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

[Gerd Stolpmann <info@gerd-stolpmann.de>]

Just a rough guess: The frametable is not initialized. Quite funny that
it crashes so quickly. (Maybe more is not initialized, maybe the heap
register, so it crashes at the first allocation.)

You cannot just link Ocaml code without adding the frametable. This is a
description of how the stack and the CPU registers are used at runtime.
If it is missing the OCaml runtime thinks that the Ocaml code is C code,
and applies the wrong conventions.

The -shared switch generates a library that is prepared to be loaded
with Dynlink. Dynlink registers the frametable.

You should consider using -output-obj to create a library that can be
loaded without such tricks (see section 18.7.5 of the Ocaml manual).

Gerd

Am Dienstag, den 31.07.2012, 14:17 +0200 schrieb Georg Martius:
> 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
> 
> 

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