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constrain safety preconditions of layout_for_ptr functionality #117185

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constrain safety preconditions of layout_for_ptr functionality #117185

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4 changes: 4 additions & 0 deletions library/core/src/alloc/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -181,10 +181,14 @@ impl Layout {
/// - a [slice], then the length of the slice tail must be an initialized
/// integer, and the size of the *entire value*
/// (dynamic tail length + statically sized prefix) must fit in `isize`.
/// The pointer address plus the size of the entire value must not
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/// overflow the address space.
/// - a [trait object], then the vtable part of the pointer must point
/// to a valid vtable for the type `T` acquired by an unsizing coercion,
/// and the size of the *entire value*
/// (dynamic tail length + statically sized prefix) must fit in `isize`.
/// The pointer address plus the size of the entire value must not
/// overflow the address space.
/// - an (unstable) [extern type], then this function is always safe to
/// call, but may panic or otherwise return the wrong value, as the
/// extern type's layout is not known. This is the same behavior as
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12 changes: 10 additions & 2 deletions library/core/src/mem/mod.rs
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Expand Up @@ -359,10 +359,13 @@ pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
/// - a [slice], then the length of the slice tail must be an initialized
/// integer, and the size of the *entire value*
/// (dynamic tail length + statically sized prefix) must fit in `isize`.
/// The pointer address plus the size of the entire value must not
/// overflow the address space.
/// - a [trait object], then the vtable part of the pointer must point
/// to a valid vtable acquired by an unsizing coercion, and the size
/// of the *entire value* (dynamic tail length + statically sized prefix)
/// must fit in `isize`.
/// must fit in `isize`. The pointer address plus the size of the entire
/// value must not overflow the address space.
/// - an (unstable) [extern type], then this function is always safe to
/// call, but may panic or otherwise return the wrong value, as the
/// extern type's layout is not known. This is the same behavior as
Expand Down Expand Up @@ -506,10 +509,15 @@ pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
/// - a [slice], then the length of the slice tail must be an initialized
/// integer, and the size of the *entire value*
/// (dynamic tail length + statically sized prefix) must fit in `isize`.
/// The pointer address plus the size of the entire value must not
/// overflow the address space. The value one-past-the-end of this range
/// must also be within the address space.
/// - a [trait object], then the vtable part of the pointer must point
/// to a valid vtable acquired by an unsizing coercion, and the size
/// of the *entire value* (dynamic tail length + statically sized prefix)
/// must fit in `isize`.
/// must fit in `isize`. The pointer address plus the size of the entire
/// value must not overflow the address space. The value one-past-the-end
/// of this range must also be within the address space.
/// - an (unstable) [extern type], then this function is always safe to
/// call, but may panic or otherwise return the wrong value, as the
/// extern type's layout is not known. This is the same behavior as
Expand Down
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