CALLER_BINDING_ISEQ 1114 vm_backtrace.c     rb_ary_store(frame, CALLER_BINDING_ISEQ, cfp->iseq ? (VALUE)cfp->iseq : Qnil);
CALLER_BINDING_ISEQ 1129 vm_backtrace.c     rb_ary_store(frame, CALLER_BINDING_ISEQ, Qnil); /* not available */
CALLER_BINDING_ISEQ 1234 vm_backtrace.c     VALUE iseq = rb_ary_entry(frame, CALLER_BINDING_ISEQ);