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[6.0] IRGen: don't stack promote classes for which the layout has not a fixed size #74982

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Merged
merged 1 commit into from
Jul 8, 2024
Merged

[6.0] IRGen: don't stack promote classes for which the layout has not a fixed size #74982

merged 1 commit into from
Jul 8, 2024

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eeckstein
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@eeckstein eeckstein commented Jul 5, 2024 •
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  • Explanation: Fixes a mis-compile caused by stack promotion of classes. The reserved stack space was wrong for classes which are imported from another module and contain implementation-only C-imported stored properties. Those properties don't show up in the class layout and make the class not "fixed size". For other cases of not fixed-size classes (e.g. classes containing resilient properties) this was already checked with ClassLayout::isFixedLayout. But for this specific case a check with ClassLayout::isFixedSize is required.
  • Scope: Affects code using classes as described above
  • Risk: Low. The changes adds a simple bail-out condition for stack promotion
  • Testing: Tested by a test case
  • Issue: rdar://131067105
  • Reviewer: @slavapestov
  • Main branch PR: IRGen: don't stack promote classes for which the layout has not a fixed size #74969

@eeckstein
IRGen: don't stack promote classes for which the layout has not a fix…
728a5ec 
…ed size

In most cases this was already checked with `ClassLayout::isFixedLayout`. But for classes which are imported from another module and contain implementation-only C-imported stored properties, those properties don't show up in the class layout. Stack promoting such classes will reserve too less space on the stack which leads to all kind of memory corruption problems. The fix is to also check `ClassLayout::isFixedSize`, which returns false for such classes.

Fixes a miscompile
rdar://131067105
@eeckstein eeckstein requested a review from a team as a code owner July 5, 2024 07:35
@eeckstein eeckstein requested a review from aschwaighofer July 5, 2024 07:35
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@swift-ci test

@eeckstein eeckstein requested a review from slavapestov July 5, 2024 07:43
@eeckstein eeckstein merged commit 4b9e512 into swiftlang:release/6.0 Jul 8, 2024
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@eeckstein eeckstein deleted the fix-stack-promotion-6.0 branch July 8, 2024 06:37
@eeckstein eeckstein mentioned this pull request Jul 12, 2024
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@DougGregor DougGregor DougGregor approved these changes

@tbkka tbkka tbkka approved these changes

@aschwaighofer aschwaighofer Awaiting requested review from aschwaighofer

@slavapestov slavapestov Awaiting requested review from slavapestov

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@eeckstein @DougGregor @tbkka