DDT and Totalview. HRSK Practical on Debugging,

Transcription

1 Center for Information Services and High Performance Computing (ZIH) DDT and Totalview HRSK Practical on Debugging, Zellescher Weg 12 Willers-Bau A106 Tel Matthias Lieber (matthias.lieber@tu-dresden.de) Tobias Hilbrich (tobias.hilbrich@zih.tu-dresden.de)

2 Content DDT vs. Totalview Running a program under DDT Running a program under Totalview Demo Exercises DDT and Totalview 2

3 Allinea Distributed Debugging Tool (DDT) Process control: run, stop, stepping Process and thread selection Source file browser Source view Variables pane Output, Breakpoints, Watchpoint, Call stack Evaluation window DDT and Totalview 3

4 Totalview Process control: run, stop, stepping Variables Call stack Source view Variable evaluation window Breakpoints, watchpoints DDT and Totalview 4

5 DDT vs. Totalview DDT Totalview Graphical user interface C, C++, Fortran Array data visualization Memory debugging Parallel applications: pthreads, OpenMP, MPI, hybrid Internally uses GDB Own backend Licenses at HRSK 32 Licenses at HRSK DDT and Totalview 5

6 Example: Debugging with DDT on Mars Compiling myproc.c Starting DDT to debug myprog Loading module for DDT Starting interactive batch session DDT and Totalview 6

7 Example: Debugging with DDT on Mars Run and Debug a Program DDT and Totalview 7

8 Example: Debugging with DDT on Mars Run DDT and Totalview 8

9 Example: Debugging with DDT on Mars Hit Play Button to start program DDT and Totalview 9

10 Example: Debugging with DDT on Mars Segmentation Fault! Hit Pause to stop the program DDT and Totalview 10

11 Example: Debugging with DDT on Mars This is the line where the program crashed DDT and Totalview 11

12 Viewing Array Data in C: DDT Array Expression: mygrid.theta[$i][$j] DDT and Totalview 12

13 Example: Debugging with Totalview on Mars Compiling examplef Loading module for Totalview Starting Totalview to debug examplef DDT and Totalview 13

14 Example: Debugging with Totalview on Mars Hit Go to run the program DDT and Totalview 14

15 Example: Debugging with Totalview on Mars Select different stack frame to locate position in code Program stopped due to segmentation violation DDT and Totalview 15

16 Example: Debugging with Totalview on Mars This is the line where the program crashed DDT and Totalview 16

17 Example: Debugging with Totalview on Mars Diving Double click on grid opens the variable window Double click on theta shows content of the array theta DDT and Totalview 17

18 Example: Debugging with Totalview on Mars Content of the array theta DDT and Totalview 18

19 Viewing Array Data in C: Totalview Expression: **(mygrid.theta) Type: double[22][22] DDT and Totalview 19

20 Conditional Breakpoints in DDT and Totalview DDT Add a breakpoint (right-click on a source code line or double click on line number) Open the Breakpoints tab Enter condition in the condition column, e.g. step==100 Totalview Add a breakpoint (right-click on a source code line or double click on line number) Open the Action Points tab Right-click on the added breakpoint -> Properties... Select Evaluate Enter condition, e.g. if(step==100) $stop Note: Other format as in GDB or DDT! DDT and Totalview 20

21 Demo with DDT and Totalview firstc Start program Stepping Program crash Core dump examplec Breakpoints Call stack Conditional breakpoints Examine Variables Examine Arrays Array Visualization examplef-05 Attach to running program DDT and Totalview 21

22 Exercise 1: Learn to work with DDT & Totalview DDT: module load ddt ddt <executable> Totalview: module load totalview totalview <executable> Play around with firstc / firstf Play around with examplec / examplef Use a conditional breakpoint to find out the value of dthetamax after step 100 has been computed Find out in which iteration step the grid value at theta(15,10) becomes larger than 0 DDT and Totalview 22

23 Exercise 2: Find the Bug! Program crashes: examplec-01.c or examplef-01.f90 examplec-02.c or examplef-02.f90 Fortran programmers: also try ifort option C Warning: Do not run Fortran version without debugger! Logical mistakes: examplec-04.c or examplef-04.f90 examplec-05.c or examplef-05.f90 Hint: observe what happens to the theta array Use DDT or/and Totalview If you still have some time: try to find the bugs with GDB DDT and Totalview 23

24 Exercise 2: Solution examplec-01.c or examplef-01.f90 thetanew is not allocated How to find: examine thetanew Fortran: unknown bounds, unassociated C: expression cannot be evaluated, 0x0 examplec-02.c or examplef-02.f90 theta and thetanew array bounds too small How to find: Fortran: breakpoint, compare array bounds with loop indices C: look at theta[20][0] DDT and Totalview 24

25 Exercise 2: Solution examplec-04.c or examplef-04.f90 Error in heatboundary, boundaries are not set properly How to find: Examine the theta array while stepping through the time steps Boundaries will always be zero examplec-05.c or examplef-05.f90 Forgot to copy thetanew to theta in heattimestep How to find: Look at iteration step count: much higher than in correct version Examine theta: data does not change when stepping through the iteration steps DDT and Totalview 25