return
	}

	if !strings.HasPrefix(val, "0x") {
		Exitf("-B argument must start with 0x: %s", val)
	}

	ov := val
	val = val[2:]

	const maxLen = 32
	if hex.DecodedLen(len(val)) > maxLen {
		Exitf("-B option too long (max %d digits): %s", maxLen, ov)
	}

	b, err := hex.DecodeString(val)
	if err != nil {
		if err == hex.ErrLength {
			Exitf("-B argument must have even number of digits: %s", ov)
		}