1. Debugging Memory Issues
William Cohen
NCSU CSC 591W
February 20, 2008

2. Memory Problems: Uninitialized memory Memory leaks Double frees
Out of bound array accesses
Null pointers
Memory corruption
FOSS Tools/Solutions:
Valgrind
Mudflap

3. Valgrind Introduction
Provides a number of tools to analyze programs:
Memory error checkers
Heap profiler (catch excessive memory use)
Cache profiler (also give coverage information)
Works code using shared libraries and threads
Available for i386 and x86_64 Linux

4. Valgrind Concepts Instruments executables with binary rewrites
Works with existing executables and shared libs
Avoids recompiling code
Tools instrument particular operations and functions (e.g. Memory reads/writes and malloc)
Space and time overheads introduced by instrumentation and binary rewrites
Can write custom instrumentation

5. Valgrind Memory Error Detection (memcheck)
Tracks memory allocated and freed
Detects reads/writes to uninitialized and freed memory
Detects memory leaks

6. Valgrind Heap Profiler (massif)
Provides information on:
Number of heap blocks
Amount of memory used
Stack sizes
Tool output includes summaries for each process.

7. Valgrind Cache Profiler (cachegrind)
Simulates processors caches
Can provide code coverage information

8. Valgrind Demonstrations

9. Mudflap Introduction Compile-time instrumentation
Shared libraries are not instrumented
Includes array bounds checking
Built into recent versions of gcc

10. Mudflap Demonstrations

11. Further Reading
Steve Best, Linux Debugging and Performance Tuning: Tips and Techniques, Prentice Hall, 2006.