Software Exorcism: A Handbook for Debugging and Optimizing Legacy Code

Transcription

1 Software Exorcism: A Handbook for Debugging and Optimizing Legacy Code BILL BLUNDEN Apress

2 About the Author Acknowledgments Introduction xi xiii xv Chapter 1 Preventative Medicine Core Problems Time to Market Pressure Fluid Specifications Trade Features for Time Get It in Writing Complexity ' Defensive Programming Cohesion and Coupling Checking for Bad Input Data Scope Logging Documentation Design for Change Incremental Refinement Unit Testing Motivation Behind Automated Testing Steps Towards a Framework Framework Extensions Tool Configuration Use Compiler Warnings Build Settings Machine Dependencies Endianess Memory Alignment Data Type Sizes The Benefits of avirtual Machine Summary 67 The Bottom Line: Why Do Bugs Occur? 67 Refinement Checklist: Proactive Bug Prevention 68

3 Chapter 2 Debugging Tactics Initial Steps Duplicate the Bug Bugs That Can't Be Duplicated Verify the Bug Is Genuine Resolving the Bug: Quick Fixes Examine Recent Changes Use Tracing Information DejaVu A Know When to Quit Resolving the Bug: The Scientific Method General Approach Locating the Bug: Incremental Integration Locating the Bug: Binary Search A Understand the Problem Preventing Careless Errors Diagnostic Tools Basic Debugger Operation Record Keeping Individual Record Keeping Collaborative Record Keeping Summary 110 Chapter 3 Understand the Problem How Knowledge Is Lost Competition Attrition Promotion Poorly written Code Design Problems Obfuscation Misleading Code Reverse Engineering General Strategies Countermeasures Creating a Knowledge Base Summary 156 VI

4 Chapter 4 Debugger Internals Types of Debuggers Machine Debuggers vs. Symbolic Debuggers Debugging Infrastructures: Custom Built Debugging Infrastructures: System Calls Debugging Infrastructures: Interpreters Kernel Debuggers Interface: Command Line vs. GUI Symbolic Debugger Extensions Dynamic Breakpoints Single Stepping Countertactics System Calls Remove Debug Information Code Salting Mixed Memory Models Summary 211 Chapter 5 Optimization: Memory Footprint Forgotten History Program Layout in Memory Scenario: A Single Segment Scenario: Code and Data Segments Only Scenario: All Four Segment Types Code Segment Cut-and-Paste Programming Macros Dead Code Data Segment Dual-Use Data Structures Bit Fields Compression Algorithms Stack Segment Activation Records Function Parameters Local Variables 247 vu

5 5.6 Heap Memory Pools Recycling, Lazy Instantiation Tracking Memory Usage Summary 260 Chapter 6 Optimization: CPU Cycles Program Control Jumps Labels and GOTO Function Parameters Functions with a Varying Number of Arguments System Calls Recursion Program Control Branching Lookup Tables switch vs. if-else Common Case First, Infrequent Case Last Program Control Loops Loop Invariants Function Calls Array References Breaking Up Compound Boolean Expressions Loop Unrolling Loop Jamming Extracting Program Branching Statements Memory Management Dealing with the Overhead Locality of Reference Input/Output Caching Buffering Advanced Techniques Exceptions Dynamic Registration Model Static Table Model Dealing with Overhead Abusing Exceptions 308 vui

6 6.7 Expensive Operations Eliminate Common Subexpressions Floating Point Calculation Myths Strength Reduction A Synchronization Shorthand Operator Myths Quick Fixes Better Hardware Constrain the Problem Compiler Settings Summary Putting It All Together Chapter 7 Final Words of Advice Other Threats to Source Code Integrity 322 Fashionable Technology: A Case Study 323 Brainwashing The Real Issue Maintaining a Paper Trail 325 Quietly Keep Records 325 The Myth of Privacy History Repeats Itself 327 The "New Economy" Hits Home 328 Index 331 IX