8300800: UB: Shift exponent 32 is too large for 32-bit type 'int' #20530

afshin-zafari · 2024-08-09T17:54:17Z

The operand of shift which is a constant 0 changed to unsigned long.

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Issue

JDK-8300800: UB: Shift exponent 32 is too large for 32-bit type 'int' (Bug - P4)

Reviewers

Gerard Ziemski (@gerard-ziemski - Committer) 🔄 Re-review required (review applies to 9143adaf)
Kim Barrett (@kimbarrett - Reviewer)
Andrew Dinn (@adinn - Reviewer)

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bridgekeeper · 2024-08-09T17:55:12Z

👋 Welcome back azafari! 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 · 2024-08-09T17:55:55Z

@afshin-zafari 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:

8300800: UB: Shift exponent 32 is too large for 32-bit type 'int'

Reviewed-by: kbarrett, adinn, gziemski

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:

41e31d6: 8337622: IllegalArgumentException in java.lang.reflect.Field.get
2ca136a: 8337815: Relax G1EvacStats atomic operations
99edb4a: 8337702: Use new ForwardExceptionNode to call StubRoutines::forward_exception_entry()
8d08314: 8337795: Type annotation attached to incorrect type during class reading
f84240b: 8338011: CDS archived heap object support for 64-bit Windows
04b146a: 8337334: Test tools/javac/7142086/T7142086.java timeout with fastdebug binary
a36fb36: 8338108: Give better error message in configure if a full XCode is missing
61d1dc5: 8334466: Ambiguous method call with generics may cause FunctionDescriptorLookupError
89a15f1: 8337681: PNGImageWriter uses much more memory than necessary
a6c0630: 8337938: ZUtils::alloc_aligned allocates without reporting to NMT
... and 27 more: https://git.openjdk.org/jdk/compare/4b740d87ee50ba49305add4aae6490bebb6963ba...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 · 2024-08-09T17:57:15Z

@afshin-zafari 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 · 2024-08-09T18:00:01Z

Webrevs

01: Full - Incremental (69033fa7)
00: Full (9143adaf)

gerard-ziemski

LGTM, thanks!

kimbarrett

This should use UCONST64 instead of a UL suffix, because that suffix is
platform-dependent. Windows is LLP64, so L is 32 bits. This is code that is
(probably, I haven't checked for sure) used by the windows-aarch64 port.

kimbarrett · 2024-08-11T04:51:55Z

src/hotspot/cpu/aarch64/immediate_aarch64.cpp

@@ -295,7 +295,7 @@ static int expandLogicalImmediate(uint32_t immN, uint32_t immr,
    uint64_t and_bits_sub = replicate(and_bit, 1, nbits);
    uint64_t or_bits_sub = replicate(or_bit, 1, nbits);
    uint64_t and_bits_top = (and_bits_sub << nbits) | ones(nbits);
-    uint64_t or_bits_top = (0 << nbits) | or_bits_sub;
+    uint64_t or_bits_top = (0UL << nbits) | or_bits_sub;


This should use UCONST64 instead of a UL suffix, because that suffix is platform-dependent. Windows is
LLP64, so L is 32 bits. This is code that is (probably, I haven't checked for sure) used by the windows-aarch64
port.

adinn

Kim is correct that this code is needed for Windows/aarch64. Hence that it should use UCONST64(0).

kimbarrett · 2024-08-12T09:23:24Z

src/hotspot/cpu/aarch64/immediate_aarch64.cpp

@@ -295,7 +295,7 @@ static int expandLogicalImmediate(uint32_t immN, uint32_t immr,
    uint64_t and_bits_sub = replicate(and_bit, 1, nbits);
    uint64_t or_bits_sub = replicate(or_bit, 1, nbits);
    uint64_t and_bits_top = (and_bits_sub << nbits) | ones(nbits);
-    uint64_t or_bits_top = (0 << nbits) | or_bits_sub;
+    uint64_t or_bits_top = (UCONST64(0) << nbits) | or_bits_sub;


I focused on the UL suffix earlier, and didn't really think about what this is doing. Why are we shifting
a zero value at all? This equivalent to uint64_t or_bits_top = or_bits_sub;.

I believe this question came up in an earlier thread and was answered by @theRealAph. The shift of zero is there to emphasise continuity of this case with other cases where a non-zero value is shifted i.e. it serves to emphasize/document the connection between this implementation and the algorithm that it embodies.

Thanks for the background. It still looks weird and I can't unsee it now. But a comment might be almost
as intrusive to readability. So okay.

kimbarrett

Looks good.

kimbarrett · 2024-08-12T18:37:04Z

src/hotspot/cpu/aarch64/immediate_aarch64.cpp

@@ -295,7 +295,7 @@ static int expandLogicalImmediate(uint32_t immN, uint32_t immr,
    uint64_t and_bits_sub = replicate(and_bit, 1, nbits);
    uint64_t or_bits_sub = replicate(or_bit, 1, nbits);
    uint64_t and_bits_top = (and_bits_sub << nbits) | ones(nbits);
-    uint64_t or_bits_top = (0 << nbits) | or_bits_sub;
+    uint64_t or_bits_top = (UCONST64(0) << nbits) | or_bits_sub;


Thanks for the background. It still looks weird and I can't unsee it now. But a comment might be almost
as intrusive to readability. So okay.

afshin-zafari · 2024-08-13T16:23:55Z

Thank you @kimbarrett and @adinn for your comments.
/integrate

openjdk · 2024-08-13T16:25:44Z

Going to push as commit 21ca91e.
Since your change was applied there have been 54 commits pushed to the master branch:

58b9570: 8338142: (dc) DatagramChannelImpl.blockingReceive can use untimed-park when no timeout set
6af1d6f: 8335927: Revisit AnnotationConstantValueEntry and AnnotationValue.OfConstant
9e282e5: 8337998: CompletionFailure in getEnclosingType attaching type annotations
877fd5a: 8337595: Remove empty statements in src/hotspot/share/memory/metaspace
76e33b6: 8336148: Test runtime/locking/TestRecursiveMonitorChurn.java failed: Unexpected Inflation
ff8a9f9: 8337318: Deoptimization::relock_objects fails assert(monitor->owner() == Thread::current()) failed: must be
fbe4cc9: 8336384: AbstractQueuedSynchronizer.acquire should cancel acquire when failing due to a LinkageError or other errors
ba69ed7: 8338202: Shenandoah: Improve handshake closure labels
5bf2709: 8334475: UnsafeIntrinsicsTest.java#ZGenerationalDebug assert(!assert_on_failure) failed: Has low-order bits set
73f7a5f: 8338155: Fix -Wzero-as-null-pointer-constant warnings involving PTHREAD_MUTEX_INITIALIZER
... and 44 more: https://git.openjdk.org/jdk/compare/4b740d87ee50ba49305add4aae6490bebb6963ba...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-08-13T16:25:51Z

@afshin-zafari Pushed as commit 21ca91e.

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

8300800: UB: Shift exponent 32 is too large for 32-bit type 'int'

9143ada

openjdk bot added the rfr Pull request is ready for review label Aug 9, 2024

openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Aug 9, 2024

gerard-ziemski approved these changes Aug 9, 2024

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kimbarrett suggested changes Aug 11, 2024

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Used UCONST64(0) instead of UL.

69033fa

adinn approved these changes Aug 12, 2024

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8300800: UB: Shift exponent 32 is too large for 32-bit type 'int' #20530

8300800: UB: Shift exponent 32 is too large for 32-bit type 'int' #20530

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8300800: UB: Shift exponent 32 is too large for 32-bit type 'int' #20530

8300800: UB: Shift exponent 32 is too large for 32-bit type 'int' #20530

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