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Don't create references to uninitialized data in List::from_arena #87268

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Jul 19, 2021
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Don't create references to uninitialized data in List::from_arena #87268

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12 changes: 6 additions & 6 deletions compiler/rustc_middle/src/ty/list.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -63,17 +63,17 @@ impl<T: Copy> List<T> {

let (layout, _offset) =
Layout::new::<usize>().extend(Layout::for_value::<[T]>(slice)).unwrap();
let mem = arena.dropless.alloc_raw(layout);
let mem = arena.dropless.alloc_raw(layout) as *mut List<T>;
unsafe {
let result = &mut *(mem as *mut List<T>);
// Write the length
result.len = slice.len();
ptr::addr_of_mut!((*mem).len).write(slice.len());

// Write the elements
let arena_slice = slice::from_raw_parts_mut(result.data.as_mut_ptr(), result.len);
arena_slice.copy_from_slice(slice);
ptr::addr_of_mut!((*mem).data)
.cast::<T>()
.copy_from_nonoverlapping(slice.as_ptr(), slice.len());

result
&mut *mem
}
}

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