8300821: UB: Applying non-zero offset to non-null pointer 0xfffffffffffffffe produced null pointer

[tobiasholenstein]

"UndefinedBehaviorSanitizer" (https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html) in Xcode running on java --version discovered an Undefined Behavior. The reason is in the next() method

jdk/src/hotspot/share/asm/codeBuffer.cpp

Line 798 in 040f5b5

while (iter.next()) {

In RelocIterator::next() we get a nullpointer after _current++

jdk/src/hotspot/share/code/relocInfo.hpp

Line 612 in 040f5b5

_current++;

But this is actually expected: In the constructor of the iterator RelocIterator::RelocIterator we have

_current = cs->locs_start()-1;
_end     = cs->locs_end();

and in our case locs_start() and locs_end() are null - so _current is null-1. After _current++ both _end and _current are null. Just after _current++ we then check if _current == _end and return false (there is no next reloc info)

Solution

We want to be able to turn on "UndefinedBehaviorSanitizer" and don't have false positives. So we add a check
cs->has_locs() and only create the iterator if we have reloc info.

Also added a sanity check in RelocIterator::RelocIterator that checks that either both _current and _end are null or both are not null.

---

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

Issue

• JDK-8300821: UB: Applying non-zero offset to non-null pointer 0xfffffffffffffffe produced null pointer

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer)
• Tobias Hartmann (@TobiHartmann - Reviewer)

Reviewing

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Update a local copy of the PR:
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[bridgekeeper]

👋 Welcome back tholenstein! 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]

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[mlbridge]

Webrevs

• 00: Full (040f5b55)

[vnkozlov]

Good.

[openjdk]

@tobiasholenstein 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:

8300821: UB: Applying non-zero offset to non-null pointer 0xfffffffffffffffe produced null pointer

Reviewed-by: kvn, thartmann

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At the time when this comment was updated there had been 133 new commits pushed to the master branch:

• afda8fb: 8303136: MemoryPoolMBean/isCollectionUsageThresholdExceeded/isexceeded005 failed with "isCollectionUsageThresholdExceeded() returned true, while threshold = 1 and used = 0"
• 1d071d0: 8303690: Prefer ArrayList to LinkedList in com.sun.jmx.mbeanserver.Introspector
• 09d469e: 8252255: Blurry rendering of SwingNode with HiDPI scaling in JavaFX
• 21a6ab1: 8303799: [BACKOUT] JDK-8302801 Remove fdlibm C sources
• 5fa9bd4: 8302189: Mark assertion failures noreturn
• 9b10c69: 8303622: JFR: Missing message with Objects.requireNonNull
• d729824: 8286781: Replace the deprecated/obsolete gethostbyname and inet_addr calls
• 5f1108f: 8303151: DCmd framework cleanups
• 32f4d8b: 8303681: JFR: RemoteRecordingStream::setMaxAge() should accept null
• 9f9d678: 8302791: Add specific ClassLoader object to Proxy IllegalArgumentException message
• ... and 123 more: https://git.openjdk.org/jdk/compare/a2c5a4ac9ee10281470f291f5a8f8393acea02cc...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.

[TobiHartmann]

Looks good to me.

[tobiasholenstein]

thanks @vnkozlov and @TobiHartmann for the review!

/integrate

[openjdk]

Going to push as commit 01312a0.
Since your change was applied there have been 176 commits pushed to the master branch:

• 6d30bbe: 8303001: Add test for re-entrant upcalls
• de9f3b6: 8296400: pointCrlIssuers might be null in DistributionPointFetcher::verifyURL
• b9951dd: 8303820: Simplify type metadata
• 75d6306: 8303349: Simplify link format for generic types in index pages
• b1d89f3: 8294971: jdk.jlink jdk.tools.jimage.JImageTask is using ASM to verify classes
• 0f26d09: 8303822: gtestMain should give more helpful output
• e26cc52: 8303624: The java.lang.Thread.FieldHolder can be null for JNI attaching threads
• d06308c: 8302360: Atomic*.compareAndExchange Javadoc unclear
• 8b740b4: 8302779: HelidonAppTest.java fails with "assert(_cb == CodeCache::find_blob(pc())) failed: Must be the same" or SIGSEGV
• 562c8fc: 8303691: Fedora based devkit build should load more packages from archive location
• ... and 166 more: https://git.openjdk.org/jdk/compare/a2c5a4ac9ee10281470f291f5a8f8393acea02cc...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tobiasholenstein Pushed as commit 01312a0.

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