Minimal Instrumentation for Software Feature Location

1. Minimal Instrumentation for Software Feature Location Sharon Simmons Dennis Edwards Norman Wilde Eric Daniels

2. Software Reconnaissance Where in this program is feature X implemented? 100’s KLOC, 10’s MLOC Modification required Interactions forgotten • Solution: track execution Feature is active 1. Run tests without the feature 2. Run tests with the feature Feature is NOT active • 3. Compare what was executed Components executed in the first group of tests, but not in the second group Marker Components Begin exploration here! ~Set difference UWF - Simmons

3. TraceGraph 4 Row Instrumentation point Column test case Col 1 without feature Col 2+ with feature Identifies “markers” Gives big picture Subroutine (En… 0 be_aas_bspq3.c /research/ope… 147 (demo of version 3) http://www.cs.uwf.edu/~recon/recon3/r3wDemo.htm UWF - Simmons

4. Software Recon Status • Developed for several years at UWF • Stable, usable, and free • Published works enumerate benefits and limitations • Brief Benefits • Identifies a small number of marker components • Identifies good places to start efficient code exploration • Can decrease software maintenance time UWF - Simmons

5. Instrumentation Alternatives Atom (Digital Equipment Corp) • Instrumentation at load time Pin (Intel Corp) • Instrumentation at dynamic link time CodeTEST (Freescale Semiconductor) • Instrumentation of preprocessed source code Recon (UWF) • Instrumentation of source code Gcov (GNU) • Instrumentation by (GNU) compiler None completely successful UWF - Simmons

6. Problems Encountered Newer systems time-sensitive Deadlines must be met Tracing can not be intrusive Target must execute normally Hard / soft real-time Race conditions Timing faults Initialization was hours instead of minutes Deadlines were not met Tracing intrusive and prevented normal execution UWF - Simmons

7. Our Approach • Instrument preprocessed source • Efficient code coverage tracing • Build IDB prior to execution • Provide facilities to partition execution into intervals • Simplify installation and use UWF - Simmons

8. Information Flow Source During Compilation During Execution IDB After Execution Instrumenter Trace Records Target Data Joiner Test Cases Driver Interval Delimiter Collection Engine Bitstring Traces UWF - Simmons

9. MinInst Overview Instrumentation point represented as bit • 1MB RAM ≈ 8.4M instrumentation points Ordered set of bits (bit string) represents code • Bit index identifies IDB record • Bit string cleared at interval start • Bit set when instrumentation point executed 0  not executed; 1  executed • Execution order not retained • Execution frequency not retained • Bit string saved at interval end UWF - Simmons

10. MinInst Details Two bitstrings allocated in shared memory • Active (A): currently accessed by target • Passive (P): prepared for next interval Collection Engine • Started as first instruction in main() • Wait for signal (no overhead here) • Exchange A & P bitstrings (pointer swap) • Save P bitstring to trace file (I/O overhead) • Clear P bitstring for next interval • Go back to step 1 UWF - Simmons

11. Version A • Instruments C/C++ • Linux platform • CodeTEST • Identifies instrumentation points • Builds IDB • MinInst • Inserts instrumentation code • Builds bit index  IDB map • Driver • Delimits trace intervals • Performs test cases • Collection Engine • Records bitstring trace at runtime • Joiner • Combines IDB, MAP and bitstring trace • Creates usable trace file UWF - Simmons

12. Information Flow Source During Compilation During Execution IDB After Execution Instrumenter CodeTEST Map MinInst Trace Records Target Data Joiner Test Cases Driver Interval Delimiter Collection Engine Bitstring Traces UWF - Simmons

13. Test Cases Generated Code • 1 file, simple functions (5 stmts, 5 inst pts) • 15KLOC, 30KLOC, 45KLOC, 60KLOC • CodeTEST: +200% MinInst: +11% Apache web server (httpd) • 550 files, 300KLOC, multithreaded, multiprocess • CodeTEST: +717% MinInst: +1% Openarena & OpenGL • 1K files, 700KLOC, time sensitive, multiplayer, networked • CodeTEST: +9371% MinInst: +6% UWF - Simmons

14. Shortcomings • Complexity of use • Reliance on CodeTEST • CodeTEST failed some test cases • Execution differences between platforms • Licensed software • Unsupported for a while UWF - Simmons

15. Version B • Prototype written in C for C/C++ source • Removed CodeTEST dependency • Tested in Linux • Windows port is pending • Simplified installation and use • Installation/removal scripts • Integrated into GCC/Make in Linux • Integrated into Visual Studio IDE • Interval options • Timed or user controlled UWF - Simmons

16. Information Flow Source During Compilation During Execution IDB After Execution Instrumenter MinInst Trace Records Target Data Joiner Test Cases Driver Interval Delimiter Collection Engine Bitstring Traces UWF - Simmons

17. Summary Version B status • Execution time unaltered from Version A • Linux and Windows XP • GCC and Visual Studio • Test cases in progress Next steps • Conclude test cases • Northrop Grumman large system testing • Complete distribution package Future Work • Modify TraceGraph for bit string operation UWF - Simmons

18. Information Flow Source During Compilation During Execution IDB After Execution MinInst Target Test Cases Driver Interval Delimiter Collection Engine Bitstring Traces UWF - Simmons

19. Contact Information Sharon Simmons ssimmons2@uwf.edu Dennis Edwards dedwards@uwf.edu Norman Wilde nwilde@uwf.edu UWF - Simmons