediately unmap the stack on thread death. As a result, stacks of dead threads
may still exist in memory and will be treated as live by Heap Checker.

Reproducer:

#include <pthread.h>                                                              


#include <stdio.h>                                                                


#include <stdlib.h>                                                               





void *thread_func(void *) {
  // Print the stack range for reference.
  pthread_attr_t attr;
  pthread_getattr_np(pthread_self(), &attr);
  void *stackaddr;
  size_t stacksize;
  pthread_attr_getstack(&attr, &stackaddr, &stacksize);
  printf("Stack at %p-%p\n", stackaddr, (char *)stackaddr + stacksize);

  void *leaked = malloc(31337);
  printf("%p\n", leaked); // break optimization                                   


}                                                                                 





int main() {                                                                      


  pthread_t pid;                                                                  


  pthread_create(&pid, 0, thread_func, 0);                                        


  pthread_join(pid, 0);                                                           


  return 0;                                                                       


}

Build with -pthread and -ltcmalloc, run with HEAPCHECK=strict or HEAPCHECK=normal.
Heap checker reports no leaks, when in fact we have a leaked block of 31337 bytes.

Now run with HEAPCHECK=strict PERFTOOLS_VERBOSE=20.

On stdout:

Stack at 0x7f8792bf8000-0x7f87933f9000
[...]

On stderr:

[...]
Checking for whole-program memory leaks                                           


Disabling allocations from /lib/x86_64-linux-gnu/libpthread-2.15.so at depth 1:   


Global memory regions made by /lib/x86_64-linux-gnu/libpthread-2.15.so will be live
data                                                                              

Disabling allocations from /lib/x86_64-linux-gnu/ld-2.15.so at depth 2:           


Global memory regions made by /lib/x86_64-linux-gnu/ld-2.15.so will be live data  


Found 0 threads (from pid 32364)                                                  


Looking into ./a.out: 0x601000..0x602000                                          


Looking into [heap]: 0x21c3000..0x23dc000                                         


Looking into UNNAMED: 0x7f8792bf9000..0x7f87933f9000 
[...]
Looking for heap pointers in 0x7f8792bf9000 of 8388608 bytes                      


Got pointer into 0x22e0000 at +0 offset                                           


Found pointer to 0x22e0000 of 31337 bytes at 0x7f87933f7780 inside 0x7f8792bf9000 of
size 8388608
[...]