toplevel not executed: Bug ?

toplevel not executed: Bug ?

[Romain Beauxis]

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	Hi all !

I've encountered a strange bug while preparing a caml module with C function. 
Depending on the execution of a caml-defined function, the toplevel is 
evaluated or not, leading to a segfault when calling a caml callback from C.

The code of the C part is:
<---
#include <caml/callback.h>
#include <caml/custom.h>
#include <caml/memory.h>

CAMLprim value f(unit)
{
  CAMLparam0();
  caml_callback(*caml_named_value("test_printf"),Val_unit);
  CAMLreturn(Val_unit);
}
<---

The code of the caml part is:
<---
let f () = Printf.printf "blalba\n"; flush_all ()

let () = Callback.register "test_printf" f

module Test=
struct

  external f : unit -> unit = "f"

  let f2 () = Printf.printf "f2\n"; flush_all ()

end
<---

The code that uses the module is:
<---
(* This needs to be executed *)
let () = Test.Test.f2 ()

let () = Test.Test.f ()
<---

Step to reproduce:
Compile all using the following sequence:
gcc -c -o test_stubs.o ./test_stubs.c -fPIC
ocamlmklib -o test_stubs ./test_stubs.o
ocamlopt -c test.ml
ocamlopt -a -cclib -ltest_stubs -o test.cmxa test.cmx
ocamlopt -c bla.ml
ocamlopt -I . test.cmxa bla.cmx -o bla

Then, if you comment the first call to f2 in bla.ml, then the toplevel is not 
evaluated before executing the C function, leading to a segfault..

Is this a bug or am I missing something ?

Romain

PS: files attached

[-- Attachment #2: bla.ml --]
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(* This needs to be executed *)
let () = Test.Test.f2 ()

let () = Test.Test.f ()


[-- Attachment #3: test.ml --]
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let f () = Printf.printf "blalba\n"; flush_all ()

let () = Callback.register "test_printf" f

module Test=
struct

  external f : unit -> unit = "f"

  let f2 () = Printf.printf "f2\n"; flush_all () 

end


[-- Attachment #4: test_stubs.c --]
[-- Type: text/x-csrc, Size: 208 bytes --]



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

CAMLprim value f(unit)
{
  CAMLparam0();
  caml_callback(*caml_named_value("test_printf"),Val_unit);
  CAMLreturn(Val_unit);
}

Re: [Caml-list] toplevel not executed: Bug ?

[Stéphane Glondu]

Romain Beauxis wrote:
> I've encountered a strange bug while preparing a caml module with C function. 
> Depending on the execution of a caml-defined function, the toplevel is 
> evaluated or not, leading to a segfault when calling a caml callback from C.
> [...]

I don't know whether this is a bug, but I have an explanation.

At linking phase, module Test is not linked in because it is not used.
When you use "-linkall", the segfault disappear.

Module Test is considered unused because the inferred interface for
module Test records that f is an external. You can force the usage of
module Test by providing your own .mli, where f is abstracted. When you
do so, the segfault disappear (even without -linkall).


HTH,

-- 
Stéphane Glondu