[Caml-list] Hybrid ML/C programs and exceptions

[Tom Buscher <tbuscher@gnp.com>]

Hi,

We have a hybrid O'Caml/C application in which ML calls C,
which calls ML, like this:

  ML -> C -> ML
   1    2    3

The "lower" ML(3) raises an exception, which is dealt with
by C(2) using one of the callback_exn functions. When the C
function returns, the "upper" ML function generates a bus
error on Solaris 8, on writing to a mutable global variable.
We are using O'Caml 3.04 with the bytecode compiler.

Attached is a sample program of the same structure that
reproduces this problem. The problem appears to be caused by
the handling of the RAISE opcode in interprete(), executing
the "lower" ML bytecode. It sets extern_sp to a value which
reflects the program state before the C layer was called.

Is this program structure allowed?

Regards,

Tom, Trevor and Jeff

------------------------------------------------------------
FILE: top.ml
------------------------------------------------------------
exception Bot;;
let bot() = raise Bot 
let _ = Callback.register "bot" bot

external foo : unit -> unit = "foo"

let r = ref 1;;
r := 2;
foo();
r := 3

------------------------------------------------------------
FILE: foo.c
------------------------------------------------------------
#include <caml/mlvalues.h>
#include <caml/callback.h>
#include <caml/memory.h>

CAMLprim void
foo(value unit)
{
        CAMLparam1(unit);
        callback_exn(*caml_named_value("bot"), Val_int(0));
        CAMLreturn0;
}

------------------------------------------------------------
Build command (with gcc-2.95.3):

  ocamlc -custom -o top top.ml foo.c
------------------------------------------------------------
Tom Buscher                       "For every complex problem,
GNP Computers, Inc.                there is a simple solution.
tbuscher@gnp.com                   And it is wrong."
fon: +1 626.305.8484
fax: +1 626.599.3115                         -- H. L. Mencken
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