[Sablevm-developer] reflection classes for constant pool and bytecode data

[Andrew P. <apu...@ac...>]

Hi, SableVM developers!

I've been looking over the SableVM sources and I think the first step
toward creating a JIT should be the addition of a simple class hierarchy
containing native methods for exposing SableVM's internal representations
of the constant pool and (prepared) bytecodes to the Java environment.
I've been working this week with some classes I've cobbled together for
parsing class files directly from disk, but keeping the class data in
memory solely for a JIT's use is wasteful.

How does this look?

  public abstract class org.sablevm.vm.Constant 
  {
      public int size() { return 1; }
  };

  public class org.sablevm.vm.Constant_UTF8
      extends org.sablevm.vm.Constant 
  {
      public String value;
  };

  public class org.sablevm.vm.Constant_Unicode
      extends org.sablevm.vm.Constant
  {
      public char[] value;
  };

  public class org.sablevm.vm.Constant_Integer
      extends org.sablevm.vm.Constant
  {
      public int value;
  };

  public class org.sablevm.vm.Constant_Float
      extends org.sablevm.vm.Constant
  {
      public float value;
  };

  public class org.sablevm.vm.Constant_Long
      extends org.sablevm.vm.Constant
  {
      public long value;
      public int size() { return 2; }
  };

  public class org.sablevm.vm.Constant_Double
      extends org.sablevm.vm.Constant
  {
      public double value;
      public int size() { return 2; }
  };

  public class org.sablevm.vm.Constant_String
      extends org.sablevm.vm.Constant
  {
      public String value;
  };

  public class org.sablevm.vm.Constant_Class
      extends org.sablevm.vm.Constant
  {
      public int class_index;
  };

  public class org.sablevm.vm.Constant_Fieldref
      extends org.sablevm.vm.Constant
  {
      public int class_index;
      public int name_and_type_index;
  };

  public class org.sablevm.vm.Constant_Methodref
      extends org.sablevm.vm.Constant
  {
      public int class_index;
      public int name_and_type_index;
  };

  public class org.sablevm.vm.Constant_InterfaceMethodref
      extends org.sablevm.vm.Constant
  {
      public int class_index;
      public int name_and_type_index;
  };

  public class org.sablevm.vm.Constant_NameAndType
      extends org.sablevm.vm.Constant
  {
      public int name_index;
      public int signature_index;
  };

  public class org.sablevm.vm.Opcode  { ... };

  public class org.sablevm.vm.Code
  {
      public org.sablevm.vm.Class clazz;     // class containing this method
      public int access_flags;
      public int max_stack;
      public int max_locals;
      public int exception_table[][];
      public org.sablevm.vm.Opcode code[];   // method opcodes
      ...
  }

  public class org.sablevm.vm.Field
  {
      public int access_flags;
      public String name;
      public String signature;
      ...
  }

  public class org.sablevm.vm.Class
  {
      public org.sablevm.vm.Class superclass;     // superclass, if any
      public int access_flags;
      public org.sablevm.vm.Field fields[];       // class fields
      public org.sablevm.vm.Field methods[];      // class/interface methods

      // constructs a Class object from the internal representation of
      // class or interface 'name'
      public native org.sablevm.vm.Class (String name);

      // retrieve a Constant object for the constant located at index 'i'
      // for Class 'name'
      public static native org.sablevm.vm.Constant getConstant (String name,
                                                                int i);

      // returns a Code object encapsulating the given method's bytecodes,
      // exception table, max stack size, and max locals
      public static native org.sablevm.vm.Code getCode (String class,
                                                        String name,
                                                        String signature);

      // object method version of getConstant()
      public native org.sablevm.vm.Constant getConstant (int i);

      // object method version of getCode()
      public native org.sablevm.vm.Code getCode (String name, 
                                                 String signature);
  }

I've only jotted down read-only methods so far. Eventually there will need
to be an org.sablevm.vm.Class method for attaching prepared native code to
a given method.

Note that these are NOT clases I plan to keep JIT state in during
translation. There's an "org.sablevm.vm.jit.*" hierarchy I'm thinking over
at the moment.

I was thinking the native methods implementing these classes could be added
to libsablevm. The associated classes will need to be added to sablepath.
Seeing how both are pulled in only if they are part of the transitive
closure of referenced classes/functions/etc., they cost nothing if the "use
JIT" configure option is not enabled.


Andrew Purtell
from home -- apu...@ac...