(* Step 5b: OCaml 5.2 installs its SIGSEGV handler per-domain, not once at
   startup, so "read the disposition after caml_startup" is not the whole
   question. This asks it at four moments, and then asks the thing that
   actually matters: does Stack_overflow still get raised once the break loop
   has taken SIGSEGV? *)

external show : string -> unit = "spike_show_segv"
external take_segv : unit -> unit = "spike_take_segv"
external chain_segv : unit -> unit = "spike_chain_segv"
external sweep : unit -> unit = "spike_sweep"

let rec deep n = if n <= 0 then 0 else 1 + deep (n - 1) + (if n < 0 then deep n else 0)

let overflow_result () =
  try
    let n = deep 100_000_000 in
    Printf.sprintf "returned %d (no overflow)" n
  with Stack_overflow -> "Stack_overflow raised"

let () =
  show "at module init (main domain up)";
  let d = Domain.spawn (fun () -> show "inside a spawned domain") in
  Domain.join d;
  show "after Domain.join";
  print_endline "every signal the OCaml runtime is holding:";
  sweep ();
  Printf.sprintf "before touching SIGSEGV: %s" (overflow_result ()) |> print_endline;
  take_segv ();
  show "after the break loop takes SIGSEGV outright";
  Printf.sprintf "with SIGSEGV taken outright: %s" (overflow_result ())
  |> print_endline;
  chain_segv ();
  show "after the break loop chains to OCaml's handler";
  Printf.sprintf "with SIGSEGV chained: %s" (overflow_result ()) |> print_endline