8341471: Reversed field layout caused by unstable sorting #21382

fg1417 · 2024-10-07T08:55:17Z

For class Test:

    public class Test {
        char a000;
        char a001;
        char a002;
        char a003;
        char a004;
        char a005;
        char a006;
        char a007;
        char a008;
        char a009;
        char a00a;
        char a00b;
    }

We found its field layout on macOS was:

Layout of class Test
  Instance fields:
   @0 12/- RESERVED
   @12 "a00b" C 2/2 REGULAR
   @14 "a001" C 2/2 REGULAR
   @16 "a002" C 2/2 REGULAR
   @18 "a003" C 2/2 REGULAR
   @20 "a004" C 2/2 REGULAR
   @22 "a005" C 2/2 REGULAR
   @24 "a006" C 2/2 REGULAR
   @26 "a007" C 2/2 REGULAR
   @28 "a008" C 2/2 REGULAR
   @30 "a009" C 2/2 REGULAR
   @32 "a00a" C 2/2 REGULAR
   @34 "a000" C 2/2 REGULAR

a000 was put in the end while a00b was put in the beginning.

Fields get sorted according to size in [1]. qsort() on macOS reverses the order of fields with the same size. We should extend the comparison function to preserve the order on macOS, as we did on Windows.

Tier 1-3 passed on macOS.

[1]

jdk/src/hotspot/share/classfile/fieldLayoutBuilder.cpp

Line 102 in 3ee94e0

void FieldGroup::sort_by_size() {

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Issue

JDK-8341471: Reversed field layout caused by unstable sorting (Bug - P4)

Reviewers

Julian Waters (@TheShermanTanker - Committer)
Johan Sjölen (@jdksjolen - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/21382/head:pull/21382
$ git checkout pull/21382

Update a local copy of the PR:
$ git checkout pull/21382
$ git pull https://git.openjdk.org/jdk.git pull/21382/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 21382

View PR using the GUI difftool:
$ git pr show -t 21382

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/21382.diff

Webrev

Link to Webrev Comment

@0

…ting For class Test: ``` public class Test { char a000; char a001; char a002; char a003; char a004; char a005; char a006; char a007; char a008; char a009; char a00a; char a00b; } ``` We found its field layout on macOS was: Layout of class Test Instance fields: @0 12/- RESERVED @12 "a00b" C 2/2 REGULAR @14 "a001" C 2/2 REGULAR @16 "a002" C 2/2 REGULAR @18 "a003" C 2/2 REGULAR @20 "a004" C 2/2 REGULAR @22 "a005" C 2/2 REGULAR @24 "a006" C 2/2 REGULAR @26 "a007" C 2/2 REGULAR @28 "a008" C 2/2 REGULAR @30 "a009" C 2/2 REGULAR @32 "a00a" C 2/2 REGULAR @34 "a000" C 2/2 REGULAR `a000` was put in the end while `a00b` was put in the beginning. Fields get sorted according to size in [1]. `qsort()` on macOS reverses the order of fields with the same size. We should extend the comparison function to preserve the order on macOS, as we did on Windows. Tier 1-3 passed on macOS. [1] https://github.com/openjdk/jdk/blob/3ee94e040a7395d11a294a6b660d707c97f188f8/src/hotspot/share/classfile/fieldLayoutBuilder.cpp#L102

bridgekeeper · 2024-10-07T08:56:08Z

👋 Welcome back fgao! 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 · 2024-10-07T08:56:24Z

@fg1417 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:

8341471: Reversed field layout caused by unstable sorting

Reviewed-by: jwaters, jsjolen

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 30 new commits pushed to the master branch:

d3f3c6a: 8330157: C2: Add a stress flag for bailouts
d809bc0: 8341658: RISC-V: Test DateFormatProviderTest.java run timeouted
de90204: 8341588: Remove CollectionUsageThreshold.java from ProblemList-Xcomp for debugging
f276f58: 8341803: ProblemList containers/docker/TestJcmdWithSideCar.java on linux-x64
7eab0a5: 8337066: Repeated call of StringBuffer.reverse with double byte string returns wrong result
62acc9c: 8341548: More concise use of classfile API
7312eea: 8341131: Some jdk/jfr/event/compiler tests shouldn't be executed with Xcomp
966eb72: 8341447: Open source closed frame tests # 5
b9db74a: 8341378: Open source few TrayIcon tests - Set8
6546353: 8340203: Link color is hard to distinguish from text color in API documentation
... and 20 more: https://git.openjdk.org/jdk/compare/28977972a0129892543222eada4dc99f4cd62574...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 · 2024-10-07T08:57:07Z

@fg1417 The following label will be automatically applied to this pull request:

hotspot-runtime

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 · 2024-10-07T09:00:13Z

Webrevs

TheShermanTanker

Not usually my domain, but this looks good since it's not that big of a change

theRealAph · 2024-10-07T09:23:37Z

src/hotspot/share/classfile/fieldLayoutBuilder.hpp

-#ifdef _WINDOWS
-    // qsort() on Windows reverse the order of fields with the same size
+#if defined (_WINDOWS) || defined (__APPLE__)
+    // qsort() on Windows/macOS reverse the order of fields with the same size
    // the extension of the comparison function below preserves this order


qsort() isn't defined to be stable anywhere. I can't see any reason to restrict thus bug fix to Windows and MacOS.

@theRealAph thanks for your review. The new commit removed the macro and applied the extension of the comparison function to all platforms. Tier 1 - 3 passed on both linux-aarch64 and x86 platforms.

jdksjolen

Please add a comment that mentions the reason for the branch, for example

// ensure stable sort
if (...) {

}

fg1417 · 2024-10-08T14:08:07Z

Please add a comment that mentions the reason for the branch, for example
// ensure stable sort
if (...) {

}

Thanks for your review @jdksjolen . Updated it with comments.

jdksjolen

LGTM

fg1417 · 2024-10-09T08:49:43Z

May I have a review for the latest commit? @theRealAph @TheShermanTanker

Thanks!

TheShermanTanker

In my opinion it was sufficient to use it only for macOS and Windows, but I don't mind it for all platforms

fg1417 · 2024-10-14T08:39:28Z

Thanks for your review @theRealAph @TheShermanTanker @jdksjolen .

I'll integrate it.

/integrate

openjdk · 2024-10-14T08:40:07Z

Going to push as commit dcac4b0.
Since your change was applied there have been 92 commits pushed to the master branch:

e3f6503: 8341893: AArch64: Micro-optimize compressed ptr decoding
037f11b: 8341708: Optimize safepoint poll encoding with smaller poll data offset
8d0975a: 8336726: C2: assert(!do_asserts || projs->fallthrough_ioproj != nullptr) failed: must be found
fe98f86: 8226938: [TEST_BUG]GTK L&F: There is no Details button in FileChooser Dialog
5c4f1ef: 8226933: [TEST_BUG]GTK L&F: There is no swatches or RGB tab in JColorChooser
41ee582: 8341138: Rename jtreg property docker.support as container.support
2e1c193: 8342003: ProblemList sun/security/tools/keytool/GenKeyPairSigner.java
2db3397: 8341797: Fix ExceptionOccurred in jdk.jdi
c4965d9: 8341794: Fix ExceptionOccurred in jdk.attach
3f53d57: 8340327: A common framework to support public key algorithms with standard parameter sets
... and 82 more: https://git.openjdk.org/jdk/compare/28977972a0129892543222eada4dc99f4cd62574...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-10-14T08:40:14Z

@fg1417 Pushed as commit dcac4b0.

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

openjdk bot added the rfr Pull request is ready for review label Oct 7, 2024

openjdk bot added the hotspot-runtime hotspot-runtime-dev@openjdk.org label Oct 7, 2024

TheShermanTanker approved these changes Oct 7, 2024

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theRealAph reviewed Oct 7, 2024

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fg1417 added 2 commits October 8, 2024 10:12

Merge branch 'master' into field_layout_fix

cb946c1

Extend the comparison function to all platforms

3034f28

fg1417 changed the title ~~8341471: [macOS_aarch64] Reversed field layout caused by unstable sorting~~ 8341471: Reversed field layout caused by unstable sorting Oct 8, 2024

jdksjolen reviewed Oct 8, 2024

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