Original bug ID: 3740
Reporter: administrator
Status: closed (set by @xavierleroy on 2006-06-17T10:45:36Z)
Resolution: unable to duplicate
Priority: normal
Severity: minor
Category: ~DO NOT USE (was: OCaml general)

Bug description

Full_Name: Florian Hars
Version: 3.08.3 (from godi)
OS: linux/amd64
Submission from: dialin-145-254-038-023.arcor-ip.net (145.254.38.23)

These things always happen on the last day before the vacation, when
the prototype must definitely work and you have no time to find a
minimal example...

I am writing a cgi program, which contains code like the following
(only more complicated, ix is really a struct containing among other
things a Netcgi.cgi_activation and a Postgresql.connection. cols
contains records, not just simple strings and table
has far more fields (16)). Parts use the same function in place of the
do_something in the example (camlTable__save_show in the backtrace
below) with different tables. All parts have worked during various
stages of development, some work even now, but in some places I get a
segfault after the program writes AA to stderr.

type table = {
txt: string;
do_it: int -> string -> unit;
cols: string array;
}

let do_something t ix s =
prerr_endline "AA";
let n = Array.length t.cols in
prerr_endline "BB";
Printf.printf "%s\n" t.txt;
for i = 0 to n - 1 do
Printf.printf "%d %d %s %s\n" ix i t.cols.(i) s
done

let rec t0 = {
txt = "Foo";
do_it = (fun ix s -> do_something t0 ix s);
cols = [| "a"; "b"; "c" |];
}

let rec t = {
t0 with
do_it = (fun ix s -> do_something t ix s);
cols = [| "A"; "B";|];
}

let _ =
t.do_it 1 "s"

Here is a part of the apache logfile I get if I wrap my program in a
skript that calls it through gdb -batch:

AA

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 182915746208 (LWP 11161)]
0x0000000000419434 in camlTable__save_391 ()
#0 0x0000000000419434 in camlTable__save_391 ()
#1 0x0000000000000000 in ?? ()
#2 0x00000000004d2b74 in caml_flush ()
#3 0x00000000004d338e in caml_ml_flush ()
#4 0x0000000000000000 in ?? ()
#5 0x0000002a96a4c980 in ?? ()
#6 0x0000000000419743 in camlTable__save_show_403 ()
#7 0x0000002a96a4b2c0 in ?? ()
#8 0x0000000000000000 in ?? ()
#9 0x0000002a96a4c980 in ?? ()

Same thing if I compile to bytecode:

AA

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 182917156976 (LWP 11770)]
0x0000000000428b28 in caml_interprete ()
#0 0x0000000000428b28 in caml_interprete ()
#1 0x000000000042a772 in caml_main ()
#2 0x000000000041a268 in main ()

In one case, the working version is

let rec table' = {
table with
save = (fun rq x_id -> save_user {table with cols=cols'} rq x_id);
}

while this segfaults:

let rec table' = {
table with
save = (fun rq x_id -> save_user table' rq x_id);
cols=cols'
}

I can live with the extra allocation on every invocation of
table'.save to get things running, but it is a bit annoying.