次のように core を吐くようです。

% ./ruby -e '
class A < Array
  private :concat
  def m
    concat []
  end
end
A.new.m
'
-e:9: [BUG] Segmentation fault
ruby 1.9.0 (2004-07-28) [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 
class A < Array
  private :concat
  def m
    concat []
  end
end
A.'.
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  0x4009d721 in kill () from /lib/libc.so.6
(gdb) bt
#0  0x4009d721 in kill () from /lib/libc.so.6
#1  0x4009d4c5 in raise () from /lib/libc.so.6
#2  0x4009e9e8 in abort () from /lib/libc.so.6
#3  0x080d0856 in rb_bug (fmt=0x0) at error.c:214
#4  0x080af0d2 in sigsegv (sig=11) at signal.c:446
#5  <signal handler called>
#6  call_cfunc (func=0x80c5280 <rb_ary_concat>, recv=1075604600, len=1, argc=1, argv=0x8) at eval.c:5389
#7  0x0805e177 in rb_call0 (klass=1075643680, recv=1075604600, id=4505, oid=3, argc=1, argv=0x8, body=0x401d0214, 
    nosuper=0) at eval.c:5523
#8  0x0805e428 in rb_call (klass=1075643680, recv=1075604600, mid=4505, argc=1, argv=0x8, scope=3) at eval.c:5744
#9  0x0805e9b1 in rb_call_super (argc=3, argv=0x3) at eval.c:5880
#10 0x080598b1 in rb_eval (self=1075604600, n=0x3) at eval.c:3273
#11 0x0805e267 in rb_call0 (klass=1075604660, recv=1075604600, id=4505, oid=3, argc=1, argv=0xbfffe978, body=0x401c6c50, 
    nosuper=0) at eval.c:5543
#12 0x0805e428 in rb_call (klass=1075604660, recv=1075604600, mid=4505, argc=1, argv=0xbfffe978, scope=1) at eval.c:5744
#13 0x08059372 in rb_eval (self=1075604600, n=0x3) at ruby.h:634
#14 0x0805dc8b in rb_call0 (klass=1075604660, recv=1075604600, id=10289, oid=3, argc=0, argv=0x0, body=0x401c6de0, 
    nosuper=0) at eval.c:5651
#15 0x0805e428 in rb_call (klass=1075604660, recv=1075604600, mid=10289, argc=0, argv=0x0, scope=0) at eval.c:5744
#16 0x08059372 in rb_eval (self=1075669400, n=0x3) at ruby.h:634
#17 0x0805586b in ruby_exec () at eval.c:1459
#18 0x080558b0 in ruby_run () at eval.c:1480
#19 0x08053985 in main (argc=3, argv=0x3, envp=0xbffff954) at main.c:38
(gdb) 
-- 
[田中 哲][たなか あきら][Tanaka Akira]