Native Image support for Java Agent

[yswdqz]

Hi 👋
I am currently undertaking research on native-image support for Java Agents. However, I have encountered numerous challenges and feel uncertain about how to proceed.

I've read #1065, and other issues about javaagent. It appears that javaagent is not officially supported. Does this mean that I can go about getting native-image to support javaagent in my own way?

Thank you for considering my request. Any help is really appreciated !

[christianwimmer]

We are working on basic support for JVMTI agents (so agents written in C). We can support some of the JVMTI capabilities there, but certainly not any kind of bytecode transformation.

But I assume with "Java Agents" you mean the Java instrumentation API. This API does not really support much more than bytecode transformation, and since that cannot be done at image run time, there is not much point in loading such agents at run time.

All bytecode transformation must be done at image build time.

[yswdqz]

Thank you for your help !
I also found that Java on Truffle can run in the context of a native executable while still allowing dynamically-loaded bytecodes. Can I use it to support bytecode transformation at run time ?

[christianwimmer]

Truffle is most likely not what you want, because then your application is no longer AOT compiled.

[yswdqz]

I understand. For my case, it might be better to write a class to implement org.graalvm.nativeimage.hosted.Feature to add the transformed classes to the predefined-class list?

[vjovanov]

The bytecode transformation is best done by passing a Java agent at build time with -J-javaagent:agent.jar to native-image. There are a few things to note:

• The agent is running and transforming all classes at build time.
• The agent should not touch the classes that are used by native-image itself. One can get in trouble then as unpredictable things can happen.
• The premain of the agent will be executed at build time.
• The agent is currently marked as link-at-build-time so all of the classes need to be present in the agent jar.

If you encounter issues please contact me via our community Slack.