I solved the problem. See [ruby-talk:17074]

# -----Original Message-----
# From: Yasushi Shoji [mailto:yashi / yashi.com] 
# Sent: 3 ???? 2001 ?. 23:51
# To: ruby-talk ML
# Subject: [ruby-talk:17192] Re: Building extension.
# 
# 
# At Fri, 29 Jun 2001 11:42:58 +0900,
# Aleksei Guzev wrote:
# > 
# > The problem was while I tried "rb_define_class" the interpreter 
# > aborted with segmentation fault.
# > 
# > That was the case while I used some "rb_c*" class as 
# Parent. As soon 
# > as I pass 0 instead of rb_cObject it works pretty well. 
# What's wrong?
# 
# It'd be easier if you post a fragment of your code.
# 
# btw, reading ext/dbm/dbm.c might help.
# 
# regards,
# --
#           yashi
#