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[pointer][WIP] Transmute #2408

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[pointer][WIP] Transmute #2408

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@joshlf joshlf commented Feb 28, 2025 •
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@joshlf joshlf force-pushed the Iad14813bc6d933312bc8d7a1ddcf1aafc7126938 branch from bd18425 to 4bd4fd9 Compare February 28, 2025 23:09
@joshlf joshlf force-pushed the Ie66db9044be1dc310a6b7280a73652a357878376 branch from feb5ccf to 03547a1 Compare February 28, 2025 23:09
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joshlf commented Feb 28, 2025

I think we may have to handle UnsafeCell agreement after all. In particular, in order to implement TryFromBytes for atomics, we need to be able to go from e.g. Ptr<AtomicU8> to Ptr<UnsafeCell<u8>> so that we can call <UnsafeCell<u8> as TryFromBytes>::is_bit_valid. This will require care since this is unsound for shared aliasing. We know in practice that we'll always be using exclusive aliasing, but I'm not sure how to express that generically.

@joshlf joshlf force-pushed the Iad14813bc6d933312bc8d7a1ddcf1aafc7126938 branch from 4bd4fd9 to f1b2bec Compare March 2, 2025 23:21
@joshlf joshlf force-pushed the Ie66db9044be1dc310a6b7280a73652a357878376 branch from 03547a1 to 0c59508 Compare March 2, 2025 23:21
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joshlf commented Mar 2, 2025
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src/wrappers.rs Outdated
@@ -394,14 +394,14 @@ impl<T: Unaligned> Deref for Unalign<T> {

#[inline(always)]
fn deref(&self) -> &T {
Ptr::from_ref(self).transparent_wrapper_into_inner().bikeshed_recall_aligned().as_ref()
Ptr::from_ref(self).transmute().bikeshed_recall_aligned().as_ref()
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Bad news: This fails because it requires T: KnownLayout, which we wanted to avoid. We might be able to work around it with the SizedKnownLayout trick, or we might need to reconsider the T: KnownLayout bound.

@joshlf joshlf force-pushed the Iad14813bc6d933312bc8d7a1ddcf1aafc7126938 branch from 653cdb9 to 3e52166 Compare March 3, 2025 00:02
@joshlf joshlf force-pushed the Ie66db9044be1dc310a6b7280a73652a357878376 branch from 0c59508 to daf3a21 Compare March 3, 2025 00:02
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[pointer][WIP] Transmute
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gherrit-pr-id: Iad14813bc6d933312bc8d7a1ddcf1aafc7126938
@joshlf joshlf force-pushed the Iad14813bc6d933312bc8d7a1ddcf1aafc7126938 branch from 3e52166 to 3b22cad Compare March 3, 2025 17:44
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