8270098: ZGC: ZBarrierSetC2::clone_at_expansion fails with "Guard against surprises" assert

[TobiHartmann]

The fix for JDK-8268125 (PR 53) assumed that only dead code can have a clone array with an unknown array ptr type at expansion time. As TestObjectArrayClone::testCloneObject proves, that is not true because we can invoke Object::clone on any object, including arrays.

As a result, invoking Object::clone on an Object array leads to triggering the "Guard against surprises" assert in debug and to incorrectly using the T_LONG copy stub (without GC barriers) in product. I was not able to trigger a crash in product but a corresponding runtime check (see patch) triggered reliably.

The fix is to fall back to ZBarrierSetRuntime::clone if the array ptr type is unknown. I will backport this fix to JDK 17u.

Thanks,
Tobias

---

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Issue

• JDK-8270098: ZGC: ZBarrierSetC2::clone_at_expansion fails with "Guard against surprises" assert

Reviewers

• Nils Eliasson (@neliasso - Reviewer)
• Vladimir Kozlov (@vnkozlov - Reviewer)

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[TobiHartmann]

/label add hotspot-compiler

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@TobiHartmann
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Webrevs

• 00: Full (0e1bd4d0)

[neliasso]

Looks good!

[openjdk]

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

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

8270098: ZGC: ZBarrierSetC2::clone_at_expansion fails with "Guard against surprises" assert

Reviewed-by: neliasso, kvn

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At the time when this comment was updated there had been 2 new commits pushed to the master branch:

• a86ac0d: 8271939: Clean up primitive raw accessors in oopDesc
• b84a9c7: 8271956: AArch64: C1 build failed after JDK-8270947

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[TobiHartmann]

Thanks for the review, Nils!

[vnkozlov]

Good.

[TobiHartmann]

Thanks for the review, Vladimir!

[TobiHartmann]

/integrate

[openjdk]

Going to push as commit 2384e12.
Since your change was applied there have been 16 commits pushed to the master branch:

• d53d94b: 8271925: ZGC: Arraycopy stub passes invalid oop to load barrier
• 3b899ef: 8272168: some hotspot runtime/logging tests don't check exit code
• abdc107: 8270454: G1: Simplify region index comparison
• eb6f3fe: 8272169: runtime/logging/LoaderConstraintsTest.java doesn't build test.Empty
• 9654fd7: 8271892: mark hotspot runtime/PrintStringTableStats/PrintStringTableStatsTest.java test as ignoring external VM flags
• 843943c: 8263567: gtests don't terminate the VM safely
• 7fc99cf: 8225488: Examine ExecutableType.getReceiverType behavior when source receiver parameter is absent
• 4548677: 8268824: Remove unused jdk.accessibility APIs deprecated for removal in JDK 9
• b53828b: 8272047: java/nio/channels/FileChannel/Transfer2GPlus.java failed with Unexpected transfer size: 2147418112
• 41dc795: 8264792: The NumberFormat for locale sq_XK formats price incorrectly.
• ... and 6 more: https://git.openjdk.java.net/jdk/compare/38ff85c824750e7da66fd86f5bde1c4587e529c4...master

Your commit was automatically rebased without conflicts.

[openjdk]

@TobiHartmann Pushed as commit 2384e12.

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