Comment author: administrator

Dear Norman,

A large program compiled with ocamlc segfaults. I know that a program
compiled with ocamlopt can segfault if it runs out of stack, but I
believe this is not supposed to be possible with ocamlc.
[...]
#0 0x0805f57b in alloc_channel ()
#1 0x0805f626 in caml_out_channels_list ()
#2 0x08067566 in interprete ()
#3 0x080686a1 in caml_main ()
#4 0x0805ad1c in main ()
#5 0x400e6a51 in __libc_start_main () from /lib/libc.so.6
(gdb)

This looks interesting -- alloc_channel isn't a place where I would
have expected a crash :-)

Please let me know how I can provide more information that might help
you (or me) diagnose and repair this problem.

If you could send me a self-contained program that reproduces the
crash, I'll be happy to investigate.

• Xavier

Comment author: administrator

Dear Norman,

A large program compiled with ocamlc segfaults. I know that a program
compiled with ocamlopt can segfault if it runs out of stack, but I
believe this is not supposed to be possible with ocamlc.
#0 0x0805f57b in alloc_channel ()
#1 0x0805f626 in caml_out_channels_list ()
#2 0x08067566 in interprete ()

Thanks for the nicely packaged sources. I was able to reproduce the
crash easily, and understand it after a bit more effort. It turns out to
be a genuine bug in alloc_channel due to concurrent finalization and
reallocation of an I/O channel. A patch is included below. It is
against 3.07beta1 but I think it should apply cleanly to 3.06.

Best,

• Xavier

Index: csl/byterun/io.c
diff -c csl/byterun/io.c:1.62 csl/byterun/io.c:1.63
*** csl/byterun/io.c:1.62 Mon Jan 6 11:59:07 2003
--- csl/byterun/io.c Tue Jul 29 13:48:34 2003

*** 430,439 ****

CAMLexport value alloc_channel(struct channel *chan)
{
! value res = alloc_custom(&channel_operations, sizeof(struct channel *),
! 1, 1000);
Channel(res) = chan;

• chan->refcount++;
  return res;
  }

--- 430,439 ----

CAMLexport value alloc_channel(struct channel chan)
{
! value res;
! chan->refcount++; / prevent finalization during next alloc */
! res = alloc_custom(&channel_operations, sizeof(struct channel *), 1, 1000);
Channel(res) = chan;
return res;
}

Comment author: administrator

Fixed 2003-07-29 by XL