/** forward toString to handler */
mv = cw.visitMethod(ACC_PUBLIC, "toString", "()Ljava/lang/String;", null, null);
mv.visitCode();
mv.visitVarInsn(ALOAD, 0); // load self
mv.visitFieldInsn(GETFIELD, self_type, "handler", EFUNHANDLER_TYPE.getDescriptor());
mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Object", "toString", "()Ljava/lang/String;");
mv.visitInsn(ARETURN);
mv.visitMaxs(3, 3);
mv.visitEnd();
// make invoke_tail method