JxVm

• A mini incomplete VM for java byte code.
• Note: far from complete, maybe 90% of the simpler op codes are implemented.
• However can run a Hello World Application.
• Performance is slow, there is no linker yet and all lookups are done via Strings.
• No Exception (only throwing, but not catching)/Garbage Collection/Threading yet
• Needs a real java rutime library (e.g. OpenJDK) to start.
• Java methods can be overriden via C++-Methods
• Whole Java classes can be replaced (javalib). This is needed for stubbing out Thread-related startup code

Why?

• I Wanted to know internals of Java apps better.
• It made some fun.
  • Hello World takes 90000 Operations to run through.

Documentation used

• Nicer description of JVM Spec: http://cs.au.dk/~mis/dOvs/jvmspec/ref--35.html
• Class file format: https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.10.1.9.lconst_l
• Opcode list: https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-7.html

How to build/Run

Requirements

• Boost

• Only tested OSX 10.11 so far.

   # Java standard library is found via JAVA_HOME
   export JAVA_HOME=/* path to some java VM where it can find jre/lib/rt.jar */
   ./build_and_test.sh
  
   # Running Hello World.
   cd build/apps
   ./jxvm ../../manual_test/hello_world/HelloWorld.class
  

License

• MIT