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Using ocamlbuild to generate dynamic libraries (*.so/*.dll) with a C-API and an OCaml implementation? #6918

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vicuna opened this Issue Jun 26, 2015 · 4 comments

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vicuna commented Jun 26, 2015

Original bug ID: 6918
Reporter: sawfish
Status: resolved (set by @damiendoligez on 2017-03-01T12:18:19Z)
Resolution: suspended
Priority: normal
Severity: feature
Version: 4.02.2
Target version: later
Category: -for ocamlbuild use https://github.com/ocaml/ocamlbuild/issues
Tags: patch
Related to: #6733 #6797
Monitored by: @whitequark @dbuenzli

Bug description

Could we enable ocamlbuild to build dynamic libraries (.so/.dll)
that are accessible via a C-API which internally uses OCaml code?

We have such a setup, where we need to provide a C-API to the outside
and use OCaml to implement the functionality.

The request is somehow the reverse of the C-stubs build:
We are not looking for a means to build stubs to C-libraries,
but to wrap OCaml code into a C-API.

Additional information

The custom myocamlbuild.ml (admittedly hacked and ugly) that does the job for our setup in Windows is as follows:

open Ocamlbuild_plugin
open Command

(** This function implements the action for building the native C library *)
let library_build env (_build : builder) =
let lib_main = env "%.cmxa" in
let stub_obj = env "%_api.obj" in
let final_link_cmd = Cmd (S [ S[A "ocamlfind"; A "ocamlopt";
S[A "-package"; A "ocamlgraph"];
S[A "-package"; A "batteries"];
S[A "-cclib"; A "-implib"];
S[A "-cclib"; A "-maindll"];
A "-output-obj"; A "-linkpkg"; A "-linkall"]; S [A "-o"; A "ourlibrary.dll"]; P stub_obj; P lib_main]) in
let pn_lib_main = Pathname.mk lib_main in
let pn_stub_main = Pathname.mk stub_obj in
let _ = _build [[pn_lib_main]; [pn_stub_main]] in
final_link_cmd

let () =
dispatch (function
| After_rules ->
rule "Building C-DLL from OCaml with a C-API"
~prod:"%.clibrary"
~deps:["%.ml"; "%_api.c"; "%.h"]
library_build;
flag ["clibrary"] (A "-linkpkg");
tag_file "</.so>" ["clibrary"]
| _ -> ())

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vicuna commented Jul 19, 2015

Comment author: @whitequark

This is already done. See PR6733 and PR6797.

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vicuna commented Jul 23, 2015

Comment author: sawfish

PR6733 and PR6797 address parts of the issue I was reporting.
However, we additionally miss a way to tell ocamlbuild to compile specific *.c files and link the resulting object code into the final .dll/.so

The background is as follows:
We use C to implement an API that wraps the OCaml core of our library.
Is there a possibility to make ocamlbuild compile and link the
additional C files that contain the wrapper code?
An approach that is similar to the *.clib files that are used for compiling C-stubs would be great.

However, perhaps I overlook something and such a build configuration
becomes available due to PR6733 and PR6797?

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vicuna commented Jul 23, 2015

Comment author: @whitequark

No, that is not available.

I think having an additional rule .clib -> .{dll,so,dylib} would be valuable. You could put a .native.o inside that library.

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vicuna commented Mar 1, 2017

Comment author: @damiendoligez

ocamlbuild is now a separate project that lives on GitHub.
PR transferred to ocaml/ocamlbuild#184

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