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<[T]>::reverse: Fix pointer provenance rules #78816

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Merged
bors merged 1 commit into from
Nov 22, 2020
Merged

<[T]>::reverse: Fix pointer provenance rules #78816

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15 changes: 9 additions & 6 deletions library/core/src/slice/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -605,8 +605,9 @@ impl<T> [T] {
// many bytes away from the end of `self`.
// - Any initialized memory is valid `usize`.
unsafe {
let pa: *mut T = self.get_unchecked_mut(i);
let pb: *mut T = self.get_unchecked_mut(ln - i - chunk);
let ptr = self.as_mut_ptr();
let pa = ptr.add(i);
let pb = ptr.add(ln - i - chunk);
let va = ptr::read_unaligned(pa as *mut usize);
let vb = ptr::read_unaligned(pb as *mut usize);
ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
Expand Down Expand Up @@ -635,8 +636,9 @@ impl<T> [T] {
// always respected, ensuring the `pb` pointer can be used
// safely.
unsafe {
let pa: *mut T = self.get_unchecked_mut(i);
let pb: *mut T = self.get_unchecked_mut(ln - i - chunk);
let ptr = self.as_mut_ptr();
let pa = ptr.add(i);
let pb = ptr.add(ln - i - chunk);
let va = ptr::read_unaligned(pa as *mut u32);
let vb = ptr::read_unaligned(pb as *mut u32);
ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
Expand All @@ -654,8 +656,9 @@ impl<T> [T] {
// aligned, and can be read from and written to.
unsafe {
// Unsafe swap to avoid the bounds check in safe swap.
let pa: *mut T = self.get_unchecked_mut(i);
let pb: *mut T = self.get_unchecked_mut(ln - i - 1);
let ptr = self.as_mut_ptr();
let pa = ptr.add(i);
let pb = ptr.add(ln - i - 1);
ptr::swap(pa, pb);
}
i += 1;
Expand Down