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