315215 2026-05-20 11:36:49 -0700 REGRESSION(310262@main): [lldb] dump_class_layout_unittest.serial_test_InheritsFromClassWithPaddedBitfields fails constantly across all platforms. 2026-05-25 17:34:01 -0700 1 1 1 Unclassified WebKit New Bugs WebKit Nightly Build Unspecified Unspecified NEW InRadar P2 Normal --- 310442 1 d_delatoba ddkilzer ddkilzer simon.fraser webkit-bot-watchers-bugzilla webkit-bug-importer oldest_to_newest 2212611 0 d_delatoba 2026-05-20 11:36:49 -0700 Summary: dump_class_layout_unittest.TestDumpClassLayout.serial_test_InheritsFromClassWithPaddedBitfields (Tools/lldb/dump_class_layout_unittest.py:373) has been failing continuously on post-commit since 310262@main. LOG/Trace: https://build.webkit.org/#/builders/1716/builds/4051/steps/26/logs/stdio DIFF: Expected: Total byte size: 24 Total pad bytes: 14 Padding 61.98 % derivedBitfield @ +16 Actual: Total byte size: 16 Total pad bytes: 6 Padding 42.97 % derivedBitfield @ +10 TRACE: [9/48] dump_class_layout_unittest.TestDumpClassLayout.serial_test_InheritsFromClassWithPaddedBitfields failed: Traceback (most recent call last):' File "Volumes/Data/worker/Apple-Tahoe-Release-AppleSilicon-WK2-Tests/build/Tools/11db/dump_class_layout_unittest.py", line 397, in serial_test_InheritsFromClassWithPadd self. assertEqual(EXPECTED_RESULT, actual_layout.as_string()) AssertionError: +0 < 24> InheritsFromClassWithPaddedBitfields\[834 chars]98%' != ' +0 < 16› InheritsFromClassWithPaddedBitfields\[798 chars]97 %' +0 < 24> InheritsFromClassWithPaddedBitfields +0 < 16> InheritsFromClassWithPaddedBitfields ? +0 +0 +1 +1 +1 +1 +1 +1 +2 +4 +8 +8 +9 +9 +10 +16 < 16> 1> : 1> : 1> : 2> :1> :2> :1> 1> 4> : 1> :9> : 1> : 5> 6> :1> ClassWithPaddedBitfields ClassWithPaddedBitfields bool boolMember unsigned int bitfieldl : 1 bool bitfield2: 1 unsigned int bitfield3 : 2 unsigned int bitfield4 : 1 unsigned long bitfield5 : 2 <UNUSED BITS: 1 bit› «PADDING: 1 bytes› int intMember unsigned int bitfield?: 1 unsigned int bitfield8: 9 bool bitfield9: 1 <UNUSED BITS: 5 bits› <PADDING: 6 bytes> bool derivedBitfield: 1 +10 < : 1> bool derivedBitfield: 1 ? ? +16 1 :7> +10 <:7> <UNUSED BITS: 7 bits› <UNUSED BITS: 7 bits› ? ? 17+ 1 > 11+ 7> <PADDING: 7 bytes> 5> <PADDING: 5 bytes> ? - Total byte size: 24 ? → Total byte size: 16 - Total pad bytes: 14 ? + Total pad bytes: 6 ? - Padding percentage: 61.98 %? + Padding percentage: 42.97 %? 2212612 1 webkit-bug-importer 2026-05-20 11:36:55 -0700 <rdar://problem/177546068> 2213952 2 ddkilzer 2026-05-25 17:30:47 -0700 Pull request: https://github.com/WebKit/WebKit/pull/65641