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To: caml-list@inria.fr
Subject: Re: [Caml-list] Hybrid ML/C programs and exceptions
References: <200204112133.OAA05135@gnp.com>
From: Remi VANICAT <vanicat@labri.u-bordeaux.fr>
Date: 12 Apr 2002 01:25:46 +0200
In-Reply-To: <200204112133.OAA05135@gnp.com>
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Tom Buscher <tbuscher@gnp.com> writes:

> 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;
> }

this seem suspicious, CAMLprim should have type

CAMLprim value foo(value)

CAMLreturn0 is only usefull in the case of something like

ML call C witch call C witch call ML

(for example it useful for Gtk binding, where there are C callback
which then call ML).

by the way, changing foo.c with :

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

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

doesn't change the problem...

-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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