Memory leak while loading external library?

[elpres]

Here is the code:

when defined(windows):
  const libz = "zlib1.dll"
elif defined(macosx):
  const libz = "libz.dylib"
else:
  const libz = "libz.so.1"

type
  GzFile* = pointer

proc gzopen*(path: cstring, mode: cstring): GzFile{.cdecl, dynlib: libz, importc: "gzopen".}
proc gzclose*(thefile: GzFile) {.cdecl, dynlib: libz, importc: "gzclose".}

when isMainModule:
  let infile = gzopen("test.txt.gz", "rb")
  infile.gzclose

And the valgrind log:

% valgrind --leak-check=full --show-leak-kinds=all ./gzip
==6214== Memcheck, a memory error detector
==6214== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==6214== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==6214== Command: ./gzip
==6214== 
==6214== 
==6214== HEAP SUMMARY:
==6214==     in use at exit: 1,624 bytes in 4 blocks
==6214==   total heap usage: 7 allocs, 3 frees, 1,924 bytes allocated
==6214== 
==6214== 19 bytes in 1 blocks are still reachable in loss record 1 of 4
==6214==    at 0x4C29F90: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6214==    by 0x4005419: local_strdup (in /usr/lib/ld-2.20.so)
==6214==    by 0x400879E: _dl_map_object (in /usr/lib/ld-2.20.so)
==6214==    by 0x40134C2: dl_open_worker (in /usr/lib/ld-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4012E92: _dl_open (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37038: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37608: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x4E370D0: dlopen (in /usr/lib/libdl-2.20.so)
==6214==    by 0x410EEC: nimLoadLibrary (in /home/elpres/Code/nim/illumina/gzip)
==6214==    by 0x41D9F5: gzipDatInit (in /home/elpres/Code/nim/illumina/gzip)
==6214== 
==6214== 19 bytes in 1 blocks are still reachable in loss record 2 of 4
==6214==    at 0x4C29F90: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6214==    by 0x400B24F: _dl_new_object (in /usr/lib/ld-2.20.so)
==6214==    by 0x4006303: _dl_map_object_from_fd (in /usr/lib/ld-2.20.so)
==6214==    by 0x400861B: _dl_map_object (in /usr/lib/ld-2.20.so)
==6214==    by 0x40134C2: dl_open_worker (in /usr/lib/ld-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4012E92: _dl_open (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37038: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37608: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x4E370D0: dlopen (in /usr/lib/libdl-2.20.so)
==6214==    by 0x410EEC: nimLoadLibrary (in /home/elpres/Code/nim/illumina/gzip)
==6214== 
==6214== 408 bytes in 1 blocks are still reachable in loss record 3 of 4
==6214==    at 0x4C2C080: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6214==    by 0x40109DD: _dl_check_map_versions (in /usr/lib/ld-2.20.so)
==6214==    by 0x4013A29: dl_open_worker (in /usr/lib/ld-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4012E92: _dl_open (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37038: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37608: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x4E370D0: dlopen (in /usr/lib/libdl-2.20.so)
==6214==    by 0x410EEC: nimLoadLibrary (in /home/elpres/Code/nim/illumina/gzip)
==6214==    by 0x41D9F5: gzipDatInit (in /home/elpres/Code/nim/illumina/gzip)
==6214==    by 0x41D81C: PreMainInner (in /home/elpres/Code/nim/illumina/gzip)
==6214== 
==6214== 1,178 bytes in 1 blocks are still reachable in loss record 4 of 4
==6214==    at 0x4C2C080: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6214==    by 0x400AF36: _dl_new_object (in /usr/lib/ld-2.20.so)
==6214==    by 0x4006303: _dl_map_object_from_fd (in /usr/lib/ld-2.20.so)
==6214==    by 0x400861B: _dl_map_object (in /usr/lib/ld-2.20.so)
==6214==    by 0x40134C2: dl_open_worker (in /usr/lib/ld-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4012E92: _dl_open (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37038: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x400F0F3: _dl_catch_error (in /usr/lib/ld-2.20.so)
==6214==    by 0x4E37608: ??? (in /usr/lib/libdl-2.20.so)
==6214==    by 0x4E370D0: dlopen (in /usr/lib/libdl-2.20.so)
==6214==    by 0x410EEC: nimLoadLibrary (in /home/elpres/Code/nim/illumina/gzip)
==6214== 
==6214== LEAK SUMMARY:
==6214==    definitely lost: 0 bytes in 0 blocks
==6214==    indirectly lost: 0 bytes in 0 blocks
==6214==      possibly lost: 0 bytes in 0 blocks
==6214==    still reachable: 1,624 bytes in 4 blocks
==6214==         suppressed: 0 bytes in 0 blocks
==6214== 
==6214== For counts of detected and suppressed errors, rerun with: -v
==6214== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

[zielmicha]

Leaking memory when loading dynamic libraries is not harmful - they are going to be loaded only once per process lifetime.

[Araq]

And apart from that Valgrind doesn't know anything about Nim's memory manager.