# Writing ctypes bindings to system shared libraries for bytecode targets via the dune ctypes stanza **URL:** \ **Category:** Ecosystem\ **Tags:** dune\ **Created:** [January 11, 2024, 3:12pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844 "2024-01-11T15:12:38Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![lukstafi](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lukstafi/32/3442_2.png) [@lukstafi](https://discuss.ocaml.org/u/lukstafi)\ **Post date:** [January 11, 2024, 3:12pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/1 "2024-01-11T15:12:38Z")
Working on [GitHub - lukstafi/ocaml-gccjit: OCaml bindings for libgccjit](https://github.com/lukstafi/ocaml-gccjit), I’m facing a problem with the same symptom as in this issue: [Add link flags ocamlmklib when using ctypes stubs](https://github.com/ocaml/dune/pull/8784). ```shell lukstafi@DESKTOP-6RRUNR4:~/ocaml-gccjit$ dune exec examples/tut01_hello_world.bc Fatal error: cannot load shared library dllgccjit_stubs Reason: /home/lukstafi/ocaml-gccjit/_build/install/default/lib/stublibs/dllgccjit_stubs.so: undefined symbol: gcc_jit_context_new_opaque_struct Aborted ``` The stubs library is found, but the underlying `libgccjit.so` library is not loaded. I tried various things like: adding `-linkall`; setting the env variables `DYLD_LIBRARY_PATH`, `LD_LIBRARY_PATH`, `CAML_LD_LIBRARY_PATH`; using `byte_complete` (doesn’t produce a `.bc` target); adding `(ocamlc_flags (-custom))` (breaks the build). Any ideas I could follow? ---
**Author:** ![nojb](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/nojb/32/519_2.png) [@nojb](https://discuss.ocaml.org/u/nojb)\ **Post date:** [January 11, 2024, 4:00pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/2 "2024-01-11T16:00:15Z")
> [@lukstafi](#): > > Any ideas I could follow? I’m not familiar with Ctypes, so don’t have much to offer. But it is often useful to look at the link flags recorded in `libgccjit.cma`/`libgccjit.cmxa`, which you can do with eg `ocamlobjinfo libgccjit.cma`. I think you would like to see at least `-lgccjit` and `-lgccjit_stubs` (in that order). If `-lgccjit` is missing then it means that some link-time flag is not being passed correctly somewhere. Cheers, Nicolas ---
**Author:** ![lukstafi](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lukstafi/32/3442_2.png) [@lukstafi](https://discuss.ocaml.org/u/lukstafi)\ **Post date:** [January 11, 2024, 5:01pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/3 "2024-01-11T17:01:20Z")
Yes, `-lgccjit` is neither in `Extra dynamically-loaded libraries:`, nor in the result of `ldd build/_default/lib/dllgccjit_stubs.so`. All flags are crammed into `Extra C object files:`. ---
**Author:** ![mobileink](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/mobileink/32/3295_2.png) [@mobileink](https://discuss.ocaml.org/u/mobileink)\ **Post date:** [January 11, 2024, 6:07pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/4 "2024-01-11T18:07:10Z")
> [@lukstafi](#): > > The stubs library is found, but the underlying `libgccjit.so` library is not loaded. Is it possible the lib is loaded but the symbol is stripped? I encountered this recently. The fix was `-Wl,-export-dynamic` (or `-export_dynamic` for mac). ---
**Author:** ![lukstafi](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lukstafi/32/3442_2.png) [@lukstafi](https://discuss.ocaml.org/u/lukstafi)\ **Post date:** [January 11, 2024, 6:24pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/5 "2024-01-11T18:24:18Z")
` -Wl,-export-dynamic` did not help. I managed to get ocamlobjinfo ==\> `Extra C options: -lgccjit -Wl,-export-dynamic`, but it did not help. Is there any way to pass additional parameters for `ocamlmklib`? Dune `-verbose`: ```shell Running[26]: (cd _build/default && /home/lukstafi/.opam/5.1.1/bin/ocamlmklib -g -o lib/gccjit_stubs lib/libgccjit __c_cout_generated_functions__ Gccjit_bindings__Functions.o) ``` ---
**Author:** ![nojb](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/nojb/32/519_2.png) [@nojb](https://discuss.ocaml.org/u/nojb)\ **Post date:** [January 11, 2024, 7:20pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/6 "2024-01-11T19:20:55Z")
> [@lukstafi](#): > > I managed to get ocamlobjinfo ==\> `Extra C options: -lgccjit -Wl,-export-dynamic`, but it did not help. I think you need to get `-lgccjit` inside the “Extra dynamically-loaded libraries” field of your archive. This is typically achieved by passing `-lgccjit` to the `ocamlmklib` invocation. Cheers, Nicolas ---
**Author:** ![lukstafi](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lukstafi/32/3442_2.png) [@lukstafi](https://discuss.ocaml.org/u/lukstafi)\ **Post date:** [January 11, 2024, 7:29pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/7 "2024-01-11T19:29:58Z")
Yes but does it mean I need to abandon the `ctypes` stanza? Since I wasn’t able to achieve passing arguments to `ocamlmklib`. Edit: despite this line, meaning it should be possible, maybe outside of the `ctypes` stanza: [dune/src/dune\_rules/lib\_rules.ml at e515c294686999610e14079608a7d912c77bfe1b · ocaml/dune · GitHub](https://github.com/ocaml/dune/blob/e515c294686999610e14079608a7d912c77bfe1b/src/dune_rules/lib_rules.ml#L202) ---
**Author:** ![nojb](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/nojb/32/519_2.png) [@nojb](https://discuss.ocaml.org/u/nojb)\ **Post date:** [January 11, 2024, 7:33pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/8 "2024-01-11T19:33:39Z")
> [@lukstafi](#): > > Yes but does it mean I need to abandon the `ctypes` stanza? I don’t know enough about the `ctypes` stanza to answer this question, sorry. > Did you try adding `(c_library_flags -lgccjit)` directly to the `(library)` stanza? Cheers, Nicolas ---
**Author:** ![lukstafi](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lukstafi/32/3442_2.png) [@lukstafi](https://discuss.ocaml.org/u/lukstafi)\ **Post date:** [January 11, 2024, 7:37pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/9 "2024-01-11T19:37:25Z")
> [@nojb](#): > > Did you try adding `(c_library_flags -lgccjit)` directly to the `(library)` stanza? Yes IIRC. (Double-checked now it doesn’t help.) I definitely also tried `(flags -cclib -lgccjit)`. And also global env `c_flags` and `flags`. ---
**Author:** ![soya](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/soya/32/119_2.png) [@soya](https://discuss.ocaml.org/u/soya)\ **Post date:** [January 11, 2024, 9:05pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/10 "2024-01-11T21:05:43Z")
> > > Add link flags for external dependencies when using ctypes. > > Required when t…he external lib is not statically linked, in which case > linker needs to be aware at runtime what libs to call. This is the case > for > > - dune exec \.bc > - dune utop > - mdx tests > > That is add to ocamlmklib, link flags such as -l\ -L\ > from ctypes if info is available. > > If dependent library are not installed in expected locations, env > variable such as LD\_LIBRARY\_PATH must be extended when required program > is run, depending on os. This may be fixed by adding relocatable paths to > link flags. This might help, had similar issue with ctypes and dune when using bytecode. ---
**Author:** ![lukstafi](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lukstafi/32/3442_2.png) [@lukstafi](https://discuss.ocaml.org/u/lukstafi)\ **Post date:** [January 11, 2024, 9:23pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/11 "2024-01-11T21:23:39Z")
Thanks, I haven’t seen this in my searches! In the meantime, I had another idea to try: generate/vendor `libgccjit.pc` and use `(build_flags_resolver pkg_config)`. If it doesn’t work, I’ll study this PR. Edit: ah, sorry I did see this. I linked this PR in my original post! ---
**Author:** ![lukstafi](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lukstafi/32/3442_2.png) [@lukstafi](https://discuss.ocaml.org/u/lukstafi)\ **Post date:** [January 11, 2024, 10:58pm UTC](https://discuss.ocaml.org/t/writing-ctypes-bindings-to-system-shared-libraries-for-bytecode-targets-via-the-dune-ctypes-stanza/13844/12 "2024-01-11T22:58:23Z")
I now converted to `(build_flags_resolver pkg_config)`, but the situation is the same: `ocamlmklib` still does not get any arguments (in particular it does not ask to link the `external_library_name`), and the execution still fails with the original error message. Edit (updated): I now patched [Add link flags ocamlmklib when using ctypes stubs. by frejsoya](https://github.com/ocaml/dune/pull/8784), and it solves the problem (both the `(build_flags_resolver pkg_config)` variant and the `(build_flags_resolver (vendored ...))` variant). It still has the [bytecode + c stubs not working as expected · Issue #108](https://github.com/ocaml/dune/issues/108) problem when `dune clean; dune exec` – but it is easily solved by `dune build; dune exec`; alternatively need to update `CAML_LD_LIBRARY_PATH` i.e. `dune clean; CAML_LD_LIBRARY_PATH=... dune exec` works, but using `(env (_ (env-vars (CAML_LD_LIBRARY_PATH ...))))` does not work.