def ret_start_point(pn: str, keyword: bytes):
    """
    1) return cid and tid from this example line
    CALLID[3] TID[3756] IJ T2M 0x63621040->0x65cf6450(avformat-gp-57.dll!avformat_open_input+0x0)
    2) for now, this function is case sensitive
    """
    with open(pn, 'rb') as f:
        lines = f.readlines()
        for line in lines:
            if keyword in line and b"0x0" in line:
                cid = int(line.split(b"CALLID[")[1].split(b"]")[0])
                tid = int(line.split(b"TID[")[1].split(b"]")[0])
                return cid, tid

        raise Exception("Cannot find the starting function from the trace file")