RUBY_VM_NEXT_CONTROL_FRAME  447 vm_backtrace.c       RUBY_VM_NEXT_CONTROL_FRAME(
RUBY_VM_NEXT_CONTROL_FRAME  448 vm_backtrace.c 	  RUBY_VM_NEXT_CONTROL_FRAME(start_cfp)); /* skip top frames */
RUBY_VM_NEXT_CONTROL_FRAME  460 vm_backtrace.c     for (i=0, cfp = start_cfp; i<size; i++, cfp = RUBY_VM_NEXT_CONTROL_FRAME(cfp)) {