BCI library for Java in C

I am looking for a BCI (Bytecode Instrumentation) library for Java in C or C++, to use in a JVMTI agent.

Best case scenario would be something like ASM or BCEL in pure C.

The closest thing I have found so far is only a demo java_crw_demo written by Kelly O'Hair a few years ago and used in Sun's/Oracle's tutorials ever since.

Do you know of anything else?

Some rationale: I am building an instrumentation tool to add a getter method to java.lang.Object and overload this getter in every direct subclass of Object. For this reason I cannot use a Java agent. Also, I would like to avoid spawning a secondary JVM to perform the instrumentation - for complexity and speed reasons.