Interface C and Caml

Interface C and Caml

[David LONY]

Hi all,

I'm trying to interface Ocaml with C code. But unfortunately I don't 
know why it doesn't work well...
This is my caml code (truc.ml) :

let test_char a = a+1
let _ = Callback.register "caml_test_char" test_char;;

and this is my C code (test.c) :

#include <stdio.h>
#include <caml/mlvalues.h>
#include <caml/callback.h>

int test_char(int n)
{
  static value * test_char_closure = NULL;
  if (test_char_closure == NULL)
        {
        test_char_closure = caml_named_value("caml_test_char");
        }
  return Int_val(caml_callback(*test_char_closure, Val_int(n)));
}

int main(int argc, char ** argv)
{
  int result;
  caml_startup(argv);
  result = test_char(10);
  printf("%d\n", result);
  return 0;
}

I obtain the final executable by typing this command :
ocamlopt -cc "gcc" -o test truc.ml test.c

But if I try to do the same thing by typing :

ocamlopt -output-obj truc.ml -o truc.o
gcc -c test.c
gcc -o test test.o truc.o -L/usr/lib/ocaml/3.09.2 -lasmrun

I obtain :

truc.o: In function `caml_program':
(.text+0xd): undefined reference to `camlTruc__entry'
truc.o: In function `caml_globals':
(.data+0x1b4): undefined reference to `camlTruc'
truc.o: In function `caml_data_segments':
(.data+0x21c): undefined reference to `camlTruc__data_begin'
truc.o: In function `caml_data_segments':
(.data+0x220): undefined reference to `camlTruc__data_end'
truc.o: In function `caml_code_segments':
----BLABLA
/usr/lib/ocaml/3.09.2/libasmrun.a(floats.o): In function `caml_atan_float':
----BLABLA
/usr/lib/ocaml/3.09.2/libasmrun.a(floats.o): In function `caml_power_float':
(.text+0x380): undefined reference to `pow'
/usr/lib/ocaml/3.09.2/libasmrun.a(floats.o): In function `caml_sqrt_float':
(.text+0x3b1): undefined reference to `sqrt'
/usr/lib/ocaml/3.09.2/libasmrun.a(floats.o): In function `caml_log10_float':
(.text+0x492): undefined reference to `log10'
/usr/lib/ocaml/3.09.2/libasmrun.a(floats.o): In function `caml_log_float':
/usr/lib/ocaml/3.09.2/libasmrun.a(unix.o): In function `caml_dlclose':
----BLABLA

What is wrong ? Does anyone has the same problem ?

Regards
David LONY

Re: [Caml-list] Interface C and Caml

[Alain Frisch]

David LONY wrote:
> ocamlopt -output-obj truc.ml -o truc.o
> gcc -c test.c
> gcc -o test test.o truc.o -L/usr/lib/ocaml/3.09.2 -lasmrun

Two problems here:

1. the first line first compiles truc.ml into truc.cmx/truc.o as usual, 
and then combine truc.o with stdlib.a and a temporary startup object 
into truc.o. It seems that the linker first creates a fresh truc.o file 
before reading the existing truc.o, so the native code produced by the 
compiler is actually lost. You should use a different file name:

ocamlopt -output-obj truc.ml -o truc_main.o


2. the last line should mention the -lm and -ldl libraries, as can be 
found by:

   grep NATIVECCLIBS `ocamlc -where`/Makefile.config

So:

gcc -o test test.o truc_main.o -L/usr/lib/ocaml/3.09.2 -lasmrun -lm -ldl

-- Alain

Re: [Caml-list] Interface C and Caml

[David LONY]

It work well!!
Thanks a lot Alain

David


Alain Frisch a écrit :
> David LONY wrote:
>> ocamlopt -output-obj truc.ml -o truc.o
>> gcc -c test.c
>> gcc -o test test.o truc.o -L/usr/lib/ocaml/3.09.2 -lasmrun
>
> Two problems here:
>
> 1. the first line first compiles truc.ml into truc.cmx/truc.o as 
> usual, and then combine truc.o with stdlib.a and a temporary startup 
> object into truc.o. It seems that the linker first creates a fresh 
> truc.o file before reading the existing truc.o, so the native code 
> produced by the compiler is actually lost. You should use a different 
> file name:
>
> ocamlopt -output-obj truc.ml -o truc_main.o
>
>
> 2. the last line should mention the -lm and -ldl libraries, as can be 
> found by:
>
>   grep NATIVECCLIBS `ocamlc -where`/Makefile.config
>
> So:
>
> gcc -o test test.o truc_main.o -L/usr/lib/ocaml/3.09.2 -lasmrun -lm -ldl
>
> -- Alain
>
>