Since rust-lang/reference#1387 and #117572, &raw mut (*p).field/addr_of!((*p).field) is defined to have the same inbounds preconditions as ptr::offset/ptr::byte_offset. I.e. &raw const (*p).field does not require that p: *const T point to a full size_of::<T>() bytes of memory, only that p.byte_add(offset_of!(T, field)) is defined.

The old comment "[...] we don't even get to use &raw const (*entry_ptr).d_name because that operation requires the full extent of *entry_ptr to be in bounds of the same allocation, which is not necessarily the case here [...]" is now outdated, and the code can be simplified to use &raw const (*entry_ptr).field.

There should be no behavior differences from this PR.

The : *const dirent64 on line 716 and the const _: usize = mem::offset_of!(dirent64, $field); and comment on lines 749-751 are just sanity checks and should not affect semantics.

Since the offset_ptr! macro is only called three times, and all with the same local variable entry_ptr, I just used the local variable directly in the macro instead of taking it as an input, and renamed the macro to entry_field_ptr!.

The whole macro could also be removed and replaced with just using &raw const (*entry_ptr).field in the three places, but the comments on the macro seemed worthwhile to keep.