1ftrace.sno:16 stmt 16: level 0 call of A(), time = xxx
2ftrace.sno:10 stmt 10: level 1 call of B(), time = xxx
3ftrace.sno:11 stmt 11: level 2 call of C(), time = xxx
4ftrace.sno:12 stmt 12: level 3 call of D(), time = xxx
5ftrace.sno:14 stmt 14: level 3 RETURN of D = '', time = xxx
6ftrace.sno:13 stmt 13: level 3 call of D(), time = xxx
7ftrace.sno:14 stmt 14: level 3 RETURN of D = '', time = xxx
8ftrace.sno:13 stmt 13: level 2 RETURN of C = '', time = xxx
9ftrace.sno:11 stmt 11: level 1 RETURN of B = '', time = xxx
10ftrace.sno:10 stmt 10: level 0 RETURN of A = '', time = xxx
11