Java 6 Decompiler

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• Java 6 Decompiler
• Joshua Cranmer

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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

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Last Time

• Class parsing
• 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

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Now

• Class parsing
• 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

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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 ltinitgt()V return becomes
• super() return

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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

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Future

• Cleanup of transformation sequences
• Start converting control structures
• Handle variables better