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
Source Code Repositories
• Collection of code changes
• Most long developed projects have one
• Typically used to store histories and make
backups
• Knowledge contained within hasn’t been
fully leveraged
– Previous development experience
– Changes that fix bugs are particularly
interesting
Horizontal Bug Finding Techniques
• Applicable across all projects
• Based on pre-defined bug patterns,
theorem proving, and model checking
• ESC/Java, FindBugs, JLint, PMD
Vertical Bug Finding Techniques
• Aim for project-specific bugs
• Different project requirements, business logic, and
semantics
• BugMem
– Learn bug patterns over time
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
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
Hunks
• Hunk pair (HP) → deleted hunk (DH) (bug
hunk (BH)) & added hunk (AH) (fix hunk
(FH))
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
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
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
Normalization Continued
• For a method call, actual parameters are
normalized to the type of the parameter
• Normalization level
– Indicates a component’s degree of
normalization amongst others extracted from
same raw component
– Level increases with degree of normalization
Examples
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
Diff Filtering
• Removes code unchanged between bug
and fix hunks
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
Options
Evaluation
Evaluation Continued
• Determine half and full hit rates
– Half hit – bug previously seen
– Full hit – bug and fix previously seen
• Five open source projects
Evaluation Continued
Evaluation Continued
Evaluation Continued
Comparison With PMD
Limitations
• Missing Memories
• Not applicable in initial stage of a project
• Doesn’t catch cross-file relationships
Uses
• Bug Finding Tool
– BugMem
– Can be integrated into Eclipse
• Code example repository
– Useful to developers new to a project
The End!
Questions?