unwind_user_frame
tail = unwind_user_frame(tail, cookie, consume_entry);
fp = unwind_user_frame(consume_entry, cookie, fp, regs->ra);
fp = unwind_user_frame(consume_entry, cookie, fp, 0);
const struct unwind_user_frame *frame)
const struct unwind_user_frame fp_entry_frame = {
const struct unwind_user_frame fp_frame = {