Memories of Bug Fixes

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Memories of Bug Fixes

• Sunghun Kim, Kai Pan, and E. James Whitehead Jr.,
  University of California, Santa Cruz
• Presented By Gleneesha Johnson
• CMSC 838P, Fall 2006

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Source Code Repositories

• Collection of code changes
• Most long developed projects have one
• Typically used to store histories and make
  backups
• Knowledge contained within hasnt been fully
  leveraged
• Previous development experience
• Changes that fix bugs are particularly interesting

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Horizontal Bug Finding Techniques

• Applicable across all projects
• Based on pre-defined bug patterns, theorem
  proving, and model checking
• ESC/Java, FindBugs, JLint, PMD

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Vertical Bug Finding Techniques

• Aim for project-specific bugs
• Different project requirements, business logic,
  and semantics
• BugMem
• Learn bug patterns over time

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Bug Fix Memories

• Project-specific bug and fix knowledge base
• Developed by analyzing history of bug fixes
• Can be used to detect bugs and suggests fixes

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Building Bug Fix Memories

• Extract source code, change logs, and deltas
• Kenyon
• File change
• Contains list of region pairs that show
  differences between two file versions.
• Regions called hunks
• Consist of source code lines
• Identify changes where a bug was fixed
• Keyword search
• Search for references to bug reports

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Hunks

• Hunk pair (HP) ? deleted hunk (DH) (bug hunk
  (BH)) added hunk (AH) (fix hunk (FH))

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Extracting Components From Hunks

• Extracts syntax patterns, components, from hunks
• Parsing extracts syntax components
• Normalizing generalizes syntax to match similar
  code
• Filtering eliminates noise
• Information filtering
• Diff filtering

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Raw Component Extraction (Parsing)

• Preprocessing
• Basic syntax lines
• Differentiate between composite statements (if,
  for, while) and simple statements (method call,
  assignment, etc.)
• all multi-line simple statements are on a single
  line.
• conditional predicates of if, for, while, etc.
  all lie on a single line.
• Raw components
• Based on abstract syntax tree of basic syntax
  line
• 4 kinds static Java call, Java call,
  user-defined call, and non-call

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Normalization

• If the variable type of a raw component is known,
  normalize variable
• i.e., foo.flag ? Foo.flag
• Generate two components for raw components that
  contain numeric, boolean, char or string literals
• One with and one without normalization for the
  literal
• i.e., i 1 ? int 1 int int

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Normalization Continued

• For a method call, actual parameters are
  normalized to the type of the parameter
• Normalization level
• Indicates a components degree of normalization
  amongst others extracted from same raw component
• Level increases with degree of normalization

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Examples
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Information Filtering

• Information value indicates how much unique
  information a component carries
• Determined by summing information value of its
  elements
• Information value threshold used to filter
  components with little unique information
• Two is used as a threshold in the paper

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Diff Filtering

• Removes code unchanged between bug and fix hunks

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Searching Memories

• Bugs found by searching for matching patterns in
  bug hunks
• Suggestions made by returning code in
  corresponding fix hunks
• Several options for component searching
• Adjust degree of matching and omission of very
  common components

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Options
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Evaluation
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Evaluation Continued

• Determine half and full hit rates
• Half hit bug previously seen
• Full hit bug and fix previously seen
• Five open source projects

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Evaluation Continued
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Evaluation Continued
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Evaluation Continued
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Comparison With PMD
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Limitations

• Missing Memories
• Not applicable in initial stage of a project
• Doesnt catch cross-file relationships

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Uses

• Bug Finding Tool
• BugMem
• Can be integrated into Eclipse
• Code example repository
• Useful to developers new to a project

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The End!
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Questions?