Injecting code into JVM classes using Byteman 1.0.3 and Java 5 JVM

[pontus.ullgren]

Hello,

I try to inject code into JVM classes and unfortuantly I need to do this on a system running Java 5 JVM, so I'm stuck using byteman 1.0.3.

However using byteman 1.0.3 I fail to get the result I expect.

As a POC we can use the example from the Byteman Tutorial

https://community.jboss.org/wiki/ABytemanTutorial#how_do_i_inject_code_into_jvm_classes

Executing this with latest byteman works as expected, however when I change to byteman 1.0.3 it does not work anymore.

If this a known limitation or is there a way to solve this and get code injected into JVM classes ?

{code}
ponu@devws:~/work$ export BYTEMAN_HOME=/opt/byteman-download-2.0.4
ponu@devws:~/work$ java -Dorg.jboss.byteman.debug=true -Dorg.jboss.byteman.transform.all -javaagent:${BYTEMAN_HOME}/lib/byteman.jar=script:./thread.btm,boot:${BYTEMAN_HOME}/lib/byteman.jar -cp . AppMain2 test
Default helper activated
Installed rule using default helper : trace thread start
*** start for thread: test
test
ponu@devws:~/work$ export BYTEMAN_HOME=/opt/byteman-1.0.3
ponu@devws:~/work$ java -Dorg.jboss.byteman.debug=true -Dorg.jboss.byteman.transform.all -javaagent:${BYTEMAN_HOME}/lib/byteman.jar=script:./thread.btm,boot:${BYTEMAN_HOME}/lib/byteman.jar -cp . AppMain2 test
test
ponu@devws:~/work$ 
{code}

Best regards

Pontus Ullgren

[adinn]

Hi Pontus,

Pontus Ullgren wrote:

Executing this with latest byteman works as expected, however when I change to byteman 1.0.3 it does not work anymore.

If this a known limitation or is there a way to solve this and get code injected into JVM classes ?

Yes, this is a known limitation of JDK5. The problem is that in JDK5 an agent transformer can only modify classes as they are loaded. Unfortunately java.lang.Thread is already loaded into the system before the Byteman agent is loaded so it never gets a chance to change this class. That's not the case for all classes in teh bootstrap classpath but it is fo rmany of the interesting ones. You can transform bootstrap classes  if they are i) not loaded before the Byteman agent andf ii) not needed by the agent in order to perform the transformation. Otherwise you eill need to use JDK6 and Byteman versions >= 1.2.x.

[pontus.ullgren]

I was afraid that I would get this answer :-)

I will see if we can switch to JDK6 for the testing of this or if there is some other way I can rewrite the rule so that it only needs to change classes that are not loaded before the byteman agent.

Thanks

Pontus Ullgren