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Bug Isolation via Remote Program Sampling

Bug Isolation via Remote Program Sampling. Ben Liblit, Alex Aiken Alice X. Zheng, Michael I. Jordan UC Berkeley . Presented by Chao Liu. Debugging is Hard. Limited Resource Time Human Efforts Test Cases Triage and Guesswork.

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Bug Isolation via Remote Program Sampling

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  1. Bug Isolation viaRemote Program Sampling Ben Liblit, Alex Aiken Alice X. Zheng, Michael I. Jordan UC Berkeley Presented by Chao Liu

  2. Debugging is Hard • Limited Resource • Time • Human Efforts • Test Cases • Triage and Guesswork • Windows 2000, 35M LOC, 63,000 known bugs at the time of release, 2 per 1000 lines • --Quoted from Monica Lam’s Slides

  3.  € ƒ ‚ ƒ €  Leverage End-users Predicates ShippingApplication ProgramSource Sampler Compiler StatisticalDebugging Counts& J/L Top bugs withlikely causes Courtesy of Ben Liblit

  4. Outline • Low-overhead Sampling • Bug Isolation • Related Works • Conclusion and Discussion

  5. Low-overhead Sampling • Program predicate • Any proposition • Fingerprint of execution • Straightforward Checking

  6. Periodical Countdown counter = 100 while ( … ){ if(--counter == 0){ check(p != Null); counter = 100; } p = p->next; if(--counter == 0){ check(i < max) ; counter = 100; } total += size[i]; }

  7. Randomize it! • No free lunch

  8. From Bernoulli to Geometric • Randomized • Fair • Low-overhead

  9. Outline • Low-overhead Sampling • Bug Isolation • Related Works • Conclusion and Discussion

  10. Bug Isolation • Assumptions • Predicates capture incorrect behavior. • Each predicate P should always be false during correct execution. • Therefore, when P is true, the program • either fails (a deterministic bug) • or is at increased risk of failing (a nondeterministic bug).

  11. Isolating Deterministic Bug • Winnowing Strategy • Predicates observed true on some bad runs • Predicates never observed true on any good run • Case Study: ccrypt • Instrument scalar return sites, 570 • 3 × 570 = 1710 counters • Simulate large user community • 2990 randomized runs; 88 crashes

  12. Winnowing • 1710 counters • 1569 are always zero • 141 remain • 139 are nonzero on some successful run • Not much left! file_exists() > 0 xreadline() == 0 Courtesy of Ben Liblit

  13. Non-deterministic Bug • Logistic Regression

  14. Maximum Likelihood Estimation Maximize the log-likelihood function where

  15. Regularized Logistic Regression Maximize the penalized log-likelihood function where

  16. Case Study: bc-1.06 void more_arrays () { old_count = a_count; a_count += STORE_INCR; /* Copy the old arrays. */ for (indx = 1; indx < old_count; indx++) arrays[indx] = old_ary[indx]; /* Initialize the new elements. */ for (; indx < v_count; indx++) arrays[indx] = NULL; … } #1: indx > scale #1: indx > scale #2: indx > use_math #1: indx > scale #2: indx > use_math #3: indx > opterr #4: indx > next_func #5: indx > i_base Courtesy of Ben Liblit

  17. Bug Found: Buffer Overrun void more_arrays () { old_count = a_count; a_count += STORE_INCR; /* Copy the old arrays. */ for (indx = 1; indx < old_count; indx++) arrays[indx] = old_ary[indx]; /* Initialize the new elements. */ for (; indx < v_count; indx++) arrays[indx] = NULL; … } Courtesy of Ben Liblit

  18. Outline • Low-overhead Sampling • Bug Isolation • Related Works • Conclusion and Discussion

  19. Related Work • Fault Localization • Program spectra-based • NN/Perm [RR03], ASE’03 • Memory graph-based • Delta-Debugging [Z02], FSE’02 • Cause-Transition (CT) [CZ05], ICSE’05 • Predicate-based • Liblit03 [LA+03], PLDI’03 • Liblit05 [LN+05], PLDI’05 • SOBER [LY+05], FSE’05 • …

  20. Quality Comparison • CT vs. NN/Perm [CZ05]

  21. Shameless Advertisement [LX+05]

  22. Outline • Low-overhead Sampling • Bug Isolation • Related Works • Conclusion and Discussion

  23. Conclusions • Fault localization is possible • Semantic bugs can be also localized • Intense competition in this problem

  24. Discussion • How many of you believe in the applicability of fault localization • Industry use, … • Personal use, … • Is low, say less than 10%, overhead acceptable to you?

  25. References • [RR03] M. Renieris and S. Reiss. Fault Localization with nearest neighbor queries. In Proc. 18th IEEE Int. Conf. Automated Software Engineering (ASE’03), 2003. • [CZ05] H. Cleve and A. Zeller. Locating causes of program failures. In Proc. 27th Int. Conf. Software Engineering (ICSE’05), 2005. • [LN+05] B. Liblit, M. Naik, A. Zheng, A. Aiken, and M. Jordan. Scalable statistical bug isolation. In Proc. ACM SIGPLAN 2005 Int. Conf. Programming Language Design and Implementation (PLDI’05), 2005. • [LA+03] B. Liblit, A. Aiken, A. Zheng, and M. Jordan. Bug isolation via remote program sampling. In Proc. ACM SIGPLAN 2003 Int. Conf. Programming Language Design and Implementation (PLDI’03), pp. 141–154, 2003. • [Z02] A. Zeller. Isolating cause-effect chains from computer programs. In Proc. ACM 10th Int. Symp. Foundations of Software Engineering (FSE’02), 2002. • [LY+05] C. Liu, X. Yan, L. Fei, J. Han and S. Midkiff, SOBER: Statistical Model-based bug Localization. In Proc. ACM 13th Int. Symp. Foundations of Software Engineering (FSE’05), 2005.

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