8358694: VM asserts if CodeCacheSegmentSize is not a power of 2 by offamitkumar · Pull Request #25708 · openjdk/jdk

offamitkumar · 2025-06-10T04:46:43Z

Makes sure that JVM exits gracefully when CodeCacheSegmentSize is not a power of 2.

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Change must be properly reviewed (1 review required, with at least 1 Reviewer)
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Issue

JDK-8358694: VM asserts if CodeCacheSegmentSize is not a power of 2 (Bug - P4)

Reviewers

Damon Fenacci (@dafedafe - Committer) Review applies to 2db6f325
Aleksey Shipilev (@shipilev - Reviewer)

Reviewing

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$ git checkout pull/25708

Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk.git pull/25708/head

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bridgekeeper · 2025-06-10T04:47:16Z

👋 Welcome back amitkumar! 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 · 2025-06-10T04:48:08Z

@offamitkumar 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:

8358694: VM asserts if CodeCacheSegmentSize is not a power of 2

Reviewed-by: shade, dfenacci

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 6 new commits pushed to the master branch:

fdfc557: 8360131: Remove use of soon-to-be-removed APIs by CTW framework
54fec2b: 8360220: Deprecate and obsolete ParallelRefProcBalancingEnabled
03d66d9: 8358572: C1 hits "need debug information" assert with -XX:-DeoptC1
... and 3 more: https://git.openjdk.org/jdk/compare/34412da52b41e9374168e67e3b6129576c8e4402...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.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

openjdk · 2025-06-10T04:48:44Z

@offamitkumar The following label will be automatically applied to this pull request:

hotspot-compiler

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

mlbridge · 2025-06-10T04:51:39Z

Webrevs

dafedafe

Thanks for fixing this @offamitkumar!
I was wondering if we couldn't do this right at the start when we check the flag constraints, e.g. here:

jdk/src/hotspot/share/runtime/flags/jvmFlagConstraintsCompiler.cpp

Line 158 in ca7b885

JVMFlag::Error CodeCacheSegmentSizeConstraintFunc(uintx value, bool verbose) {

shipilev

There is already CodeCacheSegmentSizeConstraintFunc that verifies the flag values. Move the check there?

offamitkumar · 2025-06-10T08:41:51Z

Thanks for the suggestion. I have moved the changes to the constraints specific file (I didn't know that this file exists, So missed it).

Please have another look. @shipilev @dafedafe

Thanks.

shipilev

Looks okay to me. Compiler folk should take a look as well.

dafedafe · 2025-06-11T06:20:40Z

Running Tier1-3+ tests...
The tests passed.

dafedafe · 2025-06-11T15:02:12Z

I might be a bit picky (sorry for that) but since the flag was triggering a crash I was wondering if we could have a small regression test to make sure the VM never crashes (possibly checking the error as well).

offamitkumar · 2025-06-16T04:04:44Z

@dafedafe can you have a look again ? I have added the testcase.

dafedafe

Thanks for adding the test @offamitkumar.

dafedafe · 2025-06-16T06:35:57Z

+
+public class CodeCacheSegmentSizeTest {
+    public static void main(String[] args) throws Exception {
+        String codeCacheSegmentSize = (Platform.isS390x() ? "67" : "36"); // invalid value (not power of two)


I think we can check it with any platform (it is not a S390-only constraint). Maybe we could also do it twice, once with and once without a power-of-two size. What do you think?

Maybe we could also do it twice, once with and once without a power-of-two size. What do you think?

That was a great suggestion. updated;

dafedafe

Thanks for changing the test @offamitkumar.

dafedafe · 2025-06-16T10:48:20Z

+
+        OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+        output.shouldContain("openjdk version"); // typical first line


The test fails here for me (the output has the string "java version", not "openjdk version").
Maybe instead of checking this string we could check that there is no error?

This was the string for me:

amit@a3560042:~/jdk$ ./build/linux-s390x-server-fastdebug/jdk/bin/java -XX:+UnlockExperimentalVMOptions -XX:CodeCacheSegmentSize=64 -version openjdk version "26-internal" 2026-03-17 OpenJDK Runtime Environment (fastdebug build 26-internal-adhoc.amit.jdk) OpenJDK 64-Bit Server VM (fastdebug build 26-internal-adhoc.amit.jdk, mixed mode) amit@a3560042:~/jdk$

But I will update it and check for error only.

dafedafe · 2025-06-16T10:48:59Z

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2024 IBM Corporation. All rights reserved.


Suggested change

* Copyright (c) 2024 IBM Corporation. All rights reserved.

* Copyright (c) 2025 IBM Corporation. All rights reserved.

offamitkumar · 2025-06-18T04:34:10Z

@dafedafe do you have further requests :)

dafedafe

Looks good to me. Thanks again @offamitkumar!

offamitkumar · 2025-06-18T10:13:00Z

Thanks @dafedafe, @shipilev for the reviews.

/integrate

openjdk · 2025-06-18T10:14:03Z

@offamitkumar This pull request has not yet been marked as ready for integration.

offamitkumar · 2025-06-18T10:14:21Z

Oh, sorry, I mistook Damon as reviewer. My mistake.

shipilev

Looks okay.

offamitkumar · 2025-06-25T04:38:02Z

Thanks again for the reviews.

/integrate

openjdk · 2025-06-25T04:39:08Z

Going to push as commit 263e32b.
Since your change was applied there have been 20 commits pushed to the master branch:

7d6c902: 8357726: Improve C2 to recognize counted loops with multiple casts in trip counter
5091057: 8351010: Test java/io/File/GetXSpace.java failed: / usable space 56380809216 > free space 14912244940
ba0c122: 8359808: JavaRuntimeURLConnection should only connect to non-directory resources
... and 17 more: https://git.openjdk.org/jdk/compare/34412da52b41e9374168e67e3b6129576c8e4402...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-06-25T04:39:16Z

@offamitkumar Pushed as commit 263e32b.

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

make jvm exit gracefully

55af21f

offamitkumar marked this pull request as ready for review June 10, 2025 04:47

openjdk Bot changed the title ~~8358694~~ 8358694: VM asserts if CodeCacheSegmentSize is not a power of 2 Jun 10, 2025

openjdk Bot added the rfr Pull request is ready for review label Jun 10, 2025

openjdk Bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Jun 10, 2025

dafedafe reviewed Jun 10, 2025

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shipilev suggested changes Jun 10, 2025

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offamitkumar added 2 commits June 10, 2025 08:35

move the changes in flag constraints specific file

8e3688f

fix

539b3fe

shipilev approved these changes Jun 10, 2025

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openjdk Bot added the ready Pull request is ready to be integrated label Jun 10, 2025

offamitkumar requested a review from dafedafe June 11, 2025 04:41

add test case

d7aef4a

openjdk Bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jun 12, 2025

offamitkumar added 2 commits June 12, 2025 05:07

fix comment

f8fbb4d

remove whitespace

24511b0

openjdk Bot added the rfr Pull request is ready for review label Jun 12, 2025

dafedafe reviewed Jun 16, 2025

View reviewed changes

updates testcase

520e351

dafedafe reviewed Jun 16, 2025

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remove string check & update copyright header

2db6f32

dafedafe approved these changes Jun 18, 2025

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offamitkumar requested a review from shipilev June 18, 2025 10:14

offamitkumar added 2 commits June 24, 2025 09:27

Merge branch 'master' into codecache

41cc96e

uintx to size_t

a8437a4

shipilev approved these changes Jun 24, 2025

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openjdk Bot added the ready Pull request is ready to be integrated label Jun 24, 2025

openjdk Bot added the integrated Pull request has been integrated label Jun 25, 2025

openjdk Bot closed this Jun 25, 2025

openjdk Bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jun 25, 2025


		OutputAnalyzer output = new OutputAnalyzer(pb.start());

		output.shouldContain("openjdk version"); // typical first line

		@@ -0,0 +1,79 @@
		/*
		* Copyright (c) 2024 IBM Corporation. All rights reserved.

	* Copyright (c) 2024 IBM Corporation. All rights reserved.
	* Copyright (c) 2025 IBM Corporation. All rights reserved.

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