こんばんは、sheepman です。
次のようにすると core を吐きます。

$ cat t.rb
fork do
  break
end

$ ./miniruby -v t.rb
ruby 1.9.0 (2005-11-18) [i686-linux]
YARVCore 0.3.3 (rev: 358) [opts: ]
DBG> : "t.rb:1:in `<main>'"
-- stack frame ------------
0x402b1008 (0000): 00000001
0x402b100c (0001): 00000004
0x402b1010 (0002): 40298068
0x402b1014 (0003): 402af204
0x402b1018 (0004): 40330fa5 <- lfp <- dfp
-- control frame ----------
c:0004 p:-001 s:0005 b:0005 l:0004 d:0004 CFUNC  i:fork     s:         -
c:0003 p:0007 s:0003 b:0003 l:-173 d:-173 TOP    i:<main>   s:
c:0002 p:-001 s:0001 b:0001 l:0000 d:0000 FINISH i:-        s:         -
c:0001 p:-001 s:0000 b:-001 l:0000 d:0000 ------ i:-        s:         -
---------------------------
[BUG] Segmentation fault
ruby 1.9.0 (2005-11-18) [i686-linux]

以下はバックトレースです。

(gdb) bt
#0  0x400ecc11 in kill () from /lib/i686/libc.so.6
#1  0x4002a341 in pthread_kill () from /lib/i686/libpthread.so.0
#2  0x4002a6bb in raise () from /lib/i686/libpthread.so.0
#3  0x400ec8a4 in raise () from /lib/i686/libc.so.6
#4  0x400ee008 in abort () from /lib/i686/libc.so.6
#5  0x080c903e in rb_bug (fmt=0x80f2271 "Segmentation fault") at ../yarv/error.c:173
#6  0x080a12f3 in sigsegv (sig=11) at ../yarv/signal.c:457
#7  0x4002ce8e in __pthread_clock_settime () from /lib/i686/libpthread.so.0
#8  0x400ec908 in killpg () from /lib/i686/libc.so.6
#9  0x08058662 in ruby_cleanup (ex=2) at ../yarv/eval.c:246
#10 0x080587b2 in ruby_stop (ex=2) at ../yarv/eval.c:288
#11 0x08086b0e in rb_f_fork (obj=1076556292) at ../yarv/process.c:1424
#12 0x080b8d5f in call_cfunc (func=0x8086aa8 <rb_f_fork>, recv=1076556292, len=1073937284,
    argc=0, argv=0x6) at call_cfunc.h:21
#13 0x080b6e97 in th_eval (th=0x813d1d8, initial=0) at insns.def:1338
#14 0x080b89d1 in th_eval_body (th=0x813d1d8) at ../yarv/vm.c:1274
#15 0x080b9cfc in yarvcore_eval_iseq (iseq=1076462012) at yarv.h:49
#16 0x0805876c in ruby_exec_internal () at ../yarv/eval.c:269
#17 0x080587a0 in ruby_exec () at ../yarv/eval.c:281
#18 0x080587db in ruby_run () at ../yarv/eval.c:298
#19 0x08055ee1 in main () at ../yarv/main.c:36
#20 0x400d9c1f in __libc_start_main () from /lib/i686/libc.so.6

-- 
sheepman / TAMURA Takashi
sheepman sheepman.sakura.ne.jp http://sheepman.parfait.ne.jp/

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