unimplemented method を rb_funcall で呼び出すと [BUG] になるようです。

pathname で Pathname#lchmod を実装するのに File.lchmod を呼び出そうとして
  rb_funcall(rb_cFile, rb_intern("lchmod"), 2, mode, get_strpath(self))
としたら、File.lchmod が unimplemented method な GNU/Linux では、以下のように
  [BUG] vm_call0: unsupported method type (7)
となりました。

% ./ruby -rpathname -e 'Pathname("foo").lchmod(nil)'
-e:1: [BUG] vm_call0: unsupported method type (7)
ruby 1.9.3dev (2010-08-07 trunk 28891) [i686-linux]

-- control frame ----------
c:0004 p:---- s:0010 b:0010 l:000009 d:000009 CFUNC  :lchmod
c:0003 p:0018 s:0006 b:0006 l:000ff4 d:0021ec EVAL   -e:1
c:0002 p:---- s:0004 b:0004 l:000003 d:000003 FINISH
c:0001 p:0000 s:0002 b:0002 l:000ff4 d:000ff4 TOP
---------------------------
-- Ruby level backtrace information ----------------------------------------
-e:1:in `<main>'
-e:1:in `lchmod'

-- C level backtrace information -------------------------------------------
./ruby [0x8155332]
./ruby [0x818a7cf]
./ruby(rb_bug+0x36) [0x818a82a]
./ruby [0x814d630]
./ruby [0x814e404]
./ruby [0x814e357]
./ruby(rb_funcall+0xa2) [0x814e4ae]
/tmp/o0/lib/ruby/1.9.1/i686-linux/pathname.so [0xb77c68da]
./ruby [0x814a426]
./ruby [0x814a2c9]
./ruby [0x814989d]
./ruby [0x814548a]
./ruby [0x81526b6]
./ruby [0x8152e8f]
./ruby [0x805b262]
./ruby(ruby_exec_node+0x1c) [0x805b36b]
./ruby(ruby_run_node+0x3b) [0x805b33f]
./ruby [0x8059d88]
/lib/i686/cmov/libc.so.6(__libc_start_main+0xe5) [0xb75f0455]
./ruby [0x8059c81]

[NOTE]
You may have encountered a bug in the Ruby interpreter or extension libraries.
Bug reports are welcome.
For details: http://www.ruby-lang.org/bugreport.html

zsh: abort      ./ruby -rpathname -e 'Pathname("foo").lchmod(nil)'

なお、File.lchmod を Ruby から呼び出すのは問題なく可能です。

% ./ruby -e 'File.lchmod(nil, "foo")'
-e:1:in `lchmod': lchmod() function is unimplemented on this machine
(NotImplementedError)
        from -e:1:in `<main>'
-- 
[田中 哲][たなか あきら][Tanaka Akira]