if mm == nil {
			log.Fatalf("%s:%d: invalid errchk line: %s", file, lineNum, line)
		}
		for _, m := range mm {
			replacedOnce := false
			rx := lineRx.ReplaceAllStringFunc(m[1], func(m string) string {
				if replacedOnce {
					return m
				}
				replacedOnce = true
				n := lineNum
				if strings.HasPrefix(m, "LINE+") {
					delta, _ := strconv.Atoi(m[5:])
					n += delta