Hawkbeans is a small (~6K LOC), MIT-licensed JVM written in C and intended for educational purposes. It does not meet the Java specification (not even close), but includes enough functionality for students to become familiar with concepts important to the JVM, viz. byte code interpretation, exceptions, class loading, resolution of symbolic references, exceptions, stack frames, and garbage collection.

Below are a list of features not supported in this JVM:

• Full exception support: only the basics.
• Reflection
• Floating point math is hardly tested
• User-defined class loaders
• Extremely limited JNI
• No JIT compilation
• Wide word support is limited
• No actual protection is implemented (i.e. private/public etc.)

Hawkbeans uses a simple buddy allocator with power of 2 free lists for heap management. This code was taken from several other OS code bases.

Hawkbeans was developed referencing Oracle's Java Virtual Machine Specification.

You'll need a JDK 1.8 environment installed to build programs to run with Hawkbeans (i.e. using javac).

To build the JVM, simply run make. To build the Java libs (required for building test programs) run make jlibs.

Hawkbeans can be run as follows:

$> ./hawkbeans SomeClass.class

Note the difference with invoking the normal JVM. Here we explicitly provide the .class suffix. This may change.

The source is organized into the following directories:

• src: The code for the platform-independent portion of Hawkbeans. Note this organization is not very sane at the moment.
  • arch/x64-linux: The linux specific code. Soon there will be a hawknest directory.
• include: The header files for the code.
• javasrc: The Java code for the Hawkbeans standard libraries.
• scripts: Various utility scripts, mostly used when I wrote the code.
• testcode: A set of simple Java programs to test functionality

Contact Kyle C. Hale [email protected] for questions/comments.