次のようにすると core を吐きます。

% ./ruby -e '
str = "a" * 0x20000
r, w = IO.pipe
Thread.new { Thread.pass
  w << "a" * 4096
  str.replace ""
  w.close
}
p r.read(nil, str)
'
-e:9: [BUG] Segmentation fault
ruby 1.9.0 (2004-10-11) [i686-linux]

zsh: abort (core dumped)  ./ruby -e 
% gdb ruby core 
GNU gdb 6.1-debian
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-linux"...Using host libthread_db library "/lib/libthread_db.so.1".

Core was generated by `./ruby -e 
str = "a" * 0x20000
r, w = IO.pipe
Thread.new { Thread.pass
  w << "'.
Program terminated with signal 6, Aborted.
Reading symbols from /lib/libdl.so.2...done.
Loaded symbols for /lib/libdl.so.2
Reading symbols from /lib/libcrypt.so.1...done.
Loaded symbols for /lib/libcrypt.so.1
Reading symbols from /lib/libm.so.6...done.
Loaded symbols for /lib/libm.so.6
Reading symbols from /lib/libc.so.6...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib/ld-linux.so.2...done.
Loaded symbols for /lib/ld-linux.so.2
#0  0x4009e741 in kill () from /lib/libc.so.6
(gdb) bt
#0  0x4009e741 in kill () from /lib/libc.so.6
#1  0x4009e4c5 in raise () from /lib/libc.so.6
#2  0x4009fa08 in abort () from /lib/libc.so.6
#3  0x080d2456 in rb_bug (fmt=0x0) at error.c:214
#4  0x080b0392 in sigsegv (sig=11) at signal.c:446
#5  <signal handler called>
#6  0x08076239 in rb_io_fread (ptr=0x401da008 <Address 0x401da008 out of bounds>, len=8192, f=0x8139f88) at io.c:968
#7  0x080763ad in read_all (fptr=0x8139f60, siz=8192, str=1075607756) at io.c:1028
#8  0x0807688b in io_read (argc=0, argv=0x0, io=0) at io.c:1182
#9  0x08069f5a in call_cfunc (func=0x8076690 <io_read>, recv=1075607736, len=1075683336, argc=135503752, argv=0xbfffead8)
    at eval.c:5367
#10 0x0805e167 in rb_call0 (klass=1075636676, recv=1075607736, id=7329, oid=0, argc=2, argv=0xbfffead8, body=0x401ce44c, 
    nosuper=0) at eval.c:5508
#11 0x0805e418 in rb_call (klass=1075636676, recv=1075607736, mid=7329, argc=2, argv=0xbfffead8, scope=0) at eval.c:5729
#12 0x08059348 in rb_eval (self=1075673496, n=0x0) at ruby.h:635
#13 0x08059678 in rb_eval (self=1075673496, n=0x0) at ruby.h:664
#14 0x080558db in ruby_exec () at eval.c:1458
#15 0x08055920 in ruby_run () at eval.c:1484
#16 0x080539e5 in main (argc=0, argv=0x0, envp=0xbffff904) at main.c:38
(gdb) 
-- 
[田中 哲][たなか あきら][Tanaka Akira]