1. Java 6 Decompiler Joshua Cranmer

2. Steps of Decompilation
Parse Java class file
Recreate signatures
Convert bytecode to Java executable code
Verify bytecode
Perform trivial conversion
Reconstruct control structures
Scope & Type Variables
Simplify code

3. Last Time Class parsing: Signature recreation:
All required information recovered
Java 5 attributes recovered: signature, varargs, enums
Debug attributes recovered: variable names
Signature recreation:
Valid for any method, field, class
Enums, annotations partially destroyed
No inner classes

4. Now Class parsing: Signature recreation: Bytecode conversion:
Annotations fully recoverable
Signature recreation:
All information relating to annotations updated
Bytecode conversion:
Some simple types convertible
Some scoping and typing of variables
Minimal verification

5. Bytecode conversion Successive iterations of transforms
Many can be condensed at this point
Two main runs: StackAnalyzer + assorted
StackAnalyzer verifies bytecode, performs SSA analysis, asserts certain invariants
Assorted transforms provides trivial decompilation
Trivial:
aload_0; invokesuper <init>()V; return becomes
super(); return

6. Variable Scoping and Typing
MOST DIFFICULT PART
Creation of SSA form:
Each variable is only assigned to once
Maximal variable assumption
SSA unification: ongoing research
Type is easy iff variables are not over-scoped

7. Future Cleanup of transformation sequences
Start converting control structures
Handle variables better