ふなばです。

とりあえず、うちでは new の前に GC.start するとコアダンプさせることに
成功します。

class Foo < File
  def x
    @x = "x"
  end
end

GC.start

p Foo.new("foo.txt", "w").x

(gdb) w
#0  0x200f2801 in ?? ()
#1  0x200f2064 in ?? ()
#2  0x5ac0c in rb_bug (fmt=0x4661c "Segmentation fault") at error.c:154
#3  0x4663d in sigsegv (sig=11) at signal.c:377
#4  0xefbfdfdc in ?? ()
#5  0x526d9 in rb_ivar_set (obj=629452, id=8210, val=629352) at variable.c:865
#6  0x616f in rb_eval (self=629452, node=0x99a54) at eval.c:2337
#7  0x9549 in rb_call0 (klass=628572, recv=629452, id=8201, argc=0, argv=0x0, 
    body=0x999dc, nosuper=0) at eval.c:3897
#8  0x9884 in rb_call (klass=628572, recv=629452, mid=8201, argc=0, argv=0x0, 
    scope=0) at eval.c:3985
#9  0x5820 in rb_eval (self=675532, node=0x997e8) at eval.c:2183
#10 0x56ab in rb_eval (self=675532, node=0x997c0) at eval.c:2175
#11 0x44c2 in rb_eval (self=675532, node=0x99798) at eval.c:1720
#12 0x289c in eval_node (self=675532) at eval.c:967
#13 0x29f2 in ruby_run () at eval.c:994
#14 0x1611 in main (argc=2, argv=0xefbfd810, envp=0xefbfd81c) at main.c:39
(gdb) up 5
#5  0x526d9 in rb_ivar_set (obj=629452, id=8210, val=629352) at variable.c:865
865             st_insert(ROBJECT(obj)->iv_tbl, id, val);

/Just another Ruby hacker,/.source.display

ふなば ただよし