/Scarlet

A work in progress Scala decompiler

Primary LanguageScalaMIT LicenseMIT

Scarlet

A work in progress Scala decompiler and reverse engineering tool/library. There isn't much interesting stuff happening here yet. Come back later and maybe I've gotten further with this.

Usage

java -jar scarlet.jar <input-file> [language]

The language specifies how far to parse and process the classfiles. Most will likely not be useful.

The more common ones that you will probably normally use are:

  • scala-2.11: TODO
  • scala-2.12: TODO
  • scala-2.13: TODO
  • scala-3: TODO
  • java: TODO

The complete list is.

  • raw-classfile: Reads the classfile without resolving any references in the constant pool or any other further processing.
  • classfile: Reads the classfile, resolves some references, but nothing more.
  • raw-bytecode: Parses the bytecode of the methods, but does not resolve references to the constant pool, or do any other processing.
  • bytecode: Reads the bytecode of the methods, resolves references to the constant pool, and removes specialization.
  • sir: Scarlet's first IR. A stackless IR, close to but not exactly the same as bytecode. Based on the IR from this paper
  • sir-syntax: Same as sir, but prints it in a more readable format, looking more like normal code.
  • sir-classsyntax: Same syntax as sir-syntax but also transforms the class around the methods to Scala code.
  • sir-cfg: GraphViz format with SIR organized by control flow graph.
  • sir-cfg-syntax: GraphViz format file with SIR syntax organized by control flow graph.
  • sir-cfg-classsyntax: Same syntax as sir-cfg-syntax but also transforms the class around the methods to Scala code.

Stuff that still needs to be done

  • Parse classfiles
  • Parse OPCode
  • Remove the stack
  • Construct CFGs
  • Structuring
  • Try-Catch stuff
  • Lambdas
  • Rewrite statements to expressions where it makes sense
  • Rewrite match expressions ending with MatchError
  • Rewrite match expressions not ending with MatchError
  • Recover lost generics types using type inference
  • Recover top level lazy vals
  • Recover method level lazy vals
  • Inline most values produced by the decompilation process
  • Remove most unit values
  • Recover traits original form where they can hold arbitrary code
  • Group seperate classes that belong together in one file

Goals

The end goal for Scarlet is to be able to decompile Java and Scala code and return a high level representation of the bytecode. This includes recovering information not present in the bytecode like generics and more advanced types like existentials, dependant and higher kinded types.

It should be able to do this both with and without the information provided by extra attributes found in the classfile.

Where does the name come from?

Nowhere really, but if you really want an explanation, let's go with SCAla Reverse Language Engineering Tool.

References

https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-2.html
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html
https://www.ndss-symposium.org/ndss2015/ndss-2015-programme/no-more-gotos-decompilation-using-pattern-independent-control-flow-structuring-and-semantics/
https://www.backerstreet.com/decompiler/frameless_functions.php
https://www.researchgate.net/publication/2645337_Analyzing_Control_Flow_in_Java_Bytecode
http://people.irisa.fr/David.Pichardie/papers/aplas10.pdf https://eli.thegreenplace.net/2015/directed-graph-traversal-orderings-and-applications-to-data-flow-analysis/