1 use core::cell::RefCell;
2 use core::mem::{self, MaybeUninit};
3 use core::num::NonZeroUsize;
6 use std::fmt::{Debug, Display};
9 fn test_const_from_raw_parts() {
10 const SLICE: &[u8] = &[1, 2, 3, 4];
11 const FROM_RAW: &[u8] = unsafe { &*slice_from_raw_parts(SLICE.as_ptr(), SLICE.len()) };
12 assert_eq!(SLICE, FROM_RAW);
14 let slice = &[1, 2, 3, 4, 5];
15 let from_raw = unsafe { &*slice_from_raw_parts(slice.as_ptr(), 2) };
16 assert_eq!(&slice[..2], from_raw);
27 let mut p = Pair { fst: 10, snd: 20 };
28 let pptr: *mut Pair = &mut p;
29 let iptr: *mut isize = pptr as *mut isize;
30 assert_eq!(*iptr, 10);
32 assert_eq!(*iptr, 30);
33 assert_eq!(p.fst, 30);
35 *pptr = Pair { fst: 50, snd: 60 };
36 assert_eq!(*iptr, 50);
37 assert_eq!(p.fst, 50);
38 assert_eq!(p.snd, 60);
40 let v0 = vec![32000u16, 32001u16, 32002u16];
41 let mut v1 = vec![0u16, 0u16, 0u16];
43 copy(v0.as_ptr().offset(1), v1.as_mut_ptr().offset(1), 1);
44 assert!((v1[0] == 0u16 && v1[1] == 32001u16 && v1[2] == 0u16));
45 copy(v0.as_ptr().offset(2), v1.as_mut_ptr(), 1);
46 assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 0u16));
47 copy(v0.as_ptr(), v1.as_mut_ptr().offset(2), 1);
48 assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 32000u16));
54 let p: *const isize = null();
57 let q = p.wrapping_offset(1);
58 assert!(!q.is_null());
60 let mp: *mut isize = null_mut();
61 assert!(mp.is_null());
63 let mq = mp.wrapping_offset(1);
64 assert!(!mq.is_null());
66 // Pointers to unsized types -- slices
67 let s: &mut [u8] = &mut [1, 2, 3];
68 let cs: *const [u8] = s;
69 assert!(!cs.is_null());
71 let ms: *mut [u8] = s;
72 assert!(!ms.is_null());
74 let cz: *const [u8] = &[];
75 assert!(!cz.is_null());
77 let mz: *mut [u8] = &mut [];
78 assert!(!mz.is_null());
80 let ncs: *const [u8] = null::<[u8; 3]>();
81 assert!(ncs.is_null());
83 let nms: *mut [u8] = null_mut::<[u8; 3]>();
84 assert!(nms.is_null());
86 // Pointers to unsized types -- trait objects
87 let ci: *const dyn ToString = &3;
88 assert!(!ci.is_null());
90 let mi: *mut dyn ToString = &mut 3;
91 assert!(!mi.is_null());
93 let nci: *const dyn ToString = null::<isize>();
94 assert!(nci.is_null());
96 let nmi: *mut dyn ToString = null_mut::<isize>();
97 assert!(nmi.is_null());
99 #[cfg(not(bootstrap))]
104 let ec: *const Extern = null::<Extern>();
105 assert!(ec.is_null());
107 let em: *mut Extern = null_mut::<Extern>();
108 assert!(em.is_null());
115 let p: *const isize = null();
116 assert_eq!(p.as_ref(), None);
118 let q: *const isize = &2;
119 assert_eq!(q.as_ref().unwrap(), &2);
121 let p: *mut isize = null_mut();
122 assert_eq!(p.as_ref(), None);
124 let q: *mut isize = &mut 2;
125 assert_eq!(q.as_ref().unwrap(), &2);
127 // Lifetime inference
130 let p = &u as *const isize;
131 assert_eq!(p.as_ref().unwrap(), &2);
134 // Pointers to unsized types -- slices
135 let s: &mut [u8] = &mut [1, 2, 3];
136 let cs: *const [u8] = s;
137 assert_eq!(cs.as_ref(), Some(&*s));
139 let ms: *mut [u8] = s;
140 assert_eq!(ms.as_ref(), Some(&*s));
142 let cz: *const [u8] = &[];
143 assert_eq!(cz.as_ref(), Some(&[][..]));
145 let mz: *mut [u8] = &mut [];
146 assert_eq!(mz.as_ref(), Some(&[][..]));
148 let ncs: *const [u8] = null::<[u8; 3]>();
149 assert_eq!(ncs.as_ref(), None);
151 let nms: *mut [u8] = null_mut::<[u8; 3]>();
152 assert_eq!(nms.as_ref(), None);
154 // Pointers to unsized types -- trait objects
155 let ci: *const dyn ToString = &3;
156 assert!(ci.as_ref().is_some());
158 let mi: *mut dyn ToString = &mut 3;
159 assert!(mi.as_ref().is_some());
161 let nci: *const dyn ToString = null::<isize>();
162 assert!(nci.as_ref().is_none());
164 let nmi: *mut dyn ToString = null_mut::<isize>();
165 assert!(nmi.as_ref().is_none());
172 let p: *mut isize = null_mut();
173 assert!(p.as_mut() == None);
175 let q: *mut isize = &mut 2;
176 assert!(q.as_mut().unwrap() == &mut 2);
178 // Lifetime inference
181 let p = &mut u as *mut isize;
182 assert!(p.as_mut().unwrap() == &mut 2);
185 // Pointers to unsized types -- slices
186 let s: &mut [u8] = &mut [1, 2, 3];
187 let ms: *mut [u8] = s;
188 assert_eq!(ms.as_mut(), Some(&mut [1, 2, 3][..]));
190 let mz: *mut [u8] = &mut [];
191 assert_eq!(mz.as_mut(), Some(&mut [][..]));
193 let nms: *mut [u8] = null_mut::<[u8; 3]>();
194 assert_eq!(nms.as_mut(), None);
196 // Pointers to unsized types -- trait objects
197 let mi: *mut dyn ToString = &mut 3;
198 assert!(mi.as_mut().is_some());
200 let nmi: *mut dyn ToString = null_mut::<isize>();
201 assert!(nmi.as_mut().is_none());
206 fn test_ptr_addition() {
208 let xs = vec![5; 16];
209 let mut ptr = xs.as_ptr();
210 let end = ptr.offset(16);
218 let mut m_ptr = xs_mut.as_mut_ptr();
219 let m_end = m_ptr.offset(16);
221 while m_ptr < m_end {
223 m_ptr = m_ptr.offset(1);
226 assert!(xs_mut == vec![10; 16]);
231 fn test_ptr_subtraction() {
233 let xs = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
235 let ptr = xs.as_ptr();
238 assert_eq!(*(ptr.offset(idx as isize)), idx as isize);
243 let m_start = xs_mut.as_mut_ptr();
244 let mut m_ptr = m_start.offset(9);
248 if m_ptr == m_start {
251 m_ptr = m_ptr.offset(-1);
254 assert_eq!(xs_mut, [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]);
259 fn test_set_memory() {
260 let mut xs = [0u8; 20];
261 let ptr = xs.as_mut_ptr();
263 write_bytes(ptr, 5u8, xs.len());
265 assert!(xs == [5u8; 20]);
269 fn test_set_memory_const() {
270 const XS: [u8; 20] = {
271 let mut xs = [0u8; 20];
272 let ptr = xs.as_mut_ptr();
274 ptr.write_bytes(5u8, xs.len());
279 assert!(XS == [5u8; 20]);
283 fn test_unsized_nonnull() {
284 let xs: &[i32] = &[1, 2, 3];
285 let ptr = unsafe { NonNull::new_unchecked(xs as *const [i32] as *mut [i32]) };
286 let ys = unsafe { ptr.as_ref() };
287 let zs: &[i32] = &[1, 2, 3];
292 fn test_const_nonnull_new() {
294 assert!(NonNull::new(core::ptr::null_mut::<()>()).is_none());
296 let value = &mut 0u32;
297 let mut ptr = NonNull::new(value).unwrap();
298 unsafe { *ptr.as_mut() = 42 };
300 let reference = unsafe { &*ptr.as_ref() };
301 assert!(*reference == *value);
302 assert!(*reference == 42);
307 #[cfg(unix)] // printf may not be available on other platforms
308 #[allow(deprecated)] // For SipHasher
309 pub fn test_variadic_fnptr() {
311 use core::hash::{Hash, SipHasher};
313 // This needs to use the correct function signature even though it isn't called as some
314 // codegen backends make it UB to declare a function with multiple conflicting signatures
315 // (like LLVM) while others straight up return an error (like Cranelift).
316 fn printf(_: *const ffi::c_char, ...) -> ffi::c_int;
318 let p: unsafe extern "C" fn(*const ffi::c_char, ...) -> ffi::c_int = printf;
322 let mut s = SipHasher::new();
323 assert_eq!(p.hash(&mut s), q.hash(&mut s));
327 fn write_unaligned_drop() {
329 static DROPS: RefCell<Vec<u32>> = RefCell::new(Vec::new());
334 impl Drop for Dropper {
336 DROPS.with(|d| d.borrow_mut().push(self.0));
342 let mut t = Dropper(1);
344 write_unaligned(&mut t, c);
347 DROPS.with(|d| assert_eq!(*d.borrow(), [0]));
351 fn align_offset_zst() {
352 // For pointers of stride = 0, the pointer is already aligned or it cannot be aligned at
353 // all, because no amount of elements will align the pointer.
356 assert_eq!((p as *const ()).align_offset(p), 0);
358 assert_eq!(((p + 1) as *const ()).align_offset(p), !0);
360 p = (p + 1).next_power_of_two();
365 fn align_offset_stride1() {
366 // For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
370 for ptr in 1..2 * align {
371 let expected = ptr % align;
372 let offset = if expected == 0 { 0 } else { align - expected };
374 (ptr as *const u8).align_offset(align),
376 "ptr = {}, align = {}, size = 1",
381 align = (align + 1).next_power_of_two();
386 fn align_offset_weird_strides() {
395 struct A7(u32, u16, u8);
399 struct A9(u32, u32, u8);
401 struct A10(u32, u32, u16);
403 unsafe fn test_weird_stride<T>(ptr: *const T, align: usize) -> bool {
404 let numptr = ptr as usize;
405 let mut expected = usize::MAX;
406 // Naive but definitely correct way to find the *first* aligned element of stride::<T>.
408 if (numptr + el * ::std::mem::size_of::<T>()) % align == 0 {
413 let got = ptr.align_offset(align);
416 "aligning {:p} (with stride of {}) to {}, expected {}, got {}",
418 ::std::mem::size_of::<T>(),
428 // For pointers of stride != 1, we verify the algorithm against the naivest possible
433 let limit = if cfg!(miri) { 32 } else { 1024 };
434 while align < limit {
435 for ptr in 1usize..4 * align {
437 x |= test_weird_stride::<A3>(ptr as *const A3, align);
438 x |= test_weird_stride::<A4>(ptr as *const A4, align);
439 x |= test_weird_stride::<A5>(ptr as *const A5, align);
440 x |= test_weird_stride::<A6>(ptr as *const A6, align);
441 x |= test_weird_stride::<A7>(ptr as *const A7, align);
442 x |= test_weird_stride::<A8>(ptr as *const A8, align);
443 x |= test_weird_stride::<A9>(ptr as *const A9, align);
444 x |= test_weird_stride::<A10>(ptr as *const A10, align);
447 align = (align + 1).next_power_of_two();
455 let ptr1: *mut i32 = &mut a[1];
456 let ptr2: *mut i32 = &mut a[3];
458 assert_eq!(ptr2.offset_from(ptr1), 2);
459 assert_eq!(ptr1.offset_from(ptr2), -2);
460 assert_eq!(ptr1.offset(2), ptr2);
461 assert_eq!(ptr2.offset(-2), ptr1);
468 struct Pair<A, B: ?Sized>(A, B);
472 let () = metadata(&());
473 let () = metadata(&Unit);
474 let () = metadata(&4_u32);
475 let () = metadata(&String::new());
476 let () = metadata(&Some(4_u32));
477 let () = metadata(&ptr_metadata);
478 let () = metadata(&|| {});
479 let () = metadata(&[4, 7]);
480 let () = metadata(&(4, String::new()));
481 let () = metadata(&Pair(4, String::new()));
482 let () = metadata(0 as *const Extern);
483 let () = metadata(0 as *const <&u32 as std::ops::Deref>::Target);
485 assert_eq!(metadata("foo"), 3_usize);
486 assert_eq!(metadata(&[4, 7][..]), 2_usize);
488 let dst_tuple: &(bool, [u8]) = &(true, [0x66, 0x6F, 0x6F]);
489 let dst_struct: &Pair<bool, [u8]> = &Pair(true, [0x66, 0x6F, 0x6F]);
490 assert_eq!(metadata(dst_tuple), 3_usize);
491 assert_eq!(metadata(dst_struct), 3_usize);
493 let dst_tuple: &(bool, str) = std::mem::transmute(dst_tuple);
494 let dst_struct: &Pair<bool, str> = std::mem::transmute(dst_struct);
495 assert_eq!(&dst_tuple.1, "foo");
496 assert_eq!(&dst_struct.1, "foo");
497 assert_eq!(metadata(dst_tuple), 3_usize);
498 assert_eq!(metadata(dst_struct), 3_usize);
501 let vtable_1: DynMetadata<dyn Debug> = metadata(&4_u16 as &dyn Debug);
502 let vtable_2: DynMetadata<dyn Display> = metadata(&4_u16 as &dyn Display);
503 let vtable_3: DynMetadata<dyn Display> = metadata(&4_u32 as &dyn Display);
504 let vtable_4: DynMetadata<dyn Display> = metadata(&(true, 7_u32) as &(bool, dyn Display));
505 let vtable_5: DynMetadata<dyn Display> =
506 metadata(&Pair(true, 7_u32) as &Pair<bool, dyn Display>);
508 let address_1: *const () = std::mem::transmute(vtable_1);
509 let address_2: *const () = std::mem::transmute(vtable_2);
510 let address_3: *const () = std::mem::transmute(vtable_3);
511 let address_4: *const () = std::mem::transmute(vtable_4);
512 let address_5: *const () = std::mem::transmute(vtable_5);
513 // Different trait => different vtable pointer
514 assert_ne!(address_1, address_2);
515 // Different erased type => different vtable pointer
516 assert_ne!(address_2, address_3);
517 // Same erased type and same trait => same vtable pointer
518 assert_eq!(address_3, address_4);
519 assert_eq!(address_3, address_5);
524 fn ptr_metadata_bounds() {
525 fn metadata_eq_method_address<T: ?Sized>() -> usize {
526 // The `Metadata` associated type has an `Ord` bound, so this is valid:
527 <<T as Pointee>::Metadata as PartialEq>::eq as usize
529 // "Synthetic" trait impls generated by the compiler like those of `Pointee`
530 // are not checked for bounds of associated type.
531 // So with a buggy libcore we could have both:
532 // * `<dyn Display as Pointee>::Metadata == DynMetadata`
533 // * `DynMetadata: !PartialEq`
534 // … and cause an ICE here:
535 metadata_eq_method_address::<dyn Display>();
537 // For this reason, let’s check here that bounds are satisfied:
539 let _ = static_assert_expected_bounds_for_metadata::<()>;
540 let _ = static_assert_expected_bounds_for_metadata::<usize>;
541 let _ = static_assert_expected_bounds_for_metadata::<DynMetadata<dyn Display>>;
542 fn _static_assert_associated_type<T: ?Sized>() {
543 let _ = static_assert_expected_bounds_for_metadata::<<T as Pointee>::Metadata>;
546 fn static_assert_expected_bounds_for_metadata<Meta>()
548 // Keep this in sync with the associated type in `library/core/src/ptr/metadata.rs`
549 Meta: Copy + Send + Sync + Ord + std::hash::Hash + Unpin,
558 struct Something([u8; 47]);
560 let value = Something([0; 47]);
561 let trait_object: &dyn Debug = &value;
562 let meta = metadata(trait_object);
564 assert_eq!(meta.size_of(), 64);
565 assert_eq!(meta.size_of(), std::mem::size_of::<Something>());
566 assert_eq!(meta.align_of(), 32);
567 assert_eq!(meta.align_of(), std::mem::align_of::<Something>());
568 assert_eq!(meta.layout(), std::alloc::Layout::new::<Something>());
570 assert!(format!("{meta:?}").starts_with("DynMetadata(0x"));
574 fn from_raw_parts() {
575 let mut value = 5_u32;
576 let address = &mut value as *mut _ as *mut ();
577 let trait_object: &dyn Display = &mut value;
578 let vtable = metadata(trait_object);
579 let trait_object = NonNull::from(trait_object);
581 assert_eq!(ptr::from_raw_parts(address, vtable), trait_object.as_ptr());
582 assert_eq!(ptr::from_raw_parts_mut(address, vtable), trait_object.as_ptr());
583 assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), vtable), trait_object);
585 let mut array = [5_u32, 5, 5, 5, 5];
586 let address = &mut array as *mut _ as *mut ();
587 let array_ptr = NonNull::from(&mut array);
588 let slice_ptr = NonNull::from(&mut array[..]);
590 assert_eq!(ptr::from_raw_parts(address, ()), array_ptr.as_ptr());
591 assert_eq!(ptr::from_raw_parts_mut(address, ()), array_ptr.as_ptr());
592 assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), ()), array_ptr);
594 assert_eq!(ptr::from_raw_parts(address, 5), slice_ptr.as_ptr());
595 assert_eq!(ptr::from_raw_parts_mut(address, 5), slice_ptr.as_ptr());
596 assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), 5), slice_ptr);
601 let foo = ThinBox::<dyn Display>::new(4);
602 assert_eq!(foo.to_string(), "4");
604 let bar = ThinBox::<dyn Display>::new(7);
605 assert_eq!(bar.to_string(), "7");
607 // A slightly more interesting library that could be built on top of metadata APIs.
609 // * It could be generalized to any `T: ?Sized` (not just trait object)
610 // if `{size,align}_of_for_meta<T: ?Sized>(T::Metadata)` are added.
611 // * Constructing a `ThinBox` without consuming and deallocating a `Box`
612 // requires either the unstable `Unsize` marker trait,
613 // or the unstable `unsized_locals` language feature,
614 // or taking `&dyn T` and restricting to `T: Copy`.
617 use std::marker::PhantomData;
621 T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
623 ptr: NonNull<DynMetadata<T>>,
624 phantom: PhantomData<T>,
629 T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
631 pub fn new<Value: std::marker::Unsize<T>>(value: Value) -> Self {
632 let unsized_: &T = &value;
633 let meta = metadata(unsized_);
634 let meta_layout = Layout::for_value(&meta);
635 let value_layout = Layout::for_value(&value);
636 let (layout, offset) = meta_layout.extend(value_layout).unwrap();
637 // `DynMetadata` is pointer-sized:
638 assert!(layout.size() > 0);
639 // If `ThinBox<T>` is generalized to any `T: ?Sized`,
640 // handle ZSTs with a dangling pointer without going through `alloc()`,
641 // like `Box<T>` does.
643 let ptr = NonNull::new(alloc(layout))
644 .unwrap_or_else(|| handle_alloc_error(layout))
645 .cast::<DynMetadata<T>>();
646 ptr.as_ptr().write(meta);
647 ptr.cast::<u8>().as_ptr().add(offset).cast::<Value>().write(value);
648 Self { ptr, phantom: PhantomData }
652 fn meta(&self) -> DynMetadata<T> {
653 unsafe { *self.ptr.as_ref() }
656 fn layout(&self) -> (Layout, usize) {
657 let meta = self.meta();
658 Layout::for_value(&meta).extend(meta.layout()).unwrap()
661 fn value_ptr(&self) -> *const T {
662 let (_, offset) = self.layout();
663 let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
664 ptr::from_raw_parts(data_ptr.cast(), self.meta())
667 fn value_mut_ptr(&mut self) -> *mut T {
668 let (_, offset) = self.layout();
669 // FIXME: can this line be shared with the same in `value_ptr()`
670 // without upsetting Stacked Borrows?
671 let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
672 from_raw_parts_mut(data_ptr.cast(), self.meta())
676 impl<T> std::ops::Deref for ThinBox<T>
678 T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
682 fn deref(&self) -> &T {
683 unsafe { &*self.value_ptr() }
687 impl<T> std::ops::DerefMut for ThinBox<T>
689 T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
691 fn deref_mut(&mut self) -> &mut T {
692 unsafe { &mut *self.value_mut_ptr() }
696 impl<T> std::ops::Drop for ThinBox<T>
698 T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
701 let (layout, _) = self.layout();
703 drop_in_place::<T>(&mut **self);
704 dealloc(self.ptr.cast().as_ptr(), layout);
711 fn nonnull_tagged_pointer_with_provenance() {
712 let raw_pointer = Box::into_raw(Box::new(10));
714 let mut p = TaggedPointer::new(raw_pointer).unwrap();
715 assert_eq!(p.tag(), 0);
718 assert_eq!(p.tag(), 1);
719 assert_eq!(unsafe { *p.pointer().as_ptr() }, 10);
722 assert_eq!(p.tag(), 3);
723 assert_eq!(unsafe { *p.pointer().as_ptr() }, 10);
725 unsafe { Box::from_raw(p.pointer().as_ptr()) };
727 /// A non-null pointer type which carries several bits of metadata and maintains provenance.
729 pub struct TaggedPointer<T>(NonNull<T>);
731 impl<T> Clone for TaggedPointer<T> {
732 fn clone(&self) -> Self {
737 impl<T> Copy for TaggedPointer<T> {}
739 impl<T> TaggedPointer<T> {
740 /// The ABI-required minimum alignment of the `P` type.
741 pub const ALIGNMENT: usize = core::mem::align_of::<T>();
742 /// A mask for data-carrying bits of the address.
743 pub const DATA_MASK: usize = !Self::ADDRESS_MASK;
744 /// Number of available bits of storage in the address.
745 pub const NUM_BITS: u32 = Self::ALIGNMENT.trailing_zeros();
746 /// A mask for the non-data-carrying bits of the address.
747 pub const ADDRESS_MASK: usize = usize::MAX << Self::NUM_BITS;
749 /// Create a new tagged pointer from a possibly null pointer.
750 pub fn new(pointer: *mut T) -> Option<TaggedPointer<T>> {
751 Some(TaggedPointer(NonNull::new(pointer)?))
754 /// Consume this tagged pointer and produce a raw mutable pointer to the
756 pub fn pointer(self) -> NonNull<T> {
757 // SAFETY: The `addr` guaranteed to have bits set in the Self::ADDRESS_MASK, so the result will be non-null.
758 self.0.map_addr(|addr| unsafe {
759 NonZeroUsize::new_unchecked(addr.get() & Self::ADDRESS_MASK)
763 /// Consume this tagged pointer and produce the data it carries.
764 pub fn tag(&self) -> usize {
765 self.0.addr().get() & Self::DATA_MASK
768 /// Update the data this tagged pointer carries to a new value.
769 pub fn set_tag(&mut self, data: usize) {
771 data & Self::ADDRESS_MASK,
773 "cannot set more data beyond the lowest NUM_BITS"
775 let data = data & Self::DATA_MASK;
777 // SAFETY: This value will always be non-zero because the upper bits (from
778 // ADDRESS_MASK) will always be non-zero. This a property of the type and its
780 self.0 = self.0.map_addr(|addr| unsafe {
781 NonZeroUsize::new_unchecked((addr.get() & Self::ADDRESS_MASK) | data)
788 fn test_const_copy() {
793 // Copy ptr1 to ptr2, bytewise.
796 &ptr1 as *const _ as *const MaybeUninit<u8>,
797 &mut ptr2 as *mut _ as *mut MaybeUninit<u8>,
798 mem::size_of::<&i32>(),
802 // Make sure they still work.
811 // Copy ptr1 to ptr2, bytewise.
813 ptr::copy_nonoverlapping(
814 &ptr1 as *const _ as *const MaybeUninit<u8>,
815 &mut ptr2 as *mut _ as *mut MaybeUninit<u8>,
816 mem::size_of::<&i32>(),
820 // Make sure they still work.