Memory problems with LibGit2 initialization - libgit2

Question

When I initialize and shutdown LibGit2 I am left with reachable memory and/or errors.
My test systems are Ubuntu 18.04 with libgit2 0.26 where g++ -v gives me gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1) and a FreeBSD 11.3 VM with libgit 0.28.3 where, unfortunately, I can't copy & paste from. Here g++ -v gives gcc version 9.2.0 (FreeBSD Ports Collection.
This is a minimal example:
#include <git2.h>
int main () {
git_libgit2_init();
git_libgit2_shutdown();
return 0;
}
On Ubuntu I run the following:
➜ libelektra git:(libgit_test) ✗ g++ minimal.c -lgit2 && valgrind ./a.out
==1174== Memcheck, a memory error detector
==1174== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1174== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==1174== Command: ./a.out
==1174==
==1174==
==1174== HEAP SUMMARY:
==1174== in use at exit: 192 bytes in 12 blocks
==1174== total heap usage: 1,354 allocs, 1,342 frees, 107,044 bytes allocated
==1174==
==1174== LEAK SUMMARY:
==1174== definitely lost: 0 bytes in 0 blocks
==1174== indirectly lost: 0 bytes in 0 blocks
==1174== possibly lost: 0 bytes in 0 blocks
==1174== still reachable: 192 bytes in 12 blocks
==1174== suppressed: 0 bytes in 0 blocks
==1174== Rerun with --leak-check=full to see details of leaked memory
==1174==
==1174== For counts of detected and suppressed errors, rerun with: -v
==1174== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Why do I have reachable memory, when the very first example from the documentation says that git_libgit2_shutdown(); should clean everything up?
While the Valgrind documentation says that some reachable memory might be ok, things get quite wild on FreeBSD. I have some screenshots of the VM
One Two Three.
How can I avoid this?
One additional remark on different memory handling. My goal is to use the git_merge_file function in this project. It should look something like this:
#include <git2.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
int main () {
git_libgit2_init();
sleep (1);
git_merge_file_result out = { 0 }; // out.ptr will not receive a terminating null character
git_merge_file_input libgit_base;
git_merge_file_input libgit_our;
git_merge_file_input libgit_their;
git_merge_file_init_input(&libgit_base, GIT_MERGE_FILE_INPUT_VERSION);
git_merge_file_init_input(&libgit_our, GIT_MERGE_FILE_INPUT_VERSION);
git_merge_file_init_input(&libgit_their, GIT_MERGE_FILE_INPUT_VERSION);
libgit_base.ptr = "A";
libgit_base.size = strlen("A");
libgit_our.ptr = "A";
libgit_our.size = strlen("A");
libgit_their.ptr = "A";
libgit_their.size = strlen("A");
int exitCode = git_merge_file (&out, &libgit_base, &libgit_our, &libgit_their, 0);
printf("Code is %d\n", exitCode);
git_merge_file_result_free (&out);
git_libgit2_shutdown();
sleep (1);
return 0;
}
When I remove initialization and/or shutdown I sometimes got 0 still reachable memory on Ubuntu but segmentation faults on FreeBSD. Is it worth giving this a closer look or is such a difference in behavior normal when ignoring the that LibGit must be initialized?
In the screenshots of the BSD VM __pthread_once is visible as a source of problems. This and __pthread_once_slow seem to be involved in all the errors: The 192 bytes on Ubuntu in the beginning, the more advanced example at the bottom with BSD and Ubuntu and also my real application.

Answer 1

As far as I can see, there's nothing wrong with your code, or the Valgrind report by itself, as as you've pointed out:
"still reachable" means your program is probably ok -- it didn't free some memory it could have. This is quite common and often reasonable. Don't use --show-reachable=yes if you don't want to see these reports.
Hence, it's likely the 192 bytes aren't really leaked, you've just managed to exit the program before the OS decided to grab back that block of memory — ie. it kept that block under the process's purview, as a optimisation for the next allocation to be made. In this case, the process just exited, so that memory will have to be reclaimed at process termination, and I think that's what "still reachable" means — memory that is fine, and will be reclaimed normally. Hopefully 😉.
The Valgrind errors on FreeBSD aren't allocation problems, but use of an uninitialized zone of memory. They don't look to be inside libgit2 but OpenSSL itself, while parsing certificates (?). You can find the underlying OpenSSL initialization starting from here.
Is it worth giving this a closer look or is such a difference in behavior normal when ignoring the that LibGit must be initialized?
I'm tempted to say no, and yes. The code is now prodding a memory location that contains random garbage instead of an stack-allocated pthread_something. Segfaults are bound to happen randomly.
HTH !