OCaml C interface undefined reference to "caml_local_roots"

Hi !

I’m trying to compile a very simple C++ project for OCaml. Here is what I did so far:

#include <iostream>
#include <string>

#include "osm.hpp"

extern "C" {
    #include <caml/mlvalues.h>
    #include <caml/memory.h>
    #include <caml/alloc.h>
    #include <caml/custom.h>
}

extern "C"
CAMLprim value osm_from_file(value file)
{
    CAMLparam1 (file);
    std::string fileName = String_val(file);

    std::cout << fileName << std::endl;

    CAMLreturn (Val_unit);
}

extern "C"
CAMLprim value osm_read_data(value osmObj)
{
    CAMLparam1 (osmObj);

    std::cout << "Testing" << std::endl;

    CAMLreturn (Val_unit);
}

I’m compiling it using CMake for the “osm” little class I’m writing and Dune to link it with my OCaml project.

Here is what I get while building my project with Dune.

$>> dune build
    ocamlopt project/bin/main.exe (exit 2)
(cd _build/default && /home/user/.opam/4.12.0/bin/ocamlopt.opt -w @1..3@5..28@30..39@43@46..47@49..57@61..62-40 -strict-sequence -strict-formats -short-paths -keep-locs -g -o project/bin/main.exe project/lib/project.cmxa project/bin/osm/cosm.cmxa -I project/bin/osm project/bin/.main.eobjs/native/dune__exe.cmx project/bin/.main.eobjs/native/dune__exe__Map.cmx project/bin/.main.eobjs/native/dune__exe__Main.cmx -linkall -cclib -lstdc++)
/usr/bin/ld: project/bin/osm/libbinding.a(binding.cpp.o): in function `osm_from_file':
binding.cpp:(.text+0x55e): undefined reference to `caml_local_roots'
/usr/bin/ld: binding.cpp:(.text+0x56c): undefined reference to `caml_local_roots'
/usr/bin/ld: binding.cpp:(.text+0x57b): undefined reference to `caml_local_roots'
/usr/bin/ld: binding.cpp:(.text+0x61f): undefined reference to `caml_local_roots'
/usr/bin/ld: project/bin/osm/libbinding.a(binding.cpp.o): in function `osm_read_data':
binding.cpp:(.text+0x6ba): undefined reference to `caml_local_roots'
/usr/bin/ld: project/bin/osm/libbinding.a(binding.cpp.o):binding.cpp:(.text+0x6c5): more undefined references to `caml_local_roots' follow
collect2: error: ld returned 1 exit status
File "caml_startup", line 1:
Error: Error during linking (exit code 1)

caml_local_roots should be defined in “caml/memory.h” but it looks like there is a problem while linking this file with my project.

Here is my Dune file to compile the “osm” library.

(library
    (name cosm)
    (c_library_flags :standard -lstdc++ -lbz2 -lexpat -lz -lpthread)
    (foreign_archives binding)
)

(rule
    (deps (source_tree osm))
    (targets libbinding.a dllbinding.so)
    (action
        (no-infer
            (progn
                (chdir osm (run make))
                (copy osm/libbindingsh.so dllbinding.so)
                (copy osm/libbinding.a libbinding.a)
))))

Does anyone has an idea on how can I solve this problem ?

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