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Remove "dangling" terminology for zero-sized pointees. (#262)

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* Update safety comment on BoxBytes pointer field.

* Update mentions of "dangling" pointers elsewhere in src/allocation.rs.
This commit is contained in:
zachs18 2024-08-11 07:59:50 +00:00 committed by GitHub
parent 5eecd33318
commit bb62be5baa
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1 changed files with 12 additions and 10 deletions
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22
src/allocation.rs
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@ -68,9 +68,10 @@ pub fn try_cast_box<A: NoUninit, B: AnyBitPattern>(
#[inline]
pub fn try_zeroed_box<T: Zeroable>() -> Result<Box<T>, ()> {
if size_of::<T>() == 0 {
// This will not allocate but simply create a dangling pointer.
let dangling = core::ptr::NonNull::dangling().as_ptr();
return Ok(unsafe { Box::from_raw(dangling) });
// This will not allocate but simply create an arbitrary non-null
// aligned pointer, valid for Box for a zero-sized pointee.
let ptr = core::ptr::NonNull::dangling().as_ptr();
return Ok(unsafe { Box::from_raw(ptr) });
}
let layout = Layout::new::<T>();
let ptr = unsafe { alloc_zeroed(layout) };
@ -125,10 +126,11 @@ pub fn try_zeroed_slice_box<T: Zeroable>(
length: usize,
) -> Result<Box<[T]>, ()> {
if size_of::<T>() == 0 || length == 0 {
// This will not allocate but simply create a dangling slice pointer.
let dangling = core::ptr::NonNull::dangling().as_ptr();
let dangling_slice = core::ptr::slice_from_raw_parts_mut(dangling, length);
return Ok(unsafe { Box::from_raw(dangling_slice) });
// This will not allocate but simply create an arbitrary non-null aligned
// slice pointer, valid for Box for a zero-sized pointee.
let ptr = core::ptr::NonNull::dangling().as_ptr();
let slice_ptr = core::ptr::slice_from_raw_parts_mut(ptr, length);
return Ok(unsafe { Box::from_raw(slice_ptr) });
}
let layout = core::alloc::Layout::array::<T>(length).map_err(|_| ())?;
let ptr = unsafe { alloc_zeroed(layout) };
@ -742,9 +744,9 @@ impl<I: ?Sized, T: ?Sized + TransparentWrapper<I>> TransparentWrapperAlloc<I>
/// As `Box<[u8]>`, but remembers the original alignment.
pub struct BoxBytes {
// SAFETY: `ptr` is owned, points to `layout.size()` initialized bytes, and
// was allocated with `layout` (unless `layout.size() == 0` in which case it
// is dangling).
// SAFETY: `ptr` is aligned to `layout.align()`, points to
// `layout.size()` initialized bytes, and, if `layout.size() > 0`,
// is owned and was allocated with the global allocator with `layout`.
ptr: NonNull<u8>,
layout: Layout,
}