8304438: jcmd JVMTI.agent_load should obey EnableDynamicAgentLoading

[sspitsyn]

The VM option EnableDynamicAgentLoading was added in JDK 9, default true, to allow deployment to choose whether to allow agents to be loaded/started in the VM. The VM option does the right thing for tools using the Attach API but jcmd JVMTI.agent_load was missed. This should be fixed to disallow loading JVMTI agents when the EnableDynamicAgentLoading is false.

The CSR is:
JDK-8309250: jcmd JVMTI.agent_load should obey EnableDynamicAgentLoading

Testing:

• run new test test/jdk/sun/tools/jcmd/TestJcmdNoAgentLoad.java
• TBD: submit mach5 tiers 1-5 to make sure no new regressions are introduced

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change requires CSR request JDK-8309250 to be approved

Issues

• JDK-8304438: jcmd JVMTI.agent_load should obey EnableDynamicAgentLoading
• JDK-8309250: jcmd JVMTI.agent_load should obey EnableDynamicAgentLoading (CSR)

Reviewers

• Chris Plummer (@plummercj - Reviewer)
• Alan Bateman (@AlanBateman - Reviewer) ⚠️ Review applies to f82ce73e
• Alex Menkov (@alexmenkov - Reviewer)

Reviewing

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[openjdk]

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[AlanBateman]

/label remove core-libs

[openjdk]

@AlanBateman
The core-libs label was successfully removed.

[AlanBateman]

For the "load" command implemented in attachListener, do you remember why EnableDynamicAgentLoading is checked in attach_listener_thread_entry? Looking at it now, I wonder why the check isn't in load_agent. The code in attach_listener_thread_entry shouldn't have to special-case commands.

[sspitsyn]

Thank you for the comment.
I was also thinking if this check has to be done in one place.

[AlanBateman]

I was also thinking if this check has to be done in one place.

Yes, maybe JvmtiAgentList::load_agent, JvmtiAgent::load, or invoke_Agent_OnAttach. As part of the change to emit a warning when agent code is loaded into a running VM, invoke_Agent_OnAttach needs to check if EnableDynamicAgentLoading has been set on the command line, so looking at this VM option in one place would be nice.

[sspitsyn]

Yes, maybe JvmtiAgentList::load_agent, JvmtiAgent::load, or invoke_Agent_OnAttach. As part of the change to emit a warning when agent code is loaded into a running VM, invoke_Agent_OnAttach needs to check if EnableDynamicAgentLoading has been set on the command line, so looking at this VM option in one place would be nice.

I've moved the EnableDynamicAgentLoading check to the invoke_Agent_OnAttach.
It is the same place where a warning is going to be generated as part of the 8307478 (JEP enhancement).

[dholmes-ora]

A change in behaviour like this requires a CSR request - the code has been doing the wrong thing for a long time now!

/csr needed

[openjdk]

@dholmes-ora has indicated that a compatibility and specification (CSR) request is needed for this pull request.

@sspitsyn please create a CSR request for issue JDK-8304438 with the correct fix version. This pull request cannot be integrated until the CSR request is approved.

[sspitsyn]

A change in behaviour like this requires a CSR request - the code has been doing the wrong thing for a long time now!

Thank you for the comment. It was not fully clear if a CSR is needed in this case.
Created CSR (it is listed in the PR description).

[plummercj]

Except for the possible addition of some comments regarding what is meant by "loaded", the changes look good.

[plummercj]

Sorry, previous comment was for another review.

[plummercj]

Looks good.

[openjdk]

@sspitsyn This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8304438: jcmd JVMTI.agent_load should obey EnableDynamicAgentLoading

Reviewed-by: cjplummer, alanb, amenkov

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[AlanBateman]

Implementation change looks fine. Once your branch is sync up to main line then it should mean EnableDynamicAgentLoading is only used in one function, so easy to understand.

[sspitsyn]

/integrate

[openjdk]

Going to push as commit 4b15349.
Since your change was applied there has been 1 commit pushed to the master branch:

• b3c9d67: 8309136: [JVMCI] add -XX:+UseGraalJIT flag

Your commit was automatically rebased without conflicts.

[openjdk]

@sspitsyn Pushed as commit 4b15349.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

[sspitsyn]

Alan, Chris and Alex, thank you for review!