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Building with OCamlMkLib
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Date: 2009-01-20 (17:03)
From: John Whitington <john@c...>
Subject: Building with OCamlMkLib
Hi Folks,

I'm building a Plain C interface to our PDF libraries, but am stuck.  
The idea is to build a library with Ocamlmklib containing the C  
wrapper around the ocaml code.

I've used some test files (included below) in place of the real ones.

I can successfully build the library (I'm using OS x / intel):

ocamlc -c -cc "cc" -ccopt " -DNATIVE_CODE -o cpdflibwrapper.o"  
ocamlc cpdflibc.mli
ocamlc cpdflibc.ml
ocamlmklib -o camlpdfc cpdflibc.ml cpdflibwrapper.a

(builds dllcamlpdfc.so, camlpdfc.a, camlpdfc.cma, camlpdfc.cmxa)

But trying to link a C program which uses the new library fails. Do I  
need to include something else, or have I got the ocamlmklib stage  

feast:trunk john$ gcc test.c -o test_executable -L. -L/usr/local/lib/ 
ocaml -lcamlpdfc -lasmrun
Undefined symbols:
   "_caml_code_area_end", referenced from:
       _caml_code_area_end$non_lazy_ptr in libasmrun.a(signals_asm.o)
       _caml_code_area_end$non_lazy_ptr in libasmrun.a(intern.o)
       _caml_code_area_end$non_lazy_ptr in libasmrun.a(extern.o)
   "_caml_program", referenced from:
       _caml_start_program in libasmrun.a(i386.o)
   "_caml_bucket_Out_of_memory", referenced from:
       _caml_bucket_Out_of_memory$non_lazy_ptr in libasmrun.a(fail.o)

(many more lines)

Here are the input files forming the mixed ocaml/c library:

(* cpdflibc.mli *)
val twice : int -> int

(* cpdflibc.ml *)
let twice x = x * 2

/* cpdflibwrapper.h */
int twice (int);

/* cpdflibwrapper.c */
#include <stdio.h>
#include <caml/memory.h>
#include <caml/callback.h>

int twice_c (int i)
   CAMLlocal1 (result);
   result = caml_callback(*caml_named_value("twice"), Val_int(i));

And here's the C program which will be using the libary:

/* test.c */
#include <stdio.h>
#include "cpdflibwrapper.h"

int main ()
   printf("Twice two is %i\n", twice_c(2));

Here's a zip containing those files: http://www.coherentpdf.com/files.zip

Any ideas?

John Whitington
Coherent Graphics Ltd