Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2054 insertions, 0 deletions

diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
new file mode 100644
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+//! Manually manage memory through raw pointers.
+//!
+//! *[See also the pointer primitive types](pointer).*
+//!
+//! # Safety
+//!
+//! Many functions in this module take raw pointers as arguments and read from
+//! or write to them. For this to be safe, these pointers must be *valid*.
+//! Whether a pointer is valid depends on the operation it is used for
+//! (read or write), and the extent of the memory that is accessed (i.e.,
+//! how many bytes are read/written). Most functions use `*mut T` and `*const T`
+//! to access only a single value, in which case the documentation omits the size
+//! and implicitly assumes it to be `size_of::<T>()` bytes.
+//!
+//! The precise rules for validity are not determined yet. The guarantees that are
+//! provided at this point are very minimal:
+//!
+//! * A [null] pointer is *never* valid, not even for accesses of [size zero][zst].
+//! * For a pointer to be valid, it is necessary, but not always sufficient, that the pointer
+//!   be *dereferenceable*: the memory range of the given size starting at the pointer must all be
+//!   within the bounds of a single allocated object. Note that in Rust,
+//!   every (stack-allocated) variable is considered a separate allocated object.
+//! * Even for operations of [size zero][zst], the pointer must not be pointing to deallocated
+//!   memory, i.e., deallocation makes pointers invalid even for zero-sized operations. However,
+//!   casting any non-zero integer *literal* to a pointer is valid for zero-sized accesses, even if
+//!   some memory happens to exist at that address and gets deallocated. This corresponds to writing
+//!   your own allocator: allocating zero-sized objects is not very hard. The canonical way to
+//!   obtain a pointer that is valid for zero-sized accesses is [`NonNull::dangling`].
+//FIXME: mention `ptr::invalid` above, once it is stable.
+//! * All accesses performed by functions in this module are *non-atomic* in the sense
+//!   of [atomic operations] used to synchronize between threads. This means it is
+//!   undefined behavior to perform two concurrent accesses to the same location from different
+//!   threads unless both accesses only read from memory. Notice that this explicitly
+//!   includes [`read_volatile`] and [`write_volatile`]: Volatile accesses cannot
+//!   be used for inter-thread synchronization.
+//! * The result of casting a reference to a pointer is valid for as long as the
+//!   underlying object is live and no reference (just raw pointers) is used to
+//!   access the same memory.
+//!
+//! These axioms, along with careful use of [`offset`] for pointer arithmetic,
+//! are enough to correctly implement many useful things in unsafe code. Stronger guarantees
+//! will be provided eventually, as the [aliasing] rules are being determined. For more
+//! information, see the [book] as well as the section in the reference devoted
+//! to [undefined behavior][ub].
+//!
+//! ## Alignment
+//!
+//! Valid raw pointers as defined above are not necessarily properly aligned (where
+//! "proper" alignment is defined by the pointee type, i.e., `*const T` must be
+//! aligned to `mem::align_of::<T>()`). However, most functions require their
+//! arguments to be properly aligned, and will explicitly state
+//! this requirement in their documentation. Notable exceptions to this are
+//! [`read_unaligned`] and [`write_unaligned`].
+//!
+//! When a function requires proper alignment, it does so even if the access
+//! has size 0, i.e., even if memory is not actually touched. Consider using
+//! [`NonNull::dangling`] in such cases.
+//!
+//! ## Allocated object
+//!
+//! For several operations, such as [`offset`] or field projections (`expr.field`), the notion of an
+//! "allocated object" becomes relevant. An allocated object is a contiguous region of memory.
+//! Common examples of allocated objects include stack-allocated variables (each variable is a
+//! separate allocated object), heap allocations (each allocation created by the global allocator is
+//! a separate allocated object), and `static` variables.
+//!
+//!
+//! # Strict Provenance
+//!
+//! **The following text is non-normative, insufficiently formal, and is an extremely strict
+//! interpretation of provenance. It's ok if your code doesn't strictly conform to it.**
+//!
+//! [Strict Provenance][] is an experimental set of APIs that help tools that try
+//! to validate the memory-safety of your program's execution. Notably this includes [Miri][]
+//! and [CHERI][], which can detect when you access out of bounds memory or otherwise violate
+//! Rust's memory model.
+//!
+//! Provenance must exist in some form for any programming
+//! language compiled for modern computer architectures, but specifying a model for provenance
+//! in a way that is useful to both compilers and programmers is an ongoing challenge.
+//! The [Strict Provenance][] experiment seeks to explore the question: *what if we just said you
+//! couldn't do all the nasty operations that make provenance so messy?*
+//!
+//! What APIs would have to be removed? What APIs would have to be added? How much would code
+//! have to change, and is it worse or better now? Would any patterns become truly inexpressible?
+//! Could we carve out special exceptions for those patterns? Should we?
+//!
+//! A secondary goal of this project is to see if we can disambiguate the many functions of
+//! pointer<->integer casts enough for the definition of `usize` to be loosened so that it
+//! isn't *pointer*-sized but address-space/offset/allocation-sized (we'll probably continue
+//! to conflate these notions). This would potentially make it possible to more efficiently
+//! target platforms where pointers are larger than offsets, such as CHERI and maybe some
+//! segmented architecures.
+//!
+//! ## Provenance
+//!
+//! **This section is *non-normative* and is part of the [Strict Provenance][] experiment.**
+//!
+//! Pointers are not *simply* an "integer" or "address". For instance, it's uncontroversial
+//! to say that a Use After Free is clearly Undefined Behaviour, even if you "get lucky"
+//! and the freed memory gets reallocated before your read/write (in fact this is the
+//! worst-case scenario, UAFs would be much less concerning if this didn't happen!).
+//! To rationalize this claim, pointers need to somehow be *more* than just their addresses:
+//! they must have provenance.
+//!
+//! When an allocation is created, that allocation has a unique Original Pointer. For alloc
+//! APIs this is literally the pointer the call returns, and for local variables and statics,
+//! this is the name of the variable/static. This is mildly overloading the term "pointer"
+//! for the sake of brevity/exposition.
+//!
+//! The Original Pointer for an allocation is guaranteed to have unique access to the entire
+//! allocation and *only* that allocation. In this sense, an allocation can be thought of
+//! as a "sandbox" that cannot be broken into or out of. *Provenance* is the permission
+//! to access an allocation's sandbox and has both a *spatial* and *temporal* component:
+//!
+//! * Spatial: A range of bytes that the pointer is allowed to access.
+//! * Temporal: The lifetime (of the allocation) that access to these bytes is tied to.
+//!
+//! Spatial provenance makes sure you don't go beyond your sandbox, while temporal provenance
+//! makes sure that you can't "get lucky" after your permission to access some memory
+//! has been revoked (either through deallocations or borrows expiring).
+//!
+//! Provenance is implicitly shared with all pointers transitively derived from
+//! The Original Pointer through operations like [`offset`], borrowing, and pointer casts.
+//! Some operations may *shrink* the derived provenance, limiting how much memory it can
+//! access or how long it's valid for (i.e. borrowing a subfield and subslicing).
+//!
+//! Shrinking provenance cannot be undone: even if you "know" there is a larger allocation, you
+//! can't derive a pointer with a larger provenance. Similarly, you cannot "recombine"
+//! two contiguous provenances back into one (i.e. with a `fn merge(&[T], &[T]) -> &[T]`).
+//!
+//! A reference to a value always has provenance over exactly the memory that field occupies.
+//! A reference to a slice always has provenance over exactly the range that slice describes.
+//!
+//! If an allocation is deallocated, all pointers with provenance to that allocation become
+//! invalidated, and effectively lose their provenance.
+//!
+//! The strict provenance experiment is mostly only interested in exploring stricter *spatial*
+//! provenance. In this sense it can be thought of as a subset of the more ambitious and
+//! formal [Stacked Borrows][] research project, which is what tools like [Miri][] are based on.
+//! In particular, Stacked Borrows is necessary to properly describe what borrows are allowed
+//! to do and when they become invalidated. This necessarily involves much more complex
+//! *temporal* reasoning than simply identifying allocations. Adjusting APIs and code
+//! for the strict provenance experiment will also greatly help Stacked Borrows.
+//!
+//!
+//! ## Pointer Vs Addresses
+//!
+//! **This section is *non-normative* and is part of the [Strict Provenance][] experiment.**
+//!
+//! One of the largest historical issues with trying to define provenance is that programmers
+//! freely convert between pointers and integers. Once you allow for this, it generally becomes
+//! impossible to accurately track and preserve provenance information, and you need to appeal
+//! to very complex and unreliable heuristics. But of course, converting between pointers and
+//! integers is very useful, so what can we do?
+//!
+//! Also did you know WASM is actually a "Harvard Architecture"? As in function pointers are
+//! handled completely differently from data pointers? And we kind of just shipped Rust on WASM
+//! without really addressing the fact that we let you freely convert between function pointers
+//! and data pointers, because it mostly Just Works? Let's just put that on the "pointer casts
+//! are dubious" pile.
+//!
+//! Strict Provenance attempts to square these circles by decoupling Rust's traditional conflation
+//! of pointers and `usize` (and `isize`), and defining a pointer to semantically contain the
+//! following information:
+//!
+//! * The **address-space** it is part of (e.g. "data" vs "code" in WASM).
+//! * The **address** it points to, which can be represented by a `usize`.
+//! * The **provenance** it has, defining the memory it has permission to access.
+//!
+//! Under Strict Provenance, a usize *cannot* accurately represent a pointer, and converting from
+//! a pointer to a usize is generally an operation which *only* extracts the address. It is
+//! therefore *impossible* to construct a valid pointer from a usize because there is no way
+//! to restore the address-space and provenance. In other words, pointer-integer-pointer
+//! roundtrips are not possible (in the sense that the resulting pointer is not dereferencable).
+//!
+//! The key insight to making this model *at all* viable is the [`with_addr`][] method:
+//!
+//! ```text
+//!     /// Creates a new pointer with the given address.
+//!     ///
+//!     /// This performs the same operation as an `addr as ptr` cast, but copies
+//!     /// the *address-space* and *provenance* of `self` to the new pointer.
+//!     /// This allows us to dynamically preserve and propagate this important
+//!     /// information in a way that is otherwise impossible with a unary cast.
+//!     ///
+//!     /// This is equivalent to using `wrapping_offset` to offset `self` to the
+//!     /// given address, and therefore has all the same capabilities and restrictions.
+//!     pub fn with_addr(self, addr: usize) -> Self;
+//! ```
+//!
+//! So you're still able to drop down to the address representation and do whatever
+//! clever bit tricks you want *as long as* you're able to keep around a pointer
+//! into the allocation you care about that can "reconstitute" the other parts of the pointer.
+//! Usually this is very easy, because you only are taking a pointer, messing with the address,
+//! and then immediately converting back to a pointer. To make this use case more ergonomic,
+//! we provide the [`map_addr`][] method.
+//!
+//! To help make it clear that code is "following" Strict Provenance semantics, we also provide an
+//! [`addr`][] method which promises that the returned address is not part of a
+//! pointer-usize-pointer roundtrip. In the future we may provide a lint for pointer<->integer
+//! casts to help you audit if your code conforms to strict provenance.
+//!
+//!
+//! ## Using Strict Provenance
+//!
+//! Most code needs no changes to conform to strict provenance, as the only really concerning
+//! operation that *wasn't* obviously already Undefined Behaviour is casts from usize to a
+//! pointer. For code which *does* cast a usize to a pointer, the scope of the change depends
+//! on exactly what you're doing.
+//!
+//! In general you just need to make sure that if you want to convert a usize address to a
+//! pointer and then use that pointer to read/write memory, you need to keep around a pointer
+//! that has sufficient provenance to perform that read/write itself. In this way all of your
+//! casts from an address to a pointer are essentially just applying offsets/indexing.
+//!
+//! This is generally trivial to do for simple cases like tagged pointers *as long as you
+//! represent the tagged pointer as an actual pointer and not a usize*. For instance:
+//!
+//! ```
+//! #![feature(strict_provenance)]
+//!
+//! unsafe {
+//!     // A flag we want to pack into our pointer
+//!     static HAS_DATA: usize = 0x1;
+//!     static FLAG_MASK: usize = !HAS_DATA;
+//!
+//!     // Our value, which must have enough alignment to have spare least-significant-bits.
+//!     let my_precious_data: u32 = 17;
+//!     assert!(core::mem::align_of::<u32>() > 1);
+//!
+//!     // Create a tagged pointer
+//!     let ptr = &my_precious_data as *const u32;
+//!     let tagged = ptr.map_addr(|addr| addr | HAS_DATA);
+//!
+//!     // Check the flag:
+//!     if tagged.addr() & HAS_DATA != 0 {
+//!         // Untag and read the pointer
+//!         let data = *tagged.map_addr(|addr| addr & FLAG_MASK);
+//!         assert_eq!(data, 17);
+//!     } else {
+//!         unreachable!()
+//!     }
+//! }
+//! ```
+//!
+//! (Yes, if you've been using AtomicUsize for pointers in concurrent datastructures, you should
+//! be using AtomicPtr instead. If that messes up the way you atomically manipulate pointers,
+//! we would like to know why, and what needs to be done to fix it.)
+//!
+//! Something more complicated and just generally *evil* like an XOR-List requires more significant
+//! changes like allocating all nodes in a pre-allocated Vec or Arena and using a pointer
+//! to the whole allocation to reconstitute the XORed addresses.
+//!
+//! Situations where a valid pointer *must* be created from just an address, such as baremetal code
+//! accessing a memory-mapped interface at a fixed address, are an open question on how to support.
+//! These situations *will* still be allowed, but we might require some kind of "I know what I'm
+//! doing" annotation to explain the situation to the compiler. It's also possible they need no
+//! special attention at all, because they're generally accessing memory outside the scope of
+//! "the abstract machine", or already using "I know what I'm doing" annotations like "volatile".
+//!
+//! Under [Strict Provenance] it is Undefined Behaviour to:
+//!
+//! * Access memory through a pointer that does not have provenance over that memory.
+//!
+//! * [`offset`] a pointer to or from an address it doesn't have provenance over.
+//!   This means it's always UB to offset a pointer derived from something deallocated,
+//!   even if the offset is 0. Note that a pointer "one past the end" of its provenance
+//!   is not actually outside its provenance, it just has 0 bytes it can load/store.
+//!
+//! But it *is* still sound to:
+//!
+//! * Create an invalid pointer from just an address (see [`ptr::invalid`][]). This can
+//!   be used for sentinel values like `null` *or* to represent a tagged pointer that will
+//!   never be dereferencable. In general, it is always sound for an integer to pretend
+//!   to be a pointer "for fun" as long as you don't use operations on it which require
+//!   it to be valid (offset, read, write, etc).
+//!
+//! * Forge an allocation of size zero at any sufficiently aligned non-null address.
+//!   i.e. the usual "ZSTs are fake, do what you want" rules apply *but* this only applies
+//!   for actual forgery (integers cast to pointers). If you borrow some struct's field
+//!   that *happens* to be zero-sized, the resulting pointer will have provenance tied to
+//!   that allocation and it will still get invalidated if the allocation gets deallocated.
+//!   In the future we may introduce an API to make such a forged allocation explicit.
+//!
+//! * [`wrapping_offset`][] a pointer outside its provenance. This includes invalid pointers
+//!   which have "no" provenance. Unfortunately there may be practical limits on this for a
+//!   particular platform, and it's an open question as to how to specify this (if at all).
+//!   Notably, [CHERI][] relies on a compression scheme that can't handle a
+//!   pointer getting offset "too far" out of bounds. If this happens, the address
+//!   returned by `addr` will be the value you expect, but the provenance will get invalidated
+//!   and using it to read/write will fault. The details of this are architecture-specific
+//!   and based on alignment, but the buffer on either side of the pointer's range is pretty
+//!   generous (think kilobytes, not bytes).
+//!
+//! * Compare arbitrary pointers by address. Addresses *are* just integers and so there is
+//!   always a coherent answer, even if the pointers are invalid or from different
+//!   address-spaces/provenances. Of course, comparing addresses from different address-spaces
+//!   is generally going to be *meaningless*, but so is comparing Kilograms to Meters, and Rust
+//!   doesn't prevent that either. Similarly, if you get "lucky" and notice that a pointer
+//!   one-past-the-end is the "same" address as the start of an unrelated allocation, anything
+//!   you do with that fact is *probably* going to be gibberish. The scope of that gibberish
+//!   is kept under control by the fact that the two pointers *still* aren't allowed to access
+//!   the other's allocation (bytes), because they still have different provenance.
+//!
+//! * Perform pointer tagging tricks. This falls out of [`wrapping_offset`] but is worth
+//!   mentioning in more detail because of the limitations of [CHERI][]. Low-bit tagging
+//!   is very robust, and often doesn't even go out of bounds because types ensure
+//!   size >= align (and over-aligning actually gives CHERI more flexibility). Anything
+//!   more complex than this rapidly enters "extremely platform-specific" territory as
+//!   certain things may or may not be allowed based on specific supported operations.
+//!   For instance, ARM explicitly supports high-bit tagging, and so CHERI on ARM inherits
+//!   that and should support it.
+//!
+//! ## Pointer-usize-pointer roundtrips and 'exposed' provenance
+//!
+//! **This section is *non-normative* and is part of the [Strict Provenance] experiment.**
+//!
+//! As discussed above, pointer-usize-pointer roundtrips are not possible under [Strict Provenance].
+//! However, there exists legacy Rust code that is full of such roundtrips, and legacy platform APIs
+//! regularly assume that `usize` can capture all the information that makes up a pointer. There
+//! also might be code that cannot be ported to Strict Provenance (which is something we would [like
+//! to hear about][Strict Provenance]).
+//!
+//! For situations like this, there is a fallback plan, a way to 'opt out' of Strict Provenance.
+//! However, note that this makes your code a lot harder to specify, and the code will not work
+//! (well) with tools like [Miri] and [CHERI].
+//!
+//! This fallback plan is provided by the [`expose_addr`] and [`from_exposed_addr`] methods (which
+//! are equivalent to `as` casts between pointers and integers). [`expose_addr`] is a lot like
+//! [`addr`], but additionally adds the provenance of the pointer to a global list of 'exposed'
+//! provenances. (This list is purely conceptual, it exists for the purpose of specifying Rust but
+//! is not materialized in actual executions, except in tools like [Miri].) [`from_exposed_addr`]
+//! can be used to construct a pointer with one of these previously 'exposed' provenances.
+//! [`from_exposed_addr`] takes only `addr: usize` as arguments, so unlike in [`with_addr`] there is
+//! no indication of what the correct provenance for the returned pointer is -- and that is exactly
+//! what makes pointer-usize-pointer roundtrips so tricky to rigorously specify! There is no
+//! algorithm that decides which provenance will be used. You can think of this as "guessing" the
+//! right provenance, and the guess will be "maximally in your favor", in the sense that if there is
+//! any way to avoid undefined behavior, then that is the guess that will be taken. However, if
+//! there is *no* previously 'exposed' provenance that justifies the way the returned pointer will
+//! be used, the program has undefined behavior.
+//!
+//! Using [`expose_addr`] or [`from_exposed_addr`] (or the equivalent `as` casts) means that code is
+//! *not* following Strict Provenance rules. The goal of the Strict Provenance experiment is to
+//! determine whether it is possible to use Rust without [`expose_addr`] and [`from_exposed_addr`].
+//! If this is successful, it would be a major win for avoiding specification complexity and to
+//! facilitate adoption of tools like [CHERI] and [Miri] that can be a big help in increasing the
+//! confidence in (unsafe) Rust code.
+//!
+//! [aliasing]: ../../nomicon/aliasing.html
+//! [book]: ../../book/ch19-01-unsafe-rust.html#dereferencing-a-raw-pointer
+//! [ub]: ../../reference/behavior-considered-undefined.html
+//! [zst]: ../../nomicon/exotic-sizes.html#zero-sized-types-zsts
+//! [atomic operations]: crate::sync::atomic
+//! [`offset`]: pointer::offset
+//! [`wrapping_offset`]: pointer::wrapping_offset
+//! [`with_addr`]: pointer::with_addr
+//! [`map_addr`]: pointer::map_addr
+//! [`addr`]: pointer::addr
+//! [`ptr::invalid`]: core::ptr::invalid
+//! [`expose_addr`]: pointer::expose_addr
+//! [`from_exposed_addr`]: from_exposed_addr
+//! [Miri]: https://github.com/rust-lang/miri
+//! [CHERI]: https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/
+//! [Strict Provenance]: https://github.com/rust-lang/rust/issues/95228
+//! [Stacked Borrows]: https://plv.mpi-sws.org/rustbelt/stacked-borrows/
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use crate::cmp::Ordering;
+use crate::fmt;
+use crate::hash;
+use crate::intrinsics::{
+    self, assert_unsafe_precondition, is_aligned_and_not_null, is_nonoverlapping,
+};
+
+use crate::mem::{self, MaybeUninit};
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(inline)]
+pub use crate::intrinsics::copy_nonoverlapping;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(inline)]
+pub use crate::intrinsics::copy;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[doc(inline)]
+pub use crate::intrinsics::write_bytes;
+
+mod metadata;
+pub(crate) use metadata::PtrRepr;
+#[unstable(feature = "ptr_metadata", issue = "81513")]
+pub use metadata::{from_raw_parts, from_raw_parts_mut, metadata, DynMetadata, Pointee, Thin};
+
+mod non_null;
+#[stable(feature = "nonnull", since = "1.25.0")]
+pub use non_null::NonNull;
+
+mod unique;
+#[unstable(feature = "ptr_internals", issue = "none")]
+pub use unique::Unique;
+
+mod const_ptr;
+mod mut_ptr;
+
+/// Executes the destructor (if any) of the pointed-to value.
+///
+/// This is semantically equivalent to calling [`ptr::read`] and discarding
+/// the result, but has the following advantages:
+///
+/// * It is *required* to use `drop_in_place` to drop unsized types like
+///   trait objects, because they can't be read out onto the stack and
+///   dropped normally.
+///
+/// * It is friendlier to the optimizer to do this over [`ptr::read`] when
+///   dropping manually allocated memory (e.g., in the implementations of
+///   `Box`/`Rc`/`Vec`), as the compiler doesn't need to prove that it's
+///   sound to elide the copy.
+///
+/// * It can be used to drop [pinned] data when `T` is not `repr(packed)`
+///   (pinned data must not be moved before it is dropped).
+///
+/// Unaligned values cannot be dropped in place, they must be copied to an aligned
+/// location first using [`ptr::read_unaligned`]. For packed structs, this move is
+/// done automatically by the compiler. This means the fields of packed structs
+/// are not dropped in-place.
+///
+/// [`ptr::read`]: self::read
+/// [`ptr::read_unaligned`]: self::read_unaligned
+/// [pinned]: crate::pin
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `to_drop` must be [valid] for both reads and writes.
+///
+/// * `to_drop` must be properly aligned.
+///
+/// * The value `to_drop` points to must be valid for dropping, which may mean it must uphold
+///   additional invariants - this is type-dependent.
+///
+/// Additionally, if `T` is not [`Copy`], using the pointed-to value after
+/// calling `drop_in_place` can cause undefined behavior. Note that `*to_drop =
+/// foo` counts as a use because it will cause the value to be dropped
+/// again. [`write()`] can be used to overwrite data without causing it to be
+/// dropped.
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null and properly aligned.
+///
+/// [valid]: self#safety
+///
+/// # Examples
+///
+/// Manually remove the last item from a vector:
+///
+/// ```
+/// use std::ptr;
+/// use std::rc::Rc;
+///
+/// let last = Rc::new(1);
+/// let weak = Rc::downgrade(&last);
+///
+/// let mut v = vec![Rc::new(0), last];
+///
+/// unsafe {
+///     // Get a raw pointer to the last element in `v`.
+///     let ptr = &mut v[1] as *mut _;
+///     // Shorten `v` to prevent the last item from being dropped. We do that first,
+///     // to prevent issues if the `drop_in_place` below panics.
+///     v.set_len(1);
+///     // Without a call `drop_in_place`, the last item would never be dropped,
+///     // and the memory it manages would be leaked.
+///     ptr::drop_in_place(ptr);
+/// }
+///
+/// assert_eq!(v, &[0.into()]);
+///
+/// // Ensure that the last item was dropped.
+/// assert!(weak.upgrade().is_none());
+/// ```
+#[stable(feature = "drop_in_place", since = "1.8.0")]
+#[lang = "drop_in_place"]
+#[allow(unconditional_recursion)]
+pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
+    // Code here does not matter - this is replaced by the
+    // real drop glue by the compiler.
+
+    // SAFETY: see comment above
+    unsafe { drop_in_place(to_drop) }
+}
+
+/// Creates a null raw pointer.
+///
+/// # Examples
+///
+/// ```
+/// use std::ptr;
+///
+/// let p: *const i32 = ptr::null();
+/// assert!(p.is_null());
+/// ```
+#[inline(always)]
+#[must_use]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_promotable]
+#[rustc_const_stable(feature = "const_ptr_null", since = "1.24.0")]
+#[rustc_allow_const_fn_unstable(ptr_metadata)]
+#[rustc_diagnostic_item = "ptr_null"]
+pub const fn null<T: ?Sized + Thin>() -> *const T {
+    from_raw_parts(invalid(0), ())
+}
+
+/// Creates an invalid pointer with the given address.
+///
+/// This is different from `addr as *const T`, which creates a pointer that picks up a previously
+/// exposed provenance. See [`from_exposed_addr`] for more details on that operation.
+///
+/// The module's top-level documentation discusses the precise meaning of an "invalid"
+/// pointer but essentially this expresses that the pointer is not associated
+/// with any actual allocation and is little more than a usize address in disguise.
+///
+/// This pointer will have no provenance associated with it and is therefore
+/// UB to read/write/offset. This mostly exists to facilitate things
+/// like `ptr::null` and `NonNull::dangling` which make invalid pointers.
+///
+/// (Standard "Zero-Sized-Types get to cheat and lie" caveats apply, although it
+/// may be desirable to give them their own API just to make that 100% clear.)
+///
+/// This API and its claimed semantics are part of the Strict Provenance experiment,
+/// see the [module documentation][crate::ptr] for details.
+#[inline(always)]
+#[must_use]
+#[rustc_const_stable(feature = "stable_things_using_strict_provenance", since = "1.61.0")]
+#[unstable(feature = "strict_provenance", issue = "95228")]
+pub const fn invalid<T>(addr: usize) -> *const T {
+    // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
+    // We use transmute rather than a cast so tools like Miri can tell that this
+    // is *not* the same as from_exposed_addr.
+    // SAFETY: every valid integer is also a valid pointer (as long as you don't dereference that
+    // pointer).
+    unsafe { mem::transmute(addr) }
+}
+
+/// Creates an invalid mutable pointer with the given address.
+///
+/// This is different from `addr as *mut T`, which creates a pointer that picks up a previously
+/// exposed provenance. See [`from_exposed_addr_mut`] for more details on that operation.
+///
+/// The module's top-level documentation discusses the precise meaning of an "invalid"
+/// pointer but essentially this expresses that the pointer is not associated
+/// with any actual allocation and is little more than a usize address in disguise.
+///
+/// This pointer will have no provenance associated with it and is therefore
+/// UB to read/write/offset. This mostly exists to facilitate things
+/// like `ptr::null` and `NonNull::dangling` which make invalid pointers.
+///
+/// (Standard "Zero-Sized-Types get to cheat and lie" caveats apply, although it
+/// may be desirable to give them their own API just to make that 100% clear.)
+///
+/// This API and its claimed semantics are part of the Strict Provenance experiment,
+/// see the [module documentation][crate::ptr] for details.
+#[inline(always)]
+#[must_use]
+#[rustc_const_stable(feature = "stable_things_using_strict_provenance", since = "1.61.0")]
+#[unstable(feature = "strict_provenance", issue = "95228")]
+pub const fn invalid_mut<T>(addr: usize) -> *mut T {
+    // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
+    // We use transmute rather than a cast so tools like Miri can tell that this
+    // is *not* the same as from_exposed_addr.
+    // SAFETY: every valid integer is also a valid pointer (as long as you don't dereference that
+    // pointer).
+    unsafe { mem::transmute(addr) }
+}
+
+/// Convert an address back to a pointer, picking up a previously 'exposed' provenance.
+///
+/// This is equivalent to `addr as *const T`. The provenance of the returned pointer is that of *any*
+/// pointer that was previously passed to [`expose_addr`][pointer::expose_addr] or a `ptr as usize`
+/// cast. If there is no previously 'exposed' provenance that justifies the way this pointer will be
+/// used, the program has undefined behavior. Note that there is no algorithm that decides which
+/// provenance will be used. You can think of this as "guessing" the right provenance, and the guess
+/// will be "maximally in your favor", in the sense that if there is any way to avoid undefined
+/// behavior, then that is the guess that will be taken.
+///
+/// On platforms with multiple address spaces, it is your responsibility to ensure that the
+/// address makes sense in the address space that this pointer will be used with.
+///
+/// Using this method means that code is *not* following strict provenance rules. "Guessing" a
+/// suitable provenance complicates specification and reasoning and may not be supported by
+/// tools that help you to stay conformant with the Rust memory model, so it is recommended to
+/// use [`with_addr`][pointer::with_addr] wherever possible.
+///
+/// On most platforms this will produce a value with the same bytes as the address. Platforms
+/// which need to store additional information in a pointer may not support this operation,
+/// since it is generally not possible to actually *compute* which provenance the returned
+/// pointer has to pick up.
+///
+/// This API and its claimed semantics are part of the Strict Provenance experiment, see the
+/// [module documentation][crate::ptr] for details.
+#[must_use]
+#[inline]
+#[unstable(feature = "strict_provenance", issue = "95228")]
+pub fn from_exposed_addr<T>(addr: usize) -> *const T
+where
+    T: Sized,
+{
+    // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
+    addr as *const T
+}
+
+/// Convert an address back to a mutable pointer, picking up a previously 'exposed' provenance.
+///
+/// This is equivalent to `addr as *mut T`. The provenance of the returned pointer is that of *any*
+/// pointer that was previously passed to [`expose_addr`][pointer::expose_addr] or a `ptr as usize`
+/// cast. If there is no previously 'exposed' provenance that justifies the way this pointer will be
+/// used, the program has undefined behavior. Note that there is no algorithm that decides which
+/// provenance will be used. You can think of this as "guessing" the right provenance, and the guess
+/// will be "maximally in your favor", in the sense that if there is any way to avoid undefined
+/// behavior, then that is the guess that will be taken.
+///
+/// On platforms with multiple address spaces, it is your responsibility to ensure that the
+/// address makes sense in the address space that this pointer will be used with.
+///
+/// Using this method means that code is *not* following strict provenance rules. "Guessing" a
+/// suitable provenance complicates specification and reasoning and may not be supported by
+/// tools that help you to stay conformant with the Rust memory model, so it is recommended to
+/// use [`with_addr`][pointer::with_addr] wherever possible.
+///
+/// On most platforms this will produce a value with the same bytes as the address. Platforms
+/// which need to store additional information in a pointer may not support this operation,
+/// since it is generally not possible to actually *compute* which provenance the returned
+/// pointer has to pick up.
+///
+/// This API and its claimed semantics are part of the Strict Provenance experiment, see the
+/// [module documentation][crate::ptr] for details.
+#[must_use]
+#[inline]
+#[unstable(feature = "strict_provenance", issue = "95228")]
+pub fn from_exposed_addr_mut<T>(addr: usize) -> *mut T
+where
+    T: Sized,
+{
+    // FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic.
+    addr as *mut T
+}
+
+/// Creates a null mutable raw pointer.
+///
+/// # Examples
+///
+/// ```
+/// use std::ptr;
+///
+/// let p: *mut i32 = ptr::null_mut();
+/// assert!(p.is_null());
+/// ```
+#[inline(always)]
+#[must_use]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_promotable]
+#[rustc_const_stable(feature = "const_ptr_null", since = "1.24.0")]
+#[rustc_allow_const_fn_unstable(ptr_metadata)]
+#[rustc_diagnostic_item = "ptr_null_mut"]
+pub const fn null_mut<T: ?Sized + Thin>() -> *mut T {
+    from_raw_parts_mut(invalid_mut(0), ())
+}
+
+/// Forms a raw slice from a pointer and a length.
+///
+/// The `len` argument is the number of **elements**, not the number of bytes.
+///
+/// This function is safe, but actually using the return value is unsafe.
+/// See the documentation of [`slice::from_raw_parts`] for slice safety requirements.
+///
+/// [`slice::from_raw_parts`]: crate::slice::from_raw_parts
+///
+/// # Examples
+///
+/// ```rust
+/// use std::ptr;
+///
+/// // create a slice pointer when starting out with a pointer to the first element
+/// let x = [5, 6, 7];
+/// let raw_pointer = x.as_ptr();
+/// let slice = ptr::slice_from_raw_parts(raw_pointer, 3);
+/// assert_eq!(unsafe { &*slice }[2], 7);
+/// ```
+#[inline]
+#[stable(feature = "slice_from_raw_parts", since = "1.42.0")]
+#[rustc_const_stable(feature = "const_slice_from_raw_parts", since = "1.64.0")]
+#[rustc_allow_const_fn_unstable(ptr_metadata)]
+pub const fn slice_from_raw_parts<T>(data: *const T, len: usize) -> *const [T] {
+    from_raw_parts(data.cast(), len)
+}
+
+/// Performs the same functionality as [`slice_from_raw_parts`], except that a
+/// raw mutable slice is returned, as opposed to a raw immutable slice.
+///
+/// See the documentation of [`slice_from_raw_parts`] for more details.
+///
+/// This function is safe, but actually using the return value is unsafe.
+/// See the documentation of [`slice::from_raw_parts_mut`] for slice safety requirements.
+///
+/// [`slice::from_raw_parts_mut`]: crate::slice::from_raw_parts_mut
+///
+/// # Examples
+///
+/// ```rust
+/// use std::ptr;
+///
+/// let x = &mut [5, 6, 7];
+/// let raw_pointer = x.as_mut_ptr();
+/// let slice = ptr::slice_from_raw_parts_mut(raw_pointer, 3);
+///
+/// unsafe {
+///     (*slice)[2] = 99; // assign a value at an index in the slice
+/// };
+///
+/// assert_eq!(unsafe { &*slice }[2], 99);
+/// ```
+#[inline]
+#[stable(feature = "slice_from_raw_parts", since = "1.42.0")]
+#[rustc_const_unstable(feature = "const_slice_from_raw_parts_mut", issue = "67456")]
+pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
+    from_raw_parts_mut(data.cast(), len)
+}
+
+/// Swaps the values at two mutable locations of the same type, without
+/// deinitializing either.
+///
+/// But for the following exceptions, this function is semantically
+/// equivalent to [`mem::swap`]:
+///
+/// * It operates on raw pointers instead of references. When references are
+///   available, [`mem::swap`] should be preferred.
+///
+/// * The two pointed-to values may overlap. If the values do overlap, then the
+///   overlapping region of memory from `x` will be used. This is demonstrated
+///   in the second example below.
+///
+/// * The operation is "untyped" in the sense that data may be uninitialized or otherwise violate
+///   the requirements of `T`. The initialization state is preserved exactly.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * Both `x` and `y` must be [valid] for both reads and writes.
+///
+/// * Both `x` and `y` must be properly aligned.
+///
+/// Note that even if `T` has size `0`, the pointers must be non-null and properly aligned.
+///
+/// [valid]: self#safety
+///
+/// # Examples
+///
+/// Swapping two non-overlapping regions:
+///
+/// ```
+/// use std::ptr;
+///
+/// let mut array = [0, 1, 2, 3];
+///
+/// let (x, y) = array.split_at_mut(2);
+/// let x = x.as_mut_ptr().cast::<[u32; 2]>(); // this is `array[0..2]`
+/// let y = y.as_mut_ptr().cast::<[u32; 2]>(); // this is `array[2..4]`
+///
+/// unsafe {
+///     ptr::swap(x, y);
+///     assert_eq!([2, 3, 0, 1], array);
+/// }
+/// ```
+///
+/// Swapping two overlapping regions:
+///
+/// ```
+/// use std::ptr;
+///
+/// let mut array: [i32; 4] = [0, 1, 2, 3];
+///
+/// let array_ptr: *mut i32 = array.as_mut_ptr();
+///
+/// let x = array_ptr as *mut [i32; 3]; // this is `array[0..3]`
+/// let y = unsafe { array_ptr.add(1) } as *mut [i32; 3]; // this is `array[1..4]`
+///
+/// unsafe {
+///     ptr::swap(x, y);
+///     // The indices `1..3` of the slice overlap between `x` and `y`.
+///     // Reasonable results would be for to them be `[2, 3]`, so that indices `0..3` are
+///     // `[1, 2, 3]` (matching `y` before the `swap`); or for them to be `[0, 1]`
+///     // so that indices `1..4` are `[0, 1, 2]` (matching `x` before the `swap`).
+///     // This implementation is defined to make the latter choice.
+///     assert_eq!([1, 0, 1, 2], array);
+/// }
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
+pub const unsafe fn swap<T>(x: *mut T, y: *mut T) {
+    // Give ourselves some scratch space to work with.
+    // We do not have to worry about drops: `MaybeUninit` does nothing when dropped.
+    let mut tmp = MaybeUninit::<T>::uninit();
+
+    // Perform the swap
+    // SAFETY: the caller must guarantee that `x` and `y` are
+    // valid for writes and properly aligned. `tmp` cannot be
+    // overlapping either `x` or `y` because `tmp` was just allocated
+    // on the stack as a separate allocated object.
+    unsafe {
+        copy_nonoverlapping(x, tmp.as_mut_ptr(), 1);
+        copy(y, x, 1); // `x` and `y` may overlap
+        copy_nonoverlapping(tmp.as_ptr(), y, 1);
+    }
+}
+
+/// Swaps `count * size_of::<T>()` bytes between the two regions of memory
+/// beginning at `x` and `y`. The two regions must *not* overlap.
+///
+/// The operation is "untyped" in the sense that data may be uninitialized or otherwise violate the
+/// requirements of `T`. The initialization state is preserved exactly.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * Both `x` and `y` must be [valid] for both reads and writes of `count *
+///   size_of::<T>()` bytes.
+///
+/// * Both `x` and `y` must be properly aligned.
+///
+/// * The region of memory beginning at `x` with a size of `count *
+///   size_of::<T>()` bytes must *not* overlap with the region of memory
+///   beginning at `y` with the same size.
+///
+/// Note that even if the effectively copied size (`count * size_of::<T>()`) is `0`,
+/// the pointers must be non-null and properly aligned.
+///
+/// [valid]: self#safety
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use std::ptr;
+///
+/// let mut x = [1, 2, 3, 4];
+/// let mut y = [7, 8, 9];
+///
+/// unsafe {
+///     ptr::swap_nonoverlapping(x.as_mut_ptr(), y.as_mut_ptr(), 2);
+/// }
+///
+/// assert_eq!(x, [7, 8, 3, 4]);
+/// assert_eq!(y, [1, 2, 9]);
+/// ```
+#[inline]
+#[stable(feature = "swap_nonoverlapping", since = "1.27.0")]
+#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
+pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
+    #[allow(unused)]
+    macro_rules! attempt_swap_as_chunks {
+        ($ChunkTy:ty) => {
+            if mem::align_of::<T>() >= mem::align_of::<$ChunkTy>()
+                && mem::size_of::<T>() % mem::size_of::<$ChunkTy>() == 0
+            {
+                let x: *mut $ChunkTy = x.cast();
+                let y: *mut $ChunkTy = y.cast();
+                let count = count * (mem::size_of::<T>() / mem::size_of::<$ChunkTy>());
+                // SAFETY: these are the same bytes that the caller promised were
+                // ok, just typed as `MaybeUninit<ChunkTy>`s instead of as `T`s.
+                // The `if` condition above ensures that we're not violating
+                // alignment requirements, and that the division is exact so
+                // that we don't lose any bytes off the end.
+                return unsafe { swap_nonoverlapping_simple_untyped(x, y, count) };
+            }
+        };
+    }
+
+    // SAFETY: the caller must guarantee that `x` and `y` are
+    // valid for writes and properly aligned.
+    unsafe {
+        assert_unsafe_precondition!(
+            is_aligned_and_not_null(x)
+                && is_aligned_and_not_null(y)
+                && is_nonoverlapping(x, y, count)
+        );
+    }
+
+    // NOTE(scottmcm) Miri is disabled here as reading in smaller units is a
+    // pessimization for it.  Also, if the type contains any unaligned pointers,
+    // copying those over multiple reads is difficult to support.
+    #[cfg(not(miri))]
+    {
+        // Split up the slice into small power-of-two-sized chunks that LLVM is able
+        // to vectorize (unless it's a special type with more-than-pointer alignment,
+        // because we don't want to pessimize things like slices of SIMD vectors.)
+        if mem::align_of::<T>() <= mem::size_of::<usize>()
+            && (!mem::size_of::<T>().is_power_of_two()
+                || mem::size_of::<T>() > mem::size_of::<usize>() * 2)
+        {
+            attempt_swap_as_chunks!(usize);
+            attempt_swap_as_chunks!(u8);
+        }
+    }
+
+    // SAFETY: Same preconditions as this function
+    unsafe { swap_nonoverlapping_simple_untyped(x, y, count) }
+}
+
+/// Same behaviour and safety conditions as [`swap_nonoverlapping`]
+///
+/// LLVM can vectorize this (at least it can for the power-of-two-sized types
+/// `swap_nonoverlapping` tries to use) so no need to manually SIMD it.
+#[inline]
+#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
+const unsafe fn swap_nonoverlapping_simple_untyped<T>(x: *mut T, y: *mut T, count: usize) {
+    let x = x.cast::<MaybeUninit<T>>();
+    let y = y.cast::<MaybeUninit<T>>();
+    let mut i = 0;
+    while i < count {
+        // SAFETY: By precondition, `i` is in-bounds because it's below `n`
+        let x = unsafe { &mut *x.add(i) };
+        // SAFETY: By precondition, `i` is in-bounds because it's below `n`
+        // and it's distinct from `x` since the ranges are non-overlapping
+        let y = unsafe { &mut *y.add(i) };
+        mem::swap_simple::<MaybeUninit<T>>(x, y);
+
+        i += 1;
+    }
+}
+
+/// Moves `src` into the pointed `dst`, returning the previous `dst` value.
+///
+/// Neither value is dropped.
+///
+/// This function is semantically equivalent to [`mem::replace`] except that it
+/// operates on raw pointers instead of references. When references are
+/// available, [`mem::replace`] should be preferred.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `dst` must be [valid] for both reads and writes.
+///
+/// * `dst` must be properly aligned.
+///
+/// * `dst` must point to a properly initialized value of type `T`.
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null and properly aligned.
+///
+/// [valid]: self#safety
+///
+/// # Examples
+///
+/// ```
+/// use std::ptr;
+///
+/// let mut rust = vec!['b', 'u', 's', 't'];
+///
+/// // `mem::replace` would have the same effect without requiring the unsafe
+/// // block.
+/// let b = unsafe {
+///     ptr::replace(&mut rust[0], 'r')
+/// };
+///
+/// assert_eq!(b, 'b');
+/// assert_eq!(rust, &['r', 'u', 's', 't']);
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_replace", issue = "83164")]
+pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
+    // SAFETY: the caller must guarantee that `dst` is valid to be
+    // cast to a mutable reference (valid for writes, aligned, initialized),
+    // and cannot overlap `src` since `dst` must point to a distinct
+    // allocated object.
+    unsafe {
+        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        mem::swap(&mut *dst, &mut src); // cannot overlap
+    }
+    src
+}
+
+/// Reads the value from `src` without moving it. This leaves the
+/// memory in `src` unchanged.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `src` must be [valid] for reads.
+///
+/// * `src` must be properly aligned. Use [`read_unaligned`] if this is not the
+///   case.
+///
+/// * `src` must point to a properly initialized value of type `T`.
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null and properly aligned.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// let x = 12;
+/// let y = &x as *const i32;
+///
+/// unsafe {
+///     assert_eq!(std::ptr::read(y), 12);
+/// }
+/// ```
+///
+/// Manually implement [`mem::swap`]:
+///
+/// ```
+/// use std::ptr;
+///
+/// fn swap<T>(a: &mut T, b: &mut T) {
+///     unsafe {
+///         // Create a bitwise copy of the value at `a` in `tmp`.
+///         let tmp = ptr::read(a);
+///
+///         // Exiting at this point (either by explicitly returning or by
+///         // calling a function which panics) would cause the value in `tmp` to
+///         // be dropped while the same value is still referenced by `a`. This
+///         // could trigger undefined behavior if `T` is not `Copy`.
+///
+///         // Create a bitwise copy of the value at `b` in `a`.
+///         // This is safe because mutable references cannot alias.
+///         ptr::copy_nonoverlapping(b, a, 1);
+///
+///         // As above, exiting here could trigger undefined behavior because
+///         // the same value is referenced by `a` and `b`.
+///
+///         // Move `tmp` into `b`.
+///         ptr::write(b, tmp);
+///
+///         // `tmp` has been moved (`write` takes ownership of its second argument),
+///         // so nothing is dropped implicitly here.
+///     }
+/// }
+///
+/// let mut foo = "foo".to_owned();
+/// let mut bar = "bar".to_owned();
+///
+/// swap(&mut foo, &mut bar);
+///
+/// assert_eq!(foo, "bar");
+/// assert_eq!(bar, "foo");
+/// ```
+///
+/// ## Ownership of the Returned Value
+///
+/// `read` creates a bitwise copy of `T`, regardless of whether `T` is [`Copy`].
+/// If `T` is not [`Copy`], using both the returned value and the value at
+/// `*src` can violate memory safety. Note that assigning to `*src` counts as a
+/// use because it will attempt to drop the value at `*src`.
+///
+/// [`write()`] can be used to overwrite data without causing it to be dropped.
+///
+/// ```
+/// use std::ptr;
+///
+/// let mut s = String::from("foo");
+/// unsafe {
+///     // `s2` now points to the same underlying memory as `s`.
+///     let mut s2: String = ptr::read(&s);
+///
+///     assert_eq!(s2, "foo");
+///
+///     // Assigning to `s2` causes its original value to be dropped. Beyond
+///     // this point, `s` must no longer be used, as the underlying memory has
+///     // been freed.
+///     s2 = String::default();
+///     assert_eq!(s2, "");
+///
+///     // Assigning to `s` would cause the old value to be dropped again,
+///     // resulting in undefined behavior.
+///     // s = String::from("bar"); // ERROR
+///
+///     // `ptr::write` can be used to overwrite a value without dropping it.
+///     ptr::write(&mut s, String::from("bar"));
+/// }
+///
+/// assert_eq!(s, "bar");
+/// ```
+///
+/// [valid]: self#safety
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
+pub const unsafe fn read<T>(src: *const T) -> T {
+    // We are calling the intrinsics directly to avoid function calls in the generated code
+    // as `intrinsics::copy_nonoverlapping` is a wrapper function.
+    extern "rust-intrinsic" {
+        #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
+        fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+    }
+
+    let mut tmp = MaybeUninit::<T>::uninit();
+    // SAFETY: the caller must guarantee that `src` is valid for reads.
+    // `src` cannot overlap `tmp` because `tmp` was just allocated on
+    // the stack as a separate allocated object.
+    //
+    // Also, since we just wrote a valid value into `tmp`, it is guaranteed
+    // to be properly initialized.
+    unsafe {
+        copy_nonoverlapping(src, tmp.as_mut_ptr(), 1);
+        tmp.assume_init()
+    }
+}
+
+/// Reads the value from `src` without moving it. This leaves the
+/// memory in `src` unchanged.
+///
+/// Unlike [`read`], `read_unaligned` works with unaligned pointers.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `src` must be [valid] for reads.
+///
+/// * `src` must point to a properly initialized value of type `T`.
+///
+/// Like [`read`], `read_unaligned` creates a bitwise copy of `T`, regardless of
+/// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the returned
+/// value and the value at `*src` can [violate memory safety][read-ownership].
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null.
+///
+/// [read-ownership]: read#ownership-of-the-returned-value
+/// [valid]: self#safety
+///
+/// ## On `packed` structs
+///
+/// Attempting to create a raw pointer to an `unaligned` struct field with
+/// an expression such as `&packed.unaligned as *const FieldType` creates an
+/// intermediate unaligned reference before converting that to a raw pointer.
+/// That this reference is temporary and immediately cast is inconsequential
+/// as the compiler always expects references to be properly aligned.
+/// As a result, using `&packed.unaligned as *const FieldType` causes immediate
+/// *undefined behavior* in your program.
+///
+/// Instead you must use the [`ptr::addr_of!`](addr_of) macro to
+/// create the pointer. You may use that returned pointer together with this
+/// function.
+///
+/// An example of what not to do and how this relates to `read_unaligned` is:
+///
+/// ```
+/// #[repr(packed, C)]
+/// struct Packed {
+///     _padding: u8,
+///     unaligned: u32,
+/// }
+///
+/// let packed = Packed {
+///     _padding: 0x00,
+///     unaligned: 0x01020304,
+/// };
+///
+/// // Take the address of a 32-bit integer which is not aligned.
+/// // In contrast to `&packed.unaligned as *const _`, this has no undefined behavior.
+/// let unaligned = std::ptr::addr_of!(packed.unaligned);
+///
+/// let v = unsafe { std::ptr::read_unaligned(unaligned) };
+/// assert_eq!(v, 0x01020304);
+/// ```
+///
+/// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however.
+///
+/// # Examples
+///
+/// Read a usize value from a byte buffer:
+///
+/// ```
+/// use std::mem;
+///
+/// fn read_usize(x: &[u8]) -> usize {
+///     assert!(x.len() >= mem::size_of::<usize>());
+///
+///     let ptr = x.as_ptr() as *const usize;
+///
+///     unsafe { ptr.read_unaligned() }
+/// }
+/// ```
+#[inline]
+#[stable(feature = "ptr_unaligned", since = "1.17.0")]
+#[rustc_const_unstable(feature = "const_ptr_read", issue = "80377")]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
+pub const unsafe fn read_unaligned<T>(src: *const T) -> T {
+    let mut tmp = MaybeUninit::<T>::uninit();
+    // SAFETY: the caller must guarantee that `src` is valid for reads.
+    // `src` cannot overlap `tmp` because `tmp` was just allocated on
+    // the stack as a separate allocated object.
+    //
+    // Also, since we just wrote a valid value into `tmp`, it is guaranteed
+    // to be properly initialized.
+    unsafe {
+        copy_nonoverlapping(src as *const u8, tmp.as_mut_ptr() as *mut u8, mem::size_of::<T>());
+        tmp.assume_init()
+    }
+}
+
+/// Overwrites a memory location with the given value without reading or
+/// dropping the old value.
+///
+/// `write` does not drop the contents of `dst`. This is safe, but it could leak
+/// allocations or resources, so care should be taken not to overwrite an object
+/// that should be dropped.
+///
+/// Additionally, it does not drop `src`. Semantically, `src` is moved into the
+/// location pointed to by `dst`.
+///
+/// This is appropriate for initializing uninitialized memory, or overwriting
+/// memory that has previously been [`read`] from.
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `dst` must be [valid] for writes.
+///
+/// * `dst` must be properly aligned. Use [`write_unaligned`] if this is not the
+///   case.
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null and properly aligned.
+///
+/// [valid]: self#safety
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// let mut x = 0;
+/// let y = &mut x as *mut i32;
+/// let z = 12;
+///
+/// unsafe {
+///     std::ptr::write(y, z);
+///     assert_eq!(std::ptr::read(y), 12);
+/// }
+/// ```
+///
+/// Manually implement [`mem::swap`]:
+///
+/// ```
+/// use std::ptr;
+///
+/// fn swap<T>(a: &mut T, b: &mut T) {
+///     unsafe {
+///         // Create a bitwise copy of the value at `a` in `tmp`.
+///         let tmp = ptr::read(a);
+///
+///         // Exiting at this point (either by explicitly returning or by
+///         // calling a function which panics) would cause the value in `tmp` to
+///         // be dropped while the same value is still referenced by `a`. This
+///         // could trigger undefined behavior if `T` is not `Copy`.
+///
+///         // Create a bitwise copy of the value at `b` in `a`.
+///         // This is safe because mutable references cannot alias.
+///         ptr::copy_nonoverlapping(b, a, 1);
+///
+///         // As above, exiting here could trigger undefined behavior because
+///         // the same value is referenced by `a` and `b`.
+///
+///         // Move `tmp` into `b`.
+///         ptr::write(b, tmp);
+///
+///         // `tmp` has been moved (`write` takes ownership of its second argument),
+///         // so nothing is dropped implicitly here.
+///     }
+/// }
+///
+/// let mut foo = "foo".to_owned();
+/// let mut bar = "bar".to_owned();
+///
+/// swap(&mut foo, &mut bar);
+///
+/// assert_eq!(foo, "bar");
+/// assert_eq!(bar, "foo");
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
+pub const unsafe fn write<T>(dst: *mut T, src: T) {
+    // We are calling the intrinsics directly to avoid function calls in the generated code
+    // as `intrinsics::copy_nonoverlapping` is a wrapper function.
+    extern "rust-intrinsic" {
+        #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
+        fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+    }
+
+    // SAFETY: the caller must guarantee that `dst` is valid for writes.
+    // `dst` cannot overlap `src` because the caller has mutable access
+    // to `dst` while `src` is owned by this function.
+    unsafe {
+        copy_nonoverlapping(&src as *const T, dst, 1);
+        intrinsics::forget(src);
+    }
+}
+
+/// Overwrites a memory location with the given value without reading or
+/// dropping the old value.
+///
+/// Unlike [`write()`], the pointer may be unaligned.
+///
+/// `write_unaligned` does not drop the contents of `dst`. This is safe, but it
+/// could leak allocations or resources, so care should be taken not to overwrite
+/// an object that should be dropped.
+///
+/// Additionally, it does not drop `src`. Semantically, `src` is moved into the
+/// location pointed to by `dst`.
+///
+/// This is appropriate for initializing uninitialized memory, or overwriting
+/// memory that has previously been read with [`read_unaligned`].
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `dst` must be [valid] for writes.
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null.
+///
+/// [valid]: self#safety
+///
+/// ## On `packed` structs
+///
+/// Attempting to create a raw pointer to an `unaligned` struct field with
+/// an expression such as `&packed.unaligned as *const FieldType` creates an
+/// intermediate unaligned reference before converting that to a raw pointer.
+/// That this reference is temporary and immediately cast is inconsequential
+/// as the compiler always expects references to be properly aligned.
+/// As a result, using `&packed.unaligned as *const FieldType` causes immediate
+/// *undefined behavior* in your program.
+///
+/// Instead you must use the [`ptr::addr_of_mut!`](addr_of_mut)
+/// macro to create the pointer. You may use that returned pointer together with
+/// this function.
+///
+/// An example of how to do it and how this relates to `write_unaligned` is:
+///
+/// ```
+/// #[repr(packed, C)]
+/// struct Packed {
+///     _padding: u8,
+///     unaligned: u32,
+/// }
+///
+/// let mut packed: Packed = unsafe { std::mem::zeroed() };
+///
+/// // Take the address of a 32-bit integer which is not aligned.
+/// // In contrast to `&packed.unaligned as *mut _`, this has no undefined behavior.
+/// let unaligned = std::ptr::addr_of_mut!(packed.unaligned);
+///
+/// unsafe { std::ptr::write_unaligned(unaligned, 42) };
+///
+/// assert_eq!({packed.unaligned}, 42); // `{...}` forces copying the field instead of creating a reference.
+/// ```
+///
+/// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however
+/// (as can be seen in the `assert_eq!` above).
+///
+/// # Examples
+///
+/// Write a usize value to a byte buffer:
+///
+/// ```
+/// use std::mem;
+///
+/// fn write_usize(x: &mut [u8], val: usize) {
+///     assert!(x.len() >= mem::size_of::<usize>());
+///
+///     let ptr = x.as_mut_ptr() as *mut usize;
+///
+///     unsafe { ptr.write_unaligned(val) }
+/// }
+/// ```
+#[inline]
+#[stable(feature = "ptr_unaligned", since = "1.17.0")]
+#[rustc_const_unstable(feature = "const_ptr_write", issue = "86302")]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
+pub const unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
+    // SAFETY: the caller must guarantee that `dst` is valid for writes.
+    // `dst` cannot overlap `src` because the caller has mutable access
+    // to `dst` while `src` is owned by this function.
+    unsafe {
+        copy_nonoverlapping(&src as *const T as *const u8, dst as *mut u8, mem::size_of::<T>());
+        // We are calling the intrinsic directly to avoid function calls in the generated code.
+        intrinsics::forget(src);
+    }
+}
+
+/// Performs a volatile read of the value from `src` without moving it. This
+/// leaves the memory in `src` unchanged.
+///
+/// Volatile operations are intended to act on I/O memory, and are guaranteed
+/// to not be elided or reordered by the compiler across other volatile
+/// operations.
+///
+/// # Notes
+///
+/// Rust does not currently have a rigorously and formally defined memory model,
+/// so the precise semantics of what "volatile" means here is subject to change
+/// over time. That being said, the semantics will almost always end up pretty
+/// similar to [C11's definition of volatile][c11].
+///
+/// The compiler shouldn't change the relative order or number of volatile
+/// memory operations. However, volatile memory operations on zero-sized types
+/// (e.g., if a zero-sized type is passed to `read_volatile`) are noops
+/// and may be ignored.
+///
+/// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `src` must be [valid] for reads.
+///
+/// * `src` must be properly aligned.
+///
+/// * `src` must point to a properly initialized value of type `T`.
+///
+/// Like [`read`], `read_volatile` creates a bitwise copy of `T`, regardless of
+/// whether `T` is [`Copy`]. If `T` is not [`Copy`], using both the returned
+/// value and the value at `*src` can [violate memory safety][read-ownership].
+/// However, storing non-[`Copy`] types in volatile memory is almost certainly
+/// incorrect.
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null and properly aligned.
+///
+/// [valid]: self#safety
+/// [read-ownership]: read#ownership-of-the-returned-value
+///
+/// Just like in C, whether an operation is volatile has no bearing whatsoever
+/// on questions involving concurrent access from multiple threads. Volatile
+/// accesses behave exactly like non-atomic accesses in that regard. In particular,
+/// a race between a `read_volatile` and any write operation to the same location
+/// is undefined behavior.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// let x = 12;
+/// let y = &x as *const i32;
+///
+/// unsafe {
+///     assert_eq!(std::ptr::read_volatile(y), 12);
+/// }
+/// ```
+#[inline]
+#[stable(feature = "volatile", since = "1.9.0")]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
+pub unsafe fn read_volatile<T>(src: *const T) -> T {
+    // SAFETY: the caller must uphold the safety contract for `volatile_load`.
+    unsafe {
+        assert_unsafe_precondition!(is_aligned_and_not_null(src));
+        intrinsics::volatile_load(src)
+    }
+}
+
+/// Performs a volatile write of a memory location with the given value without
+/// reading or dropping the old value.
+///
+/// Volatile operations are intended to act on I/O memory, and are guaranteed
+/// to not be elided or reordered by the compiler across other volatile
+/// operations.
+///
+/// `write_volatile` does not drop the contents of `dst`. This is safe, but it
+/// could leak allocations or resources, so care should be taken not to overwrite
+/// an object that should be dropped.
+///
+/// Additionally, it does not drop `src`. Semantically, `src` is moved into the
+/// location pointed to by `dst`.
+///
+/// # Notes
+///
+/// Rust does not currently have a rigorously and formally defined memory model,
+/// so the precise semantics of what "volatile" means here is subject to change
+/// over time. That being said, the semantics will almost always end up pretty
+/// similar to [C11's definition of volatile][c11].
+///
+/// The compiler shouldn't change the relative order or number of volatile
+/// memory operations. However, volatile memory operations on zero-sized types
+/// (e.g., if a zero-sized type is passed to `write_volatile`) are noops
+/// and may be ignored.
+///
+/// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
+///
+/// # Safety
+///
+/// Behavior is undefined if any of the following conditions are violated:
+///
+/// * `dst` must be [valid] for writes.
+///
+/// * `dst` must be properly aligned.
+///
+/// Note that even if `T` has size `0`, the pointer must be non-null and properly aligned.
+///
+/// [valid]: self#safety
+///
+/// Just like in C, whether an operation is volatile has no bearing whatsoever
+/// on questions involving concurrent access from multiple threads. Volatile
+/// accesses behave exactly like non-atomic accesses in that regard. In particular,
+/// a race between a `write_volatile` and any other operation (reading or writing)
+/// on the same location is undefined behavior.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// let mut x = 0;
+/// let y = &mut x as *mut i32;
+/// let z = 12;
+///
+/// unsafe {
+///     std::ptr::write_volatile(y, z);
+///     assert_eq!(std::ptr::read_volatile(y), 12);
+/// }
+/// ```
+#[inline]
+#[stable(feature = "volatile", since = "1.9.0")]
+#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
+pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
+    // SAFETY: the caller must uphold the safety contract for `volatile_store`.
+    unsafe {
+        assert_unsafe_precondition!(is_aligned_and_not_null(dst));
+        intrinsics::volatile_store(dst, src);
+    }
+}
+
+/// Align pointer `p`.
+///
+/// Calculate offset (in terms of elements of `stride` stride) that has to be applied
+/// to pointer `p` so that pointer `p` would get aligned to `a`.
+///
+/// Note: This implementation has been carefully tailored to not panic. It is UB for this to panic.
+/// The only real change that can be made here is change of `INV_TABLE_MOD_16` and associated
+/// constants.
+///
+/// If we ever decide to make it possible to call the intrinsic with `a` that is not a
+/// power-of-two, it will probably be more prudent to just change to a naive implementation rather
+/// than trying to adapt this to accommodate that change.
+///
+/// Any questions go to @nagisa.
+#[lang = "align_offset"]
+pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
+    // FIXME(#75598): Direct use of these intrinsics improves codegen significantly at opt-level <=
+    // 1, where the method versions of these operations are not inlined.
+    use intrinsics::{
+        cttz_nonzero, exact_div, unchecked_rem, unchecked_shl, unchecked_shr, unchecked_sub,
+        wrapping_add, wrapping_mul, wrapping_sub,
+    };
+
+    /// Calculate multiplicative modular inverse of `x` modulo `m`.
+    ///
+    /// This implementation is tailored for `align_offset` and has following preconditions:
+    ///
+    /// * `m` is a power-of-two;
+    /// * `x < m`; (if `x ≥ m`, pass in `x % m` instead)
+    ///
+    /// Implementation of this function shall not panic. Ever.
+    #[inline]
+    unsafe fn mod_inv(x: usize, m: usize) -> usize {
+        /// Multiplicative modular inverse table modulo 2⁴ = 16.
+        ///
+        /// Note, that this table does not contain values where inverse does not exist (i.e., for
+        /// `0⁻¹ mod 16`, `2⁻¹ mod 16`, etc.)
+        const INV_TABLE_MOD_16: [u8; 8] = [1, 11, 13, 7, 9, 3, 5, 15];
+        /// Modulo for which the `INV_TABLE_MOD_16` is intended.
+        const INV_TABLE_MOD: usize = 16;
+        /// INV_TABLE_MOD²
+        const INV_TABLE_MOD_SQUARED: usize = INV_TABLE_MOD * INV_TABLE_MOD;
+
+        let table_inverse = INV_TABLE_MOD_16[(x & (INV_TABLE_MOD - 1)) >> 1] as usize;
+        // SAFETY: `m` is required to be a power-of-two, hence non-zero.
+        let m_minus_one = unsafe { unchecked_sub(m, 1) };
+        if m <= INV_TABLE_MOD {
+            table_inverse & m_minus_one
+        } else {
+            // We iterate "up" using the following formula:
+            //
+            // $$ xy ≡ 1 (mod 2ⁿ) → xy (2 - xy) ≡ 1 (mod 2²ⁿ) $$
+            //
+            // until 2²ⁿ ≥ m. Then we can reduce to our desired `m` by taking the result `mod m`.
+            let mut inverse = table_inverse;
+            let mut going_mod = INV_TABLE_MOD_SQUARED;
+            loop {
+                // y = y * (2 - xy) mod n
+                //
+                // Note, that we use wrapping operations here intentionally – the original formula
+                // uses e.g., subtraction `mod n`. It is entirely fine to do them `mod
+                // usize::MAX` instead, because we take the result `mod n` at the end
+                // anyway.
+                inverse = wrapping_mul(inverse, wrapping_sub(2usize, wrapping_mul(x, inverse)));
+                if going_mod >= m {
+                    return inverse & m_minus_one;
+                }
+                going_mod = wrapping_mul(going_mod, going_mod);
+            }
+        }
+    }
+
+    let addr = p.addr();
+    let stride = mem::size_of::<T>();
+    // SAFETY: `a` is a power-of-two, therefore non-zero.
+    let a_minus_one = unsafe { unchecked_sub(a, 1) };
+
+    if stride == 0 {
+        // SPECIAL_CASE: handle 0-sized types. No matter how many times we step, the address will
+        // stay the same, so no offset will be able to align the pointer unless it is already
+        // aligned. This branch _will_ be optimized out as `stride` is known at compile-time.
+        let p_mod_a = addr & a_minus_one;
+        return if p_mod_a == 0 { 0 } else { usize::MAX };
+    }
+
+    // SAFETY: `stride == 0` case has been handled by the special case above.
+    let a_mod_stride = unsafe { unchecked_rem(a, stride) };
+    if a_mod_stride == 0 {
+        // SPECIAL_CASE: In cases where the `a` is divisible by `stride`, byte offset to align a
+        // pointer can be computed more simply through `-p (mod a)`. In the off-chance the byte
+        // offset is not a multiple of `stride`, the input pointer was misaligned and no pointer
+        // offset will be able to produce a `p` aligned to the specified `a`.
+        //
+        // The naive `-p (mod a)` equation  inhibits LLVM's ability to select instructions
+        // like `lea`. We compute `(round_up_to_next_alignment(p, a) - p)` instead. This
+        // redistributes operations around the load-bearing, but pessimizing `and` instruction
+        // sufficiently for LLVM to be able to utilize the various optimizations it knows about.
+        //
+        // LLVM handles the branch here particularly nicely. If this branch needs to be evaluated
+        // at runtime, it will produce a mask `if addr_mod_stride == 0 { 0 } else { usize::MAX }`
+        // in a branch-free way and then bitwise-OR it with whatever result the `-p mod a`
+        // computation produces.
+
+        // SAFETY: `stride == 0` case has been handled by the special case above.
+        let addr_mod_stride = unsafe { unchecked_rem(addr, stride) };
+
+        return if addr_mod_stride == 0 {
+            let aligned_address = wrapping_add(addr, a_minus_one) & wrapping_sub(0, a);
+            let byte_offset = wrapping_sub(aligned_address, addr);
+            // SAFETY: `stride` is non-zero. This is guaranteed to divide exactly as well, because
+            // addr has been verified to be aligned to the original type’s alignment requirements.
+            unsafe { exact_div(byte_offset, stride) }
+        } else {
+            usize::MAX
+        };
+    }
+
+    // GENERAL_CASE: From here on we’re handling the very general case where `addr` may be
+    // misaligned, there isn’t an obvious relationship between `stride` and `a` that we can take an
+    // advantage of, etc. This case produces machine code that isn’t particularly high quality,
+    // compared to the special cases above. The code produced here is still within the realm of
+    // miracles, given the situations this case has to deal with.
+
+    // SAFETY: a is power-of-two hence non-zero. stride == 0 case is handled above.
+    let gcdpow = unsafe { cttz_nonzero(stride).min(cttz_nonzero(a)) };
+    // SAFETY: gcdpow has an upper-bound that’s at most the number of bits in a usize.
+    let gcd = unsafe { unchecked_shl(1usize, gcdpow) };
+    // SAFETY: gcd is always greater or equal to 1.
+    if addr & unsafe { unchecked_sub(gcd, 1) } == 0 {
+        // This branch solves for the following linear congruence equation:
+        //
+        // ` p + so = 0 mod a `
+        //
+        // `p` here is the pointer value, `s` - stride of `T`, `o` offset in `T`s, and `a` - the
+        // requested alignment.
+        //
+        // With `g = gcd(a, s)`, and the above condition asserting that `p` is also divisible by
+        // `g`, we can denote `a' = a/g`, `s' = s/g`, `p' = p/g`, then this becomes equivalent to:
+        //
+        // ` p' + s'o = 0 mod a' `
+        // ` o = (a' - (p' mod a')) * (s'^-1 mod a') `
+        //
+        // The first term is "the relative alignment of `p` to `a`" (divided by the `g`), the
+        // second term is "how does incrementing `p` by `s` bytes change the relative alignment of
+        // `p`" (again divided by `g`). Division by `g` is necessary to make the inverse well
+        // formed if `a` and `s` are not co-prime.
+        //
+        // Furthermore, the result produced by this solution is not "minimal", so it is necessary
+        // to take the result `o mod lcm(s, a)`. This `lcm(s, a)` is the same as `a'`.
+
+        // SAFETY: `gcdpow` has an upper-bound not greater than the number of trailing 0-bits in
+        // `a`.
+        let a2 = unsafe { unchecked_shr(a, gcdpow) };
+        // SAFETY: `a2` is non-zero. Shifting `a` by `gcdpow` cannot shift out any of the set bits
+        // in `a` (of which it has exactly one).
+        let a2minus1 = unsafe { unchecked_sub(a2, 1) };
+        // SAFETY: `gcdpow` has an upper-bound not greater than the number of trailing 0-bits in
+        // `a`.
+        let s2 = unsafe { unchecked_shr(stride & a_minus_one, gcdpow) };
+        // SAFETY: `gcdpow` has an upper-bound not greater than the number of trailing 0-bits in
+        // `a`. Furthermore, the subtraction cannot overflow, because `a2 = a >> gcdpow` will
+        // always be strictly greater than `(p % a) >> gcdpow`.
+        let minusp2 = unsafe { unchecked_sub(a2, unchecked_shr(addr & a_minus_one, gcdpow)) };
+        // SAFETY: `a2` is a power-of-two, as proven above. `s2` is strictly less than `a2`
+        // because `(s % a) >> gcdpow` is strictly less than `a >> gcdpow`.
+        return wrapping_mul(minusp2, unsafe { mod_inv(s2, a2) }) & a2minus1;
+    }
+
+    // Cannot be aligned at all.
+    usize::MAX
+}
+
+/// Compares raw pointers for equality.
+///
+/// This is the same as using the `==` operator, but less generic:
+/// the arguments have to be `*const T` raw pointers,
+/// not anything that implements `PartialEq`.
+///
+/// This can be used to compare `&T` references (which coerce to `*const T` implicitly)
+/// by their address rather than comparing the values they point to
+/// (which is what the `PartialEq for &T` implementation does).
+///
+/// # Examples
+///
+/// ```
+/// use std::ptr;
+///
+/// let five = 5;
+/// let other_five = 5;
+/// let five_ref = &five;
+/// let same_five_ref = &five;
+/// let other_five_ref = &other_five;
+///
+/// assert!(five_ref == same_five_ref);
+/// assert!(ptr::eq(five_ref, same_five_ref));
+///
+/// assert!(five_ref == other_five_ref);
+/// assert!(!ptr::eq(five_ref, other_five_ref));
+/// ```
+///
+/// Slices are also compared by their length (fat pointers):
+///
+/// ```
+/// let a = [1, 2, 3];
+/// assert!(std::ptr::eq(&a[..3], &a[..3]));
+/// assert!(!std::ptr::eq(&a[..2], &a[..3]));
+/// assert!(!std::ptr::eq(&a[0..2], &a[1..3]));
+/// ```
+///
+/// Traits are also compared by their implementation:
+///
+/// ```
+/// #[repr(transparent)]
+/// struct Wrapper { member: i32 }
+///
+/// trait Trait {}
+/// impl Trait for Wrapper {}
+/// impl Trait for i32 {}
+///
+/// let wrapper = Wrapper { member: 10 };
+///
+/// // Pointers have equal addresses.
+/// assert!(std::ptr::eq(
+///     &wrapper as *const Wrapper as *const u8,
+///     &wrapper.member as *const i32 as *const u8
+/// ));
+///
+/// // Objects have equal addresses, but `Trait` has different implementations.
+/// assert!(!std::ptr::eq(
+///     &wrapper as &dyn Trait,
+///     &wrapper.member as &dyn Trait,
+/// ));
+/// assert!(!std::ptr::eq(
+///     &wrapper as &dyn Trait as *const dyn Trait,
+///     &wrapper.member as &dyn Trait as *const dyn Trait,
+/// ));
+///
+/// // Converting the reference to a `*const u8` compares by address.
+/// assert!(std::ptr::eq(
+///     &wrapper as &dyn Trait as *const dyn Trait as *const u8,
+///     &wrapper.member as &dyn Trait as *const dyn Trait as *const u8,
+/// ));
+/// ```
+#[stable(feature = "ptr_eq", since = "1.17.0")]
+#[inline]
+pub fn eq<T: ?Sized>(a: *const T, b: *const T) -> bool {
+    a == b
+}
+
+/// Hash a raw pointer.
+///
+/// This can be used to hash a `&T` reference (which coerces to `*const T` implicitly)
+/// by its address rather than the value it points to
+/// (which is what the `Hash for &T` implementation does).
+///
+/// # Examples
+///
+/// ```
+/// use std::collections::hash_map::DefaultHasher;
+/// use std::hash::{Hash, Hasher};
+/// use std::ptr;
+///
+/// let five = 5;
+/// let five_ref = &five;
+///
+/// let mut hasher = DefaultHasher::new();
+/// ptr::hash(five_ref, &mut hasher);
+/// let actual = hasher.finish();
+///
+/// let mut hasher = DefaultHasher::new();
+/// (five_ref as *const i32).hash(&mut hasher);
+/// let expected = hasher.finish();
+///
+/// assert_eq!(actual, expected);
+/// ```
+#[stable(feature = "ptr_hash", since = "1.35.0")]
+pub fn hash<T: ?Sized, S: hash::Hasher>(hashee: *const T, into: &mut S) {
+    use crate::hash::Hash;
+    hashee.hash(into);
+}
+
+// If this is a unary fn pointer, it adds a doc comment.
+// Otherwise, it hides the docs entirely.
+macro_rules! maybe_fnptr_doc {
+    (@ #[$meta:meta] $item:item) => {
+        #[doc(hidden)]
+        #[$meta]
+        $item
+    };
+    ($a:ident @ #[$meta:meta] $item:item) => {
+        #[cfg_attr(not(bootstrap), doc(fake_variadic))]
+        #[doc = "This trait is implemented for function pointers with up to twelve arguments."]
+        #[$meta]
+        $item
+    };
+    ($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
+        #[doc(hidden)]
+        #[$meta]
+        $item
+    };
+}
+
+// FIXME(strict_provenance_magic): function pointers have buggy codegen that
+// necessitates casting to a usize to get the backend to do the right thing.
+// for now I will break AVR to silence *a billion* lints. We should probably
+// have a proper "opaque function pointer type" to handle this kind of thing.
+
+// Impls for function pointers
+macro_rules! fnptr_impls_safety_abi {
+    ($FnTy: ty, $($Arg: ident),*) => {
+        maybe_fnptr_doc! {
+            $($Arg)* @
+            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            impl<Ret, $($Arg),*> PartialEq for $FnTy {
+                #[inline]
+                fn eq(&self, other: &Self) -> bool {
+                    *self as usize == *other as usize
+                }
+            }
+        }
+
+        maybe_fnptr_doc! {
+            $($Arg)* @
+            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            impl<Ret, $($Arg),*> Eq for $FnTy {}
+        }
+
+        maybe_fnptr_doc! {
+            $($Arg)* @
+            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            impl<Ret, $($Arg),*> PartialOrd for $FnTy {
+                #[inline]
+                fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+                    (*self as usize).partial_cmp(&(*other as usize))
+                }
+            }
+        }
+
+        maybe_fnptr_doc! {
+            $($Arg)* @
+            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            impl<Ret, $($Arg),*> Ord for $FnTy {
+                #[inline]
+                fn cmp(&self, other: &Self) -> Ordering {
+                    (*self as usize).cmp(&(*other as usize))
+                }
+            }
+        }
+
+        maybe_fnptr_doc! {
+            $($Arg)* @
+            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            impl<Ret, $($Arg),*> hash::Hash for $FnTy {
+                fn hash<HH: hash::Hasher>(&self, state: &mut HH) {
+                    state.write_usize(*self as usize)
+                }
+            }
+        }
+
+        maybe_fnptr_doc! {
+            $($Arg)* @
+            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            impl<Ret, $($Arg),*> fmt::Pointer for $FnTy {
+                fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                    fmt::pointer_fmt_inner(*self as usize, f)
+                }
+            }
+        }
+
+        maybe_fnptr_doc! {
+            $($Arg)* @
+            #[stable(feature = "fnptr_impls", since = "1.4.0")]
+            impl<Ret, $($Arg),*> fmt::Debug for $FnTy {
+                fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                    fmt::pointer_fmt_inner(*self as usize, f)
+                }
+            }
+        }
+    }
+}
+
+macro_rules! fnptr_impls_args {
+    ($($Arg: ident),+) => {
+        fnptr_impls_safety_abi! { extern "Rust" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { extern "C" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { extern "C" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { unsafe extern "Rust" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),+) -> Ret, $($Arg),+ }
+        fnptr_impls_safety_abi! { unsafe extern "C" fn($($Arg),+ , ...) -> Ret, $($Arg),+ }
+    };
+    () => {
+        // No variadic functions with 0 parameters
+        fnptr_impls_safety_abi! { extern "Rust" fn() -> Ret, }
+        fnptr_impls_safety_abi! { extern "C" fn() -> Ret, }
+        fnptr_impls_safety_abi! { unsafe extern "Rust" fn() -> Ret, }
+        fnptr_impls_safety_abi! { unsafe extern "C" fn() -> Ret, }
+    };
+}
+
+fnptr_impls_args! {}
+fnptr_impls_args! { T }
+fnptr_impls_args! { A, B }
+fnptr_impls_args! { A, B, C }
+fnptr_impls_args! { A, B, C, D }
+fnptr_impls_args! { A, B, C, D, E }
+fnptr_impls_args! { A, B, C, D, E, F }
+fnptr_impls_args! { A, B, C, D, E, F, G }
+fnptr_impls_args! { A, B, C, D, E, F, G, H }
+fnptr_impls_args! { A, B, C, D, E, F, G, H, I }
+fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J }
+fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K }
+fnptr_impls_args! { A, B, C, D, E, F, G, H, I, J, K, L }
+
+/// Create a `const` raw pointer to a place, without creating an intermediate reference.
+///
+/// Creating a reference with `&`/`&mut` is only allowed if the pointer is properly aligned
+/// and points to initialized data. For cases where those requirements do not hold,
+/// raw pointers should be used instead. However, `&expr as *const _` creates a reference
+/// before casting it to a raw pointer, and that reference is subject to the same rules
+/// as all other references. This macro can create a raw pointer *without* creating
+/// a reference first.
+///
+/// Note, however, that the `expr` in `addr_of!(expr)` is still subject to all
+/// the usual rules. In particular, `addr_of!(*ptr::null())` is Undefined
+/// Behavior because it dereferences a null pointer.
+///
+/// # Example
+///
+/// ```
+/// use std::ptr;
+///
+/// #[repr(packed)]
+/// struct Packed {
+///     f1: u8,
+///     f2: u16,
+/// }
+///
+/// let packed = Packed { f1: 1, f2: 2 };
+/// // `&packed.f2` would create an unaligned reference, and thus be Undefined Behavior!
+/// let raw_f2 = ptr::addr_of!(packed.f2);
+/// assert_eq!(unsafe { raw_f2.read_unaligned() }, 2);
+/// ```
+///
+/// See [`addr_of_mut`] for how to create a pointer to unininitialized data.
+/// Doing that with `addr_of` would not make much sense since one could only
+/// read the data, and that would be Undefined Behavior.
+#[stable(feature = "raw_ref_macros", since = "1.51.0")]
+#[rustc_macro_transparency = "semitransparent"]
+#[allow_internal_unstable(raw_ref_op)]
+pub macro addr_of($place:expr) {
+    &raw const $place
+}
+
+/// Create a `mut` raw pointer to a place, without creating an intermediate reference.
+///
+/// Creating a reference with `&`/`&mut` is only allowed if the pointer is properly aligned
+/// and points to initialized data. For cases where those requirements do not hold,
+/// raw pointers should be used instead. However, `&mut expr as *mut _` creates a reference
+/// before casting it to a raw pointer, and that reference is subject to the same rules
+/// as all other references. This macro can create a raw pointer *without* creating
+/// a reference first.
+///
+/// Note, however, that the `expr` in `addr_of_mut!(expr)` is still subject to all
+/// the usual rules. In particular, `addr_of_mut!(*ptr::null_mut())` is Undefined
+/// Behavior because it dereferences a null pointer.
+///
+/// # Examples
+///
+/// **Creating a pointer to unaligned data:**
+///
+/// ```
+/// use std::ptr;
+///
+/// #[repr(packed)]
+/// struct Packed {
+///     f1: u8,
+///     f2: u16,
+/// }
+///
+/// let mut packed = Packed { f1: 1, f2: 2 };
+/// // `&mut packed.f2` would create an unaligned reference, and thus be Undefined Behavior!
+/// let raw_f2 = ptr::addr_of_mut!(packed.f2);
+/// unsafe { raw_f2.write_unaligned(42); }
+/// assert_eq!({packed.f2}, 42); // `{...}` forces copying the field instead of creating a reference.
+/// ```
+///
+/// **Creating a pointer to uninitialized data:**
+///
+/// ```rust
+/// use std::{ptr, mem::MaybeUninit};
+///
+/// struct Demo {
+///     field: bool,
+/// }
+///
+/// let mut uninit = MaybeUninit::<Demo>::uninit();
+/// // `&uninit.as_mut().field` would create a reference to an uninitialized `bool`,
+/// // and thus be Undefined Behavior!
+/// let f1_ptr = unsafe { ptr::addr_of_mut!((*uninit.as_mut_ptr()).field) };
+/// unsafe { f1_ptr.write(true); }
+/// let init = unsafe { uninit.assume_init() };
+/// ```
+#[stable(feature = "raw_ref_macros", since = "1.51.0")]
+#[rustc_macro_transparency = "semitransparent"]
+#[allow_internal_unstable(raw_ref_op)]
+pub macro addr_of_mut($place:expr) {
+    &raw mut $place
+}