8367689: Revert removal of several compilation-related vmStructs fields #27318

fandreuz · 2025-09-16T16:40:05Z

#23782 (JDK-8315488) removed several vmStructs fields. A small subset was used in Async-Profiler:

CiEnv* _env
CompileTask* _task
ciMethod* _method

I propose a small patch to bring them back. It helps third-party tools in building useful features on the JDK. For example, Async-Profiler uses these fields to display the current method being compiled in a compiler thread.

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Issue

JDK-8367689: Revert removal of several compilation-related vmStructs fields (Enhancement - P4)

Reviewers

Coleen Phillimore (@coleenp - Reviewer) Review applies to e8b7849d
Kevin Walls (@kevinjwalls - Reviewer)

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bridgekeeper · 2025-09-16T16:41:08Z

👋 Welcome back fandreuzzi! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2025-09-16T16:43:02Z

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

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

8367689: Revert removal of several compilation-related vmStructs fields

Reviewed-by: kevinw, coleenp

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 37 new commits pushed to the master branch:

a306f88: 8339791: Refactor MiscUndecorated/ActiveAWTWindowTest.java
a355edb: 8367278: Test compiler/startup/StartupOutput.java timed out after completion on Windows
91a9794: 8367366: Do not support -XX:+AOTClassLinking for dynamic CDS archive
... and 34 more: https://git.openjdk.org/jdk/compare/c7f014ed494409cdf9fc925fe98de08346606408...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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openjdk · 2025-09-16T16:43:54Z

@fandreuz The following labels will be automatically applied to this pull request:

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hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

mlbridge · 2025-09-16T16:47:29Z

Webrevs

coleenp · 2025-09-16T19:12:35Z

src/hotspot/share/runtime/vmStructs.cpp

+                                                                                                                                     \
+  nonstatic_field(CompilerThread,              _env,                                          ciEnv*)                                \
+  nonstatic_field(ciEnv,                       _task,                                         CompileTask*)                          \
+  c2_nonstatic_field(Compile,                  _method,                                       ciMethod*)                             \


It would be really easy for someone to notice that these aren't used and delete them again, and it's unfortunate that this macro has to be propagated throughout all the vmStructs macros. I can see some external tool needing CompilerThread env and ciEnv task (the current compile task) but maybe this can not need Compile::_method?

Instead of adding the c2 macros, can you change the code to have:

COMPILER2_PRESENT(nontstatic_field(Compile, _method, ciMethod*))
COMPILER2_PRESENT(declare_toplevel_type(Compile))
etc.

Add a comment that these fields are needed.

I can see some external tool needing CompilerThread env and ciEnv task (the current compile task) but maybe this can not need Compile::_method?

This is how we use Compile::_method in Async-Profiler:

VMMethod* compiledMethod() { const char* env = *(const char**) at(_comp_env_offset); if (env != NULL) { const char* task = *(const char**) (env + _comp_task_offset); if (task != NULL) { return *(VMMethod**) (task + _comp_method_offset); } } return NULL; }

so we can get a jmethodID to the method being compiled. That's the only use case we have for these fields.

@coleenp Good catch, thanks. Compile::_method is redundant, indeed. CompileTask::_method is what async-profiler needs, but it's still in place.
@fandreuz I think this PR can do without platform-dependent changes.

For the context, it's this feature that embeds method name of the current compile task right in the C1/C2 stack traces.

Good catch, thanks. Compile::_method is redundant,

I see, thanks! 3a263b3

I think this PR can do without platform-dependent changes.

Right, many things turned out to be unnecessary. Thanks

coleenp

Oh that is much better! Thanks.

fandreuz · 2025-09-17T08:20:26Z

Test failure seems unrelated: https://github.com/fandreuz/jdk/actions/runs/17780614141/job/50541594076#step:10:2426

albertnetymk · 2025-09-17T08:28:53Z

src/hotspot/share/runtime/vmStructs.cpp

     static_field(VMRegImpl,                   stack0,                                        VMReg)                                 \
                                                                                                                                     \
+  /**************/                                                                                                                   \
+  /* CI (NOTE: these fields should not be removed, they can be used by external tools) */                                            \


Can you also clarify what "external tools" are in the comment so that when/if those external tools stop using them, we can re-evaluate?

Do you mean I should explicitly mention Async-Profiler?

kevinjwalls · 2025-09-17T09:41:00Z

We should clarify:
These fields are not a public interface, but the JVM has to maintain them due to other software's expectations?

Async-Profiler is great, but is this change the right solution? Are there other fields which other software would have liked to stay around, and what else can not be removed?

Curious how did Async-Profiler break when these are removed? Is it a crash that Async-Profiler needs to workaround, or is there less information in the collected profile.

apangin · 2025-09-17T12:59:13Z

@kevinjwalls Right, VMStructs is not a public supported interface, the JVM is not obliged to maintain it. Yet, some external tools (async-profiler and eBPF based profilers) softly rely on that in the lack of standard supported alternatives. At the same time, we are improving OpenJDK built-in capabilities that can eventually serve as such an alternative. A recent example is JEP 509: JFR CPU-Time Profiling. It's still a long path until JFR or other built-in tools can satisfy today's demand; in the meantime, VMStructs provides a temporary solution.

VMStructs is a reasonable trade-off, very cheap from the maintenance perspective as opposed to AsyncGetCallTrace (async-profiler no longer depends on the latter). To emphasize, we do not expect others to maintain VM structures that async-profiler relies on, that is our (profiler + Corretto) responsibility. Infrequent changes will be small, localized and safe, like in this PR.

As for the question how async-profiler breaks: if it is an optional feature (like here), it gracefully reduces functionality. Async-profiler attempts to detect essential VM changes and fail fast to prevent from crashing at runtime.

kevinjwalls · 2025-09-17T14:02:48Z

Thanks @apangin Andrei

I thought we should be open and explicit about this, good to have that exchange in the review. Async-Profiler knew what it was getting into. 8-)

In the comment being added above, what is it appropriate to say...

Saying "should not removed... they can be used by external tools" as an instruction seems like an overreach. Maybe more like:

"These CI fields are retained in VMStructs for the benefit of external tools, to ease their migration to a future alternative."

kevinjwalls · 2025-09-18T08:00:37Z

src/hotspot/share/runtime/vmStructs.cpp

+  /* CI (NOTE: these CI fields are retained in VMStructs for the benefit of external tools, */                                       \
+  /* to ease their migration to a future alternative.                                       */                                       \
+  /******************************************************************************************/                                       \
+                                                                                                                                     \


oops just a missing close ), but yes other than that I think we're done 8-)

Thanks, fixed in d7c4db0

kevinjwalls

OK, thanks!

fandreuz · 2025-09-18T08:13:54Z

/integrate

openjdk · 2025-09-18T08:15:26Z

@fandreuz
Your change (at version d7c4db0) is now ready to be sponsored by a Committer.

kevinjwalls · 2025-09-18T08:23:48Z

/sponsor

openjdk · 2025-09-18T08:25:05Z

Going to push as commit 4c5e901.
Since your change was applied there have been 37 commits pushed to the master branch:

a306f88: 8339791: Refactor MiscUndecorated/ActiveAWTWindowTest.java
a355edb: 8367278: Test compiler/startup/StartupOutput.java timed out after completion on Windows
91a9794: 8367366: Do not support -XX:+AOTClassLinking for dynamic CDS archive
... and 34 more: https://git.openjdk.org/jdk/compare/c7f014ed494409cdf9fc925fe98de08346606408...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-09-18T08:25:17Z

@kevinjwalls @fandreuz Pushed as commit 4c5e901.

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

fandreuz · 2025-09-18T08:28:55Z

/backport jdk25u

openjdk · 2025-09-18T08:32:00Z

@fandreuz the backport was successfully created on the branch backport-fandreuz-4c5e901c-master in my personal fork of openjdk/jdk25u. To create a pull request with this backport targeting openjdk/jdk25u:master, just click the following link:

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Hi all,

This pull request contains a backport of commit 4c5e901c from the openjdk/jdk repository.

The commit being backported was authored by Francesco Andreuzzi on 18 Sep 2025 and was reviewed by Kevin Walls and Coleen Phillimore.

Thanks!

If you need to update the source branch of the pull then run the following commands in a local clone of your personal fork of openjdk/jdk25u:

$ git fetch https://github.com/openjdk-bots/jdk25u.git backport-fandreuz-4c5e901c-master:backport-fandreuz-4c5e901c-master
$ git checkout backport-fandreuz-4c5e901c-master
# make changes
$ git add paths/to/changed/files
$ git commit --message 'Describe additional changes made'
$ git push https://github.com/openjdk-bots/jdk25u.git backport-fandreuz-4c5e901c-master

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fandreuz added 3 commits September 16, 2025 15:39

bring back fields

b2a76ef

remove indent

5400dd0

ops

5bc13c6

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fandreuz marked this pull request as draft September 16, 2025 18:45

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coleenp suggested changes Sep 16, 2025

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fandreuz added 5 commits September 16, 2025 21:57

nn

3a263b3

nn

e15cbda

cc

f9cb18b

nn

8603beb

nn

3165277

fandreuz marked this pull request as ready for review September 16, 2025 22:19

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krk mentioned this pull request Sep 22, 2025

ComptaskTests.testCompTask is broken in JDK 25 async-profiler/async-profiler#1501

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8367689: Revert removal of several compilation-related vmStructs fields #27318

8367689: Revert removal of several compilation-related vmStructs fields #27318

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