title: valgrind memcheck gives message "in a rw- anonymous segment"
body: <p>I'm using massif to debug heap increasing issue with a binary program which is running long long time. But it report:</p>
  
  <pre><code>valgrind: m_mallocfree.c:280 (mk_plain_bszB): Assertion 'bszB != 0' failed.
  valgrind: This is probably caused by your program erroneously writing past the
  end of a heap block and corrupting heap metadata.  If you fix any
  invalid writes reported by Memcheck, this assertion failure will
  probably go away.  Please try that before reporting this as a bug.
  host stacktrace:
  ==21766==    at 0x58007769: show_sched_status_wrk (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x58007A44: report_and_quit (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x58007C77: vgPlain_assert_fail (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x58013D01: vgPlain_arena_free (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x5805CAE2: do_client_request (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x5805DCFE: vgPlain_scheduler (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x58011560: final_tidyup (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x5801191B: shutdown_actions_NORETURN (in /usr/lib64/valgrind/massif-amd64-linux)
  ==21766==    by 0x5808F42C: run_a_thread_NORETURN (in /usr/lib64/valgrind/massif-amd64-linux)
  
  sched status:
    running_tid=1
  
  Thread 1: status = VgTs_Runnable (lwpid 21766)
  ==21766==    at 0x4A06F16: free (vg_replace_malloc.c:529)
  ==21766==    by 0x3CD630C24A: free_mem (in /lib64/libc-2.5.so)
  ==21766==    by 0x3CD630BE41: __libc_freeres (in /lib64/libc-2.5.so)
  ==21766==    by 0x480368A: _vgnU_freeres (vg_preloaded.c:77)
  ==21766==    by 0x3CD6233224: exit (exit.c:90)
  ==21766==    by 0x3CD621D9FA: (below main) (libc-start.c:262)
  </code></pre>
  
  <p>So I tryed valgrind --tool=memcheck -v, and it report:</p>
  
  <pre><code>==21789== HEAP SUMMARY:
  ==21789==     in use at exit: 0 bytes in 0 blocks
  ==21789==   total heap usage: 7,015 allocs, 7,016 frees, 805,222 bytes allocated
  ==21789==
  ==21789== All heap blocks were freed -- no leaks are possible
  ==21789==
  ==21789== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 6 from 4)
  ==21789==
  ==21789== 1 errors in context 1 of 1:
  ==21789== Invalid free() / delete / delete[] / realloc()
  ==21789==    at 0x4A08B56: free (vg_replace_malloc.c:529)
  ==21789==    by 0x3CD630C24A: free_mem (in /lib64/libc-2.5.so)
  ==21789==    by 0x3CD630BE41: __libc_freeres (in /lib64/libc-2.5.so)
  ==21789==    by 0x480368A: _vgnU_freeres (vg_preloaded.c:77)
  ==21789==    by 0x3CD6233224: exit (exit.c:90)
  ==21789==    by 0x3CD621D9FA: (below main) (libc-start.c:262)
  ==21789==  Address 0x6374c98 is in a rw- anonymous segment
  ==21789==
  --21789--
  --21789-- used_suppression:      6 dl-hack3 /usr/lib64/valgrind/default.supp:1239
  ==21789==
  ==21789== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 6 from 4)
  </code></pre>
  
  <p>I got no idea for something error below main.</p>