[Bug 883775] Re: non cumulative memory leak in dlopen/dlclose

[Ivan Sorokin]

Thank you, Martin. Suppression seems to be the only feasible solution,
because libc6 code is really complicated in this function.

Should we report this bug upstream or let it stay here? eglibc
(http://www.eglibc.org/issues/) bug-tracker seems to be not very
popular.

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https://bugs.launchpad.net/bugs/883775

Title:
  non cumulative memory leak in dlopen/dlclose

Status in “eglibc” package in Ubuntu:
  Confirmed

Bug description:
  Ubuntu 11.10, libc6 2.13-20ubuntu5.

  After calling dlopen/dlclose few blocks of memory left unfreed. They
  number is not grow when dlopen/dlclose are called several times.

  This is not fatal bug, but it makes it harder to find memory leaks in
  other parts of program.

  Source code:

  #include <dlfcn.h>
  #include <stdio.h>
  #include <stdlib.h>

  void print_dlerror()
  {
        char const* msg = dlerror();
        if (msg == NULL)
           fprintf(stderr, "unknown error at dynamic linking");
        else
           fprintf(stderr, "dynamic linking error: %s", msg);
  }

  int main()
  {
     void* asound = dlopen("/usr/lib/x86_64-linux-gnu/libasound.so.2", RTLD_LAZY);
     if (asound == NULL)
     {
        print_dlerror();
        return EXIT_FAILURE;
     }

     printf("module is loaded successfully: %p\n", asound);

     dlclose(asound);
     
     return EXIT_SUCCESS;
  }

  Valgrind output:

  valgrind --leak-check=full --show-reachable=yes -v ./a.out

  ==2114== HEAP SUMMARY:
  ==2114==     in use at exit: 3,361 bytes in 12 blocks
  ==2114==   total heap usage: 22 allocs, 10 frees, 6,638 bytes allocated
  ==2114== 
  ==2114== Searching for pointers to 12 not-freed blocks
  ==2114== Checked 114,056 bytes
  ==2114== 
  ==2114== 64 bytes in 2 blocks are still reachable in loss record 1 of 6
  ==2114==    at 0x4C28F9F: malloc (vg_replace_malloc.c:236)
  ==2114==    by 0x40141B6: _dl_close_worker (dl-close.c:374)
  ==2114==    by 0x401469D: _dl_close (dl-close.c:754)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4E3052E: _dlerror_run (dlerror.c:164)
  ==2114==    by 0x4E3000E: dlclose (dlclose.c:48)
  ==2114==    by 0x4007AA: main (in /home/ivan/a.out)
  ==2114== 
  ==2114== 71 bytes in 2 blocks are still reachable in loss record 2 of 6
  ==2114==    at 0x4C28F9F: malloc (vg_replace_malloc.c:236)
  ==2114==    by 0x40085B3: _dl_map_object (dl-load.c:162)
  ==2114==    by 0x400C8A1: openaux (dl-deps.c:65)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x400CF65: _dl_map_object_deps (dl-deps.c:247)
  ==2114==    by 0x4012BA6: dl_open_worker (dl-open.c:263)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4013379: _dl_open (dl-open.c:569)
  ==2114==    by 0x4E2FF25: dlopen_doit (dlopen.c:67)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4E3052E: _dlerror_run (dlerror.c:164)
  ==2114==    by 0x4E2FFC0: dlopen@@GLIBC_2.2.5 (dlopen.c:88)
  ==2114== 
  ==2114== 71 bytes in 2 blocks are still reachable in loss record 3 of 6
  ==2114==    at 0x4C28F9F: malloc (vg_replace_malloc.c:236)
  ==2114==    by 0x400B42C: _dl_new_object (dl-object.c:161)
  ==2114==    by 0x40065B5: _dl_map_object_from_fd (dl-load.c:957)
  ==2114==    by 0x400831C: _dl_map_object (dl-load.c:2250)
  ==2114==    by 0x400C8A1: openaux (dl-deps.c:65)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x400CF65: _dl_map_object_deps (dl-deps.c:247)
  ==2114==    by 0x4012BA6: dl_open_worker (dl-open.c:263)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4013379: _dl_open (dl-open.c:569)
  ==2114==    by 0x4E2FF25: dlopen_doit (dlopen.c:67)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114== 
  ==2114== 112 bytes in 2 blocks are still reachable in loss record 4 of 6
  ==2114==    at 0x4C28F9F: malloc (vg_replace_malloc.c:236)
  ==2114==    by 0x400D016: _dl_map_object_deps (dl-deps.c:470)
  ==2114==    by 0x4012BA6: dl_open_worker (dl-open.c:263)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4013379: _dl_open (dl-open.c:569)
  ==2114==    by 0x4E2FF25: dlopen_doit (dlopen.c:67)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4E3052E: _dlerror_run (dlerror.c:164)
  ==2114==    by 0x4E2FFC0: dlopen@@GLIBC_2.2.5 (dlopen.c:88)
  ==2114==    by 0x400771: main (in /home/ivan/a.out)
  ==2114== 
  ==2114== 696 bytes in 2 blocks are still reachable in loss record 5 of 6
  ==2114==    at 0x4C279F2: calloc (vg_replace_malloc.c:467)
  ==2114==    by 0x4010329: _dl_check_map_versions (dl-version.c:300)
  ==2114==    by 0x4012EC0: dl_open_worker (dl-open.c:269)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4013379: _dl_open (dl-open.c:569)
  ==2114==    by 0x4E2FF25: dlopen_doit (dlopen.c:67)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4E3052E: _dlerror_run (dlerror.c:164)
  ==2114==    by 0x4E2FFC0: dlopen@@GLIBC_2.2.5 (dlopen.c:88)
  ==2114==    by 0x400771: main (in /home/ivan/a.out)
  ==2114== 
  ==2114== 2,347 bytes in 2 blocks are still reachable in loss record 6 of 6
  ==2114==    at 0x4C279F2: calloc (vg_replace_malloc.c:467)
  ==2114==    by 0x400B1BD: _dl_new_object (dl-object.c:77)
  ==2114==    by 0x40065B5: _dl_map_object_from_fd (dl-load.c:957)
  ==2114==    by 0x400831C: _dl_map_object (dl-load.c:2250)
  ==2114==    by 0x400C8A1: openaux (dl-deps.c:65)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x400CF65: _dl_map_object_deps (dl-deps.c:247)
  ==2114==    by 0x4012BA6: dl_open_worker (dl-open.c:263)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114==    by 0x4013379: _dl_open (dl-open.c:569)
  ==2114==    by 0x4E2FF25: dlopen_doit (dlopen.c:67)
  ==2114==    by 0x400E995: _dl_catch_error (dl-error.c:178)
  ==2114== 
  ==2114== LEAK SUMMARY:
  ==2114==    definitely lost: 0 bytes in 0 blocks
  ==2114==    indirectly lost: 0 bytes in 0 blocks
  ==2114==      possibly lost: 0 bytes in 0 blocks
  ==2114==    still reachable: 3,361 bytes in 12 blocks
  ==2114==         suppressed: 0 bytes in 0 blocks

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