Java Bytecode Level Debugging?

QuantumG asks: "I'm retargeting GCC (EGCS) to the Java Virtual Machine so that you can compile C to Java bytecode. I've been inserting System.out messages in my bytecode and hacking the output to get it past the verifier but I'm getting kinda annoyed at the fantastic error messages I get from the JVM (most the time it just bombs with an assert error). Does anyone know of a bytecode level debugger for Linux? The only one I've seen is a commercial package for the Mac."