[Caml-list] Segmentationfault on 64bit when called from C

[Georg Martius <georg.martius@web.de>]

Dear all,

I experienced a very intricate bug in the 64bit runtime that took me some days 
to nail down. I submitted a bug report #5707. 
Here is what I found: When ocaml code is compiled as as a libary and called 
from C++ under 64bit I get a broken stack for functions with more than 8 
parameters. I compiled ocaml 3.12.1 version with -fPIC. BTW: everthing works 
fine on 32bit.

The problem occurs when a function with more than 8 parameters is called. The 
last parameters do have the right value. If afterwards a reference is accessed 
then a segmentation fault occurs, see the code below.

Here the code: (in the bug report I also attached a tar file)
---- m1.ml ------------------
module M2 = struct
  let v      = ref 0;;

  let foo p1 p2 p3 p4 p5 p6 p7 p8 p9 =
    prerr_endline "start";
    print_endline (string_of_int p1);
    print_endline (string_of_int p2);
    print_endline (string_of_int p3);
    print_endline (string_of_int p4);
    print_endline (string_of_int p5);
    print_endline (string_of_int p6);
    print_endline (string_of_int p7);
    print_endline (string_of_int p8);
    print_endline (string_of_int p9);
    print_endline (string_of_int !v);
    prerr_endline "end";
  ;;
end;;


let test i : unit =
  print_endline ("Initialising: " ^ (string_of_int i));
  M2.foo 1 2 3 4 5 6 7 8 9;
;;

(* test 10;;*)

let _ = Callback.register "test"         test;;
----- end m1.ml

----- interface.c
#include <caml/mlvalues.h>
#include <caml/callback.h>

#include "interface.h"

void ocaml_initialize(char** argv){
  caml_main(argv);
}

void ocaml_test(){
  value* test_pointer = caml_named_value("test");
  caml_callback(*test_pointer, Val_int(11));
}
------ end interface.c

----- interface.h
void ocaml_initialize(char** argv);

void ocaml_test();
----- end interface.h

You need ocaml to be compiled with -fPIC on order to be able to generate a 
shared libary on 64bit, as written in the INSTALL
./configure -cc "gcc -fPIC" -aspp "gcc -c -fPIC"

ocamlopt -o libmytest.so -ccopt -shared interface.c m1.ml
g++ -Wall main.cpp  -lmytest -o test
./test
---- output:
Initialising: 11
start
1
2
3
4
5
6
7
8
70367718054944
Segmentation fault (core dumped)
--- end outpuyt

Some Observations:
Calling it natively as an ocaml executable works.
Commenting the access to !v removes the segmentation fault but still the 
values are wrong.
Uncommenting line "test 10", causes the error already at this call and the 
subsequent call from C runs fine!

Best regards,
  Georg