Fix unsafe AtomicRefCell<T> transmutes in Layout component #16833
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| // Required alignment in 32 bit architectures for safe | ||
| // transmute between PersistentLayoutData and PartialPersistentLayoutData. | ||
| #[cfg(target_pointer_width = "32")] _align: u64 |
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Why not have this dummy field unconditionally?
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Or, better yet, make it a [u64; 0], which affects alignment without size penalties.
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I did that way as a size optimization. Do you think that it isn't worth it?
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@emilio nice! I didn't know that
…y alignment differences
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Nice one @emilio, for @bors-servo r+ |
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📌 Commit 593e890 has been approved by |
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Fix unsafe AtomicRefCell<T> transmutes in Layout component <!-- Please describe your changes on the following line: --> Fixes unsafe transmute between `AtomicRefCell<PersistentLayoutData>` and `AtomicRefCell<PartialPersistentLayoutData>` which have different memory alignment in 32 bit archs leading to SEGV crashes. See #16817 and #16816 mem::align_of values in 32 bit archs (e.g. Android): ``` PersistentLayoutData 8 PersistentLayoutData 4 AtomicRefCell<PersistentLayoutData> 8 AtomicRefCell<PartialPersistentLayoutData> 4 ``` mem::align_of values in 64 bit archs ``` PersistentLayoutData 8 PersistentLayoutData 8 AtomicRefCell<PersistentLayoutData> 8 AtomicRefCell<PartialPersistentLayoutData> 8 ``` --- <!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: --> - [x] `./mach build -d` does not report any errors - [x] `./mach test-tidy` does not report any errors - [x] These changes fix #16817 (github issue number if applicable). <!-- Either: --> - [x] There are tests for these changes OR - [ ] These changes do not require tests because _____ <!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.--> <!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. --> <!-- Reviewable:start --> --- This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16833) <!-- Reviewable:end -->
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☀️ Test successful - android, arm32, arm64, linux-dev, linux-rel-css, linux-rel-wpt, mac-dev-unit, mac-rel-css, mac-rel-wpt1, mac-rel-wpt2, windows-msvc-dev |
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Fixes unsafe transmute between
AtomicRefCell<PersistentLayoutData>andAtomicRefCell<PartialPersistentLayoutData>which have different memory alignment in 32 bit archs leading to SEGV crashes. See #16817 and #16816mem::align_of values in 32 bit archs (e.g. Android):
mem::align_of values in 64 bit archs
./mach build -ddoes not report any errors./mach test-tidydoes not report any errorsThis change is