[5.5] Concurrency: fix UB in DefaultActor initialization #40263
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This fixes a latent UB instance in the `DefaultActor` implementation that has haunted the Windows target. The shared constructor for the type caused an errant typo that happened to compile which introduced UB but happened to work for the non-Windows cases. This happened to work for the other targets as `swift::atomic` had a `std::atomic` at on most configurations, and the C delegate for the Actor initializer happened to overlap and initialize the memory properly. The Windows case used an inline pointer width value but would be attempted to be initialized as a `std::atomic`. Relying on the overlap is unsafe to assume, and we should use the type's own constructor which delegates appropriately.
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@swift-ci please test |
mikeash
approved these changes
Nov 19, 2021
compnerd
changed the title
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Cherry-picked from #40260 |
tkremenek
approved these changes
Dec 3, 2021
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This fixes a latent UB instance in the
DefaultActorimplementationthat has haunted the Windows target. The shared constructor for the
type caused an errant typo that happened to compile which introduced
UB but happened to work for the non-Windows cases. This happened to
work for the other targets as
swift::atomichad astd::atomicaton most configurations, and the C delegate for the Actor initializer
happened to overlap and initialize the memory properly. The Windows
case used an inline pointer width value but would be attempted to be
initialized as a
std::atomic. Relying on the overlap is unsafe toassume, and we should use the type's own constructor which delegates
appropriately.
Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.
Resolves SR-NNNN.