memory leak with core and ocaml 5.0

[sandreenko]

Hello JaneStreet folks, I think I came accross a memory leak with Core and Ocaml 5.0, running this:

open Core

let main () =
  at_exit Gc.full_major;
  let str = Bigstring.create 11 in
  Bigstring.set str 0 'H';
  Bigstring.set str 1 'e';
  Bigstring.set str 2 'l';
  Bigstring.set str 3 'l';
  Bigstring.set str 4 'o';
  Bigstring.set str 5 ' ';
  Bigstring.set str 6 'w';
  Bigstring.set str 7 'o';
  Bigstring.set str 8 'r';
  Bigstring.set str 9 'l';
  Bigstring.set str 10 'd';
  Printf.printf "%s\n" (Bigstring.to_string str)


let () = main ()
let ( ) = Gc.full_major ()

with ocaml 5.0 and core 0.15.1 shows a memory leak and I suspect it is a core issue.

I first opened this issue in ocaml repo (ocaml/ocaml#12161) where @Octachron helped me and proved that it could be Core, not ocaml to blame.

Repro steps:

sudo dnf install libasan libubsan 
ocamlfind ocamlopt -thread -package core -linkpkg  -ccopt -fsanitize=address -ccopt -O0 hello.ml -o a.out
ASAN_OPTIONS=detect_leaks=1 ./a.out 

output:

Hello world

=================================================================
==3272424==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 96 byte(s) in 1 object(s) allocated from:
    #0 0x3f1acf in malloc (/testOcaml5/__hello__/hello.opt+0x3f1acf)
    #1 0x804f93 in caml_thread_new_descriptor /.opam-switch/build/ocaml-variants.5.0.0+options/otherlibs/systhreads/st_pthreads.h:244:16
    #2 0x805123 in caml_thread_domain_initialize_hook /.opam-switch/build/ocaml-variants.5.0.0+options/otherlibs/systhreads/st_stubs.c:427:23
    #3 0x8057c6 in caml_thread_initialize /.opam-switch/build/ocaml-variants.5.0.0+options/otherlibs/systhreads/st_stubs.c:473:3
    #4 0x832312 in caml_c_call (/testOcaml5/__hello__/hello.opt+0x832312)

Direct leak of 40 byte(s) in 1 object(s) allocated from:
    #0 0x3f1acf in malloc (/testOcaml5/__hello__/hello.opt+0x3f1acf)
    #1 0x82dfc9 in caml_ml_mutex_new /.opam-switch/build/ocaml-variants.5.0.0+options/runtime/sync_posix.h:44:7
    #2 0x832312 in caml_c_call (/testOcaml5/__hello__/hello.opt+0x832312)

Direct leak of 11 byte(s) in 4 object(s) allocated from:
    #0 0x3f1acf in malloc (/testOcaml5/__hello__/hello.opt+0x3f1acf)
    #1 0x80c79c in caml_ba_alloc /.opam-switch/build/ocaml-variants.5.0.0+options/runtime/bigarray.c:111:12
    #2 0x80c99c in caml_ba_create /.opam-switch/build/ocaml-variants.5.0.0+options/runtime/bigarray.c:521:10
    #3 0x832312 in caml_c_call (/testOcaml5/__hello__/hello.opt+0x832312)

SUMMARY: AddressSanitizer: 147 byte(s) leaked in 6 allocation(s).