OCaml shared lib for another shared lib - c

Question

I am exploring some adventurous ideas.
TL:DR; gnumake is able to use loadable modules, I am trying to use that C barrier to use OCaml but have trouble with the OCaml runtime initializing.
I have this OCaml code:
(* This is speak_ocaml.ml *)
let do_speak () =
print_endline "This called from OCaml!!";
flush stdout;
"Some return value from OCaml"
let () =
Callback.register "speak" do_speak
and I also have this C code: (Yes, needs to use extra CAML macros but not relevant here)
#include <stdlib.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <gnumake.h>
#include <caml/mlvalues.h>
#include <caml/callback.h>
#include <caml/memory.h>
#include <caml/alloc.h>
int plugin_is_GPL_compatible;
char *ocaml_speaker(const char *func_name, int argc, char **argv)
{
char *answer =
String_val(caml_callback(*caml_named_value("speak"), Val_unit));
printf("Speaking and got: %s\n", answer);
char *buf = gmk_alloc(strlen(answer) + 1);
strcpy(buf, answer);
/* receive_arg */
return buf;
}
int do_speak_gmk_setup()
{
printf("Getting Called by Make\n");
// This is pretty critical, will explain below
char **argv = {"/home/Edgar/foo", NULL};
caml_startup(argv);
printf("Called caml_startup\n");
gmk_add_function("speak", ocaml_speaker, 1, (unsigned int)1, 1);
return 1;
}
and I'm compiling it with this Makefile
all:
ocamlopt -c speak_ocaml.ml
ocamlopt -output-obj -o caml_code.o speak_ocaml.cmx
clang -I`ocamlc -where` -c do_speak.c -o do_speak.o
clang -shared -undefined dynamic_lookup -fPIC -L`ocamlc -where` -ldl \
-lasmrun do_speak.o caml_code.o -o do_speak.so
show_off:
echo "Speaker?"
${speak 123}
clean:
#rm -rf *.{cmi,cmt,cmi,cmx,o,cmo,so}
And my problem is that only printf("Getting Called by Make\n"); is going off when I add the appropriate load do_speak.so in the Makefile, caml_startup is not going off correctly. Now I am calling caml_startup because if I don't then I get an error of
Makefile:9: dlopen(do_speak.so, 9): Symbol not found: _caml_atom_table
Referenced from: do_speak.so
Expected in: flat namespace
in do_speak.so
Makefile:9: *** do_speak.so: failed to load. Stop.
And this is because of the way that clang on OS X does linking, see here for more details: http://psellos.com/2014/10/2014.10.atom-table-undef.html
I am kind of out of ideas... I need to create a C shared library out of OCaml code which then needs to be part of another C shared library from which I obviously don't have the original argv pointers that caml_startup wants. As my code sample show, I've tried faking it out, and also used caml_startup(NULL) and char **argv = {NULL}; caml_startup(argv) with similar lack of success. I don't know how else to initialize the runtime correctly.

Answer 1

I actually can't tell very well what you're asking. However, here's a comment on this part of your question:
I've tried faking it out, and also used caml_startup(NULL) and char **argv = {NULL}; caml_startup(argv) with similar lack of success. I don't know how else to initialize the runtime correctly.
As far as I know, the only reason for the argv argument of caml_startup is to establish the command-line arguments (for Sys.argv). If you don't need command-line arguments it should be OK to call like this:
char *arg = NULL;
caml_startup(&arg);
Technically argv is supposed to contain at least one string (the name of the program). So maybe it would be better to call like this:
char *argv[] = { "program", NULL };
caml_startup(argv);