Segfault with close_out in ocaml 3.09.2

Segfault with close_out in ocaml 3.09.2

[Jørgen Hermanrud Fjeld]

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Hi!
I can provoke a segfault with close_out, and suspect a bug somewhere in
ocaml 3.09.2 or the Pervasives module of ocaml 3.09.2, as shipping with 
Ubuntu feisty.

To reproduce, save the attached files, use ocaml 3.09.2 and run
####
ocamlopt unix.cmxa -o nosegfault nosegfault.ml
ocamlopt unix.cmxa -o segfault segfault.ml
./nosegfault ; ./segfault
####

The difference between segfault.ml and nosegfault.ml is the allocation 
of a large string
####
let _ = String.create (Sys.max_string_length) in
####

The bug appears for the second call to close_out.

When I use Unix.close, there is no problem.

The original code where the testcase is derived form ran fine when
compiled with ocaml 3.08.

When I use ocaml 3.10.0 the problem is gone.

If someone can help discover why the segfault appears that would be
nice.
Since the bug disappears in ocaml 3.10, the bug is probably fixed, 
which one can check when the cause of the segfault is discovered.


-- 
Sincerely | Homepage:
Jørgen    | http://www.hex.no/jhf
          | Public GPG key:
          | http://www.hex.no/jhf/key.txt



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let run closer command = 
  let (from_command,to_command) = Unix.open_process command in
    closer to_command ;
    try while true do 
          print_endline (input_line from_command) ;
        done
    with End_of_file -> () ;
    ignore (Unix.close_process (from_command,to_command)) ;;

let _ = String.create (Sys.max_string_length) in
run (fun to_command -> Unix.close (Unix.descr_of_out_channel to_command)) "echo 1" ;
run (fun to_command -> Unix.close (Unix.descr_of_out_channel to_command)) "echo 2" ;
run (fun to_command -> close_out to_command)                              "echo 3" ;
run (fun to_command -> close_out to_command)                              "echo 4" ;

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let run closer command = 
  let (from_command,to_command) = Unix.open_process command in
    closer to_command ;
    try while true do 
          print_endline (input_line from_command) ;
        done
    with End_of_file -> () ;
    ignore (Unix.close_process (from_command,to_command)) ;;

run (fun to_command -> Unix.close (Unix.descr_of_out_channel to_command)) "echo 1" ;
run (fun to_command -> Unix.close (Unix.descr_of_out_channel to_command)) "echo 2" ;
run (fun to_command -> close_out to_command)                              "echo 3" ;
run (fun to_command -> close_out to_command)                              "echo 4" ;

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Re: [Caml-list] Segfault with close_out in ocaml 3.09.2

[Martin Jambon]

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On Sun, 1 Jul 2007, Jørgen Hermanrud Fjeld wrote:

> Hi!
> I can provoke a segfault with close_out, and suspect a bug somewhere in
> ocaml 3.09.2 or the Pervasives module of ocaml 3.09.2, as shipping with
> Ubuntu feisty.

It's probably this bug:

http://caml.inria.fr/mantis/view.php?id=4039

Martin

>
> To reproduce, save the attached files, use ocaml 3.09.2 and run
> ####
> ocamlopt unix.cmxa -o nosegfault nosegfault.ml
> ocamlopt unix.cmxa -o segfault segfault.ml
> ./nosegfault ; ./segfault
> ####
>
> The difference between segfault.ml and nosegfault.ml is the allocation
> of a large string
> ####
> let _ = String.create (Sys.max_string_length) in
> ####
>
> The bug appears for the second call to close_out.
>
> When I use Unix.close, there is no problem.
>
> The original code where the testcase is derived form ran fine when
> compiled with ocaml 3.08.
>
> When I use ocaml 3.10.0 the problem is gone.
>
> If someone can help discover why the segfault appears that would be
> nice.
> Since the bug disappears in ocaml 3.10, the bug is probably fixed,
> which one can check when the cause of the segfault is discovered.
>
>
> -- 
> Sincerely | Homepage:
> Jørgen    | http://www.hex.no/jhf
>          | Public GPG key:
>          | http://www.hex.no/jhf/key.txt
>
>
>