Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 1825 insertions, 0 deletions

diff --git a/rust/zerocopy/src/macros.rs b/rust/zerocopy/src/macros.rs
new file mode 100644
index 000000000..ec67c03a4
--- /dev/null
+++ b/rust/zerocopy/src/macros.rs
@@ -0,0 +1,1825 @@
+// SPDX-License-Identifier: (BSD-2-Clause OR Apache-2.0) OR MIT
+//
+// Copyright 2024 The Fuchsia Authors
+//
+// Licensed under the 2-Clause BSD License <LICENSE-BSD or
+// https://opensource.org/license/bsd-2-clause>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+/// Safely transmutes a value of one type to a value of another type of the same
+/// size.
+///
+/// This macro behaves like an invocation of this function:
+///
+/// ```ignore
+/// const fn transmute<Src, Dst>(src: Src) -> Dst
+/// where
+///     Src: IntoBytes,
+///     Dst: FromBytes,
+///     size_of::<Src>() == size_of::<Dst>(),
+/// {
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// However, unlike a function, this macro can only be invoked when the types of
+/// `Src` and `Dst` are completely concrete. The types `Src` and `Dst` are
+/// inferred from the calling context; they cannot be explicitly specified in
+/// the macro invocation.
+///
+/// Note that the `Src` produced by the expression `$e` will *not* be dropped.
+/// Semantically, its bits will be copied into a new value of type `Dst`, the
+/// original `Src` will be forgotten, and the value of type `Dst` will be
+/// returned.
+///
+/// # `#![allow(shrink)]`
+///
+/// If `#![allow(shrink)]` is provided, `transmute!` additionally supports
+/// transmutations that shrink the size of the value; e.g.:
+///
+/// ```
+/// # use zerocopy::transmute;
+/// let u: u32 = transmute!(#![allow(shrink)] 0u64);
+/// assert_eq!(u, 0u32);
+/// ```
+///
+/// # Examples
+///
+/// ```
+/// # use zerocopy::transmute;
+/// let one_dimensional: [u8; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
+///
+/// let two_dimensional: [[u8; 4]; 2] = transmute!(one_dimensional);
+///
+/// assert_eq!(two_dimensional, [[0, 1, 2, 3], [4, 5, 6, 7]]);
+/// ```
+///
+/// # Use in `const` contexts
+///
+/// This macro can be invoked in `const` contexts.
+///
+#[doc = codegen_section!(
+    header = "h2",
+    bench = "transmute",
+    format = "coco_static_size",
+)]
+#[macro_export]
+macro_rules! transmute {
+    // NOTE: This must be a macro (rather than a function with trait bounds)
+    // because there's no way, in a generic context, to enforce that two types
+    // have the same size. `core::mem::transmute` uses compiler magic to enforce
+    // this so long as the types are concrete.
+    (#![allow(shrink)] $e:expr) => {{
+        let mut e = $e;
+        if false {
+            // This branch, though never taken, ensures that the type of `e` is
+            // `IntoBytes` and that the type of the  outer macro invocation
+            // expression is `FromBytes`.
+
+            fn transmute<Src, Dst>(src: Src) -> Dst
+            where
+                Src: $crate::IntoBytes,
+                Dst: $crate::FromBytes,
+            {
+                let _ = src;
+                loop {}
+            }
+            loop {}
+            #[allow(unreachable_code)]
+            transmute(e)
+        } else {
+            use $crate::util::macro_util::core_reexport::mem::ManuallyDrop;
+
+            // NOTE: `repr(packed)` is important! It ensures that the size of
+            // `Transmute` won't be rounded up to accommodate `Src`'s or `Dst`'s
+            // alignment, which would break the size comparison logic below.
+            //
+            // As an example of why this is problematic, consider `Src = [u8;
+            // 5]`, `Dst = u32`. The total size of `Transmute<Src, Dst>` would
+            // be 8, and so we would reject a `[u8; 5]` to `u32` transmute as
+            // being size-increasing, which it isn't.
+            #[repr(C, packed)]
+            union Transmute<Src, Dst> {
+                src: ManuallyDrop<Src>,
+                dst: ManuallyDrop<Dst>,
+            }
+
+            // SAFETY: `Transmute` is a `repr(C)` union whose `src` field has
+            // type `ManuallyDrop<Src>`. Thus, the `src` field starts at byte
+            // offset 0 within `Transmute` [1]. `ManuallyDrop<T>` has the same
+            // layout and bit validity as `T`, so it is sound to transmute `Src`
+            // to `Transmute`.
+            //
+            // [1] https://doc.rust-lang.org/1.85.0/reference/type-layout.html#reprc-unions
+            //
+            // [2] Per https://doc.rust-lang.org/1.85.0/std/mem/struct.ManuallyDrop.html:
+            //
+            //   `ManuallyDrop<T>` is guaranteed to have the same layout and bit
+            //   validity as `T`
+            let u: Transmute<_, _> = unsafe {
+                // Clippy: We can't annotate the types; this macro is designed
+                // to infer the types from the calling context.
+                #[allow(clippy::missing_transmute_annotations)]
+                $crate::util::macro_util::core_reexport::mem::transmute(e)
+            };
+
+            if false {
+                // SAFETY: This code is never executed.
+                e = ManuallyDrop::into_inner(unsafe { u.src });
+                // Suppress the `unused_assignments` lint on the previous line.
+                let _ = e;
+                loop {}
+            } else {
+                // SAFETY: Per the safety comment on `let u` above, the `dst`
+                // field in `Transmute` starts at byte offset 0, and has the
+                // same layout and bit validity as `Dst`.
+                //
+                // Transmuting `Src` to `Transmute<Src, Dst>` above using
+                // `core::mem::transmute` ensures that `size_of::<Src>() ==
+                // size_of::<Transmute<Src, Dst>>()`. A `#[repr(C, packed)]`
+                // union has the maximum size of all of its fields [1], so this
+                // is equivalent to `size_of::<Src>() >= size_of::<Dst>()`.
+                //
+                // The outer `if`'s `false` branch ensures that `Src: IntoBytes`
+                // and `Dst: FromBytes`. This, combined with the size bound,
+                // ensures that this transmute is sound.
+                //
+                // [1] Per https://doc.rust-lang.org/1.85.0/reference/type-layout.html#reprc-unions:
+                //
+                //   The union will have a size of the maximum size of all of
+                //   its fields rounded to its alignment
+                let dst = unsafe { u.dst };
+                $crate::util::macro_util::must_use(ManuallyDrop::into_inner(dst))
+            }
+        }
+    }};
+    ($e:expr) => {{
+        let e = $e;
+        if false {
+            // This branch, though never taken, ensures that the type of `e` is
+            // `IntoBytes` and that the type of the  outer macro invocation
+            // expression is `FromBytes`.
+
+            fn transmute<Src, Dst>(src: Src) -> Dst
+            where
+                Src: $crate::IntoBytes,
+                Dst: $crate::FromBytes,
+            {
+                let _ = src;
+                loop {}
+            }
+            loop {}
+            #[allow(unreachable_code)]
+            transmute(e)
+        } else {
+            // SAFETY: `core::mem::transmute` ensures that the type of `e` and
+            // the type of this macro invocation expression have the same size.
+            // We know this transmute is safe thanks to the `IntoBytes` and
+            // `FromBytes` bounds enforced by the `false` branch.
+            let u = unsafe {
+                // Clippy: We can't annotate the types; this macro is designed
+                // to infer the types from the calling context.
+                #[allow(clippy::missing_transmute_annotations, unnecessary_transmutes)]
+                $crate::util::macro_util::core_reexport::mem::transmute(e)
+            };
+            $crate::util::macro_util::must_use(u)
+        }
+    }};
+}
+
+/// Safely transmutes a mutable or immutable reference of one type to an
+/// immutable reference of another type of the same size and compatible
+/// alignment.
+///
+/// This macro behaves like an invocation of this function:
+///
+/// ```ignore
+/// fn transmute_ref<'src, 'dst, Src, Dst>(src: &'src Src) -> &'dst Dst
+/// where
+///     'src: 'dst,
+///     Src: IntoBytes + Immutable + ?Sized,
+///     Dst: FromBytes + Immutable + ?Sized,
+///     align_of::<Src>() >= align_of::<Dst>(),
+///     size_compatible::<Src, Dst>(),
+/// {
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// The types `Src` and `Dst` are inferred from the calling context; they cannot
+/// be explicitly specified in the macro invocation.
+///
+/// # Size compatibility
+///
+/// `transmute_ref!` supports transmuting between `Sized` types, between unsized
+/// (i.e., `?Sized`) types, and from a `Sized` type to an unsized type. It
+/// supports any transmutation that preserves the number of bytes of the
+/// referent, even if doing so requires updating the metadata stored in an
+/// unsized "fat" reference:
+///
+/// ```
+/// # use zerocopy::transmute_ref;
+/// # use core::mem::size_of_val; // Not in the prelude on our MSRV
+/// let src: &[[u8; 2]] = &[[0, 1], [2, 3]][..];
+/// let dst: &[u8] = transmute_ref!(src);
+///
+/// assert_eq!(src.len(), 2);
+/// assert_eq!(dst.len(), 4);
+/// assert_eq!(dst, [0, 1, 2, 3]);
+/// assert_eq!(size_of_val(src), size_of_val(dst));
+/// ```
+///
+/// # Errors
+///
+/// Violations of the alignment and size compatibility checks are detected
+/// *after* the compiler performs monomorphization. This has two important
+/// consequences.
+///
+/// First, it means that generic code will *never* fail these conditions:
+///
+/// ```
+/// # use zerocopy::{transmute_ref, FromBytes, IntoBytes, Immutable};
+/// fn transmute_ref<Src, Dst>(src: &Src) -> &Dst
+/// where
+///     Src: IntoBytes + Immutable,
+///     Dst: FromBytes + Immutable,
+/// {
+///     transmute_ref!(src)
+/// }
+/// ```
+///
+/// Instead, failures will only be detected once generic code is instantiated
+/// with concrete types:
+///
+/// ```compile_fail,E0080
+/// # use zerocopy::{transmute_ref, FromBytes, IntoBytes, Immutable};
+/// #
+/// # fn transmute_ref<Src, Dst>(src: &Src) -> &Dst
+/// # where
+/// #     Src: IntoBytes + Immutable,
+/// #     Dst: FromBytes + Immutable,
+/// # {
+/// #     transmute_ref!(src)
+/// # }
+/// let src: &u16 = &0;
+/// let dst: &u8 = transmute_ref(src);
+/// ```
+///
+/// Second, the fact that violations are detected after monomorphization means
+/// that `cargo check` will usually not detect errors, even when types are
+/// concrete. Instead, `cargo build` must be used to detect such errors.
+///
+/// # Examples
+///
+/// Transmuting between `Sized` types:
+///
+/// ```
+/// # use zerocopy::transmute_ref;
+/// let one_dimensional: [u8; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
+///
+/// let two_dimensional: &[[u8; 4]; 2] = transmute_ref!(&one_dimensional);
+///
+/// assert_eq!(two_dimensional, &[[0, 1, 2, 3], [4, 5, 6, 7]]);
+/// ```
+///
+/// Transmuting between unsized types:
+///
+/// ```
+/// # use {zerocopy::*, zerocopy_derive::*};
+/// # type u16 = zerocopy::byteorder::native_endian::U16;
+/// # type u32 = zerocopy::byteorder::native_endian::U32;
+/// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
+/// #[repr(C)]
+/// struct SliceDst<T, U> {
+///     t: T,
+///     u: [U],
+/// }
+///
+/// type Src = SliceDst<u32, u16>;
+/// type Dst = SliceDst<u16, u8>;
+///
+/// let src = Src::ref_from_bytes(&[0, 1, 2, 3, 4, 5, 6, 7]).unwrap();
+/// let dst: &Dst = transmute_ref!(src);
+///
+/// assert_eq!(src.t.as_bytes(), [0, 1, 2, 3]);
+/// assert_eq!(src.u.len(), 2);
+/// assert_eq!(src.u.as_bytes(), [4, 5, 6, 7]);
+///
+/// assert_eq!(dst.t.as_bytes(), [0, 1]);
+/// assert_eq!(dst.u, [2, 3, 4, 5, 6, 7]);
+/// ```
+///
+/// # Use in `const` contexts
+///
+/// This macro can be invoked in `const` contexts only when `Src: Sized` and
+/// `Dst: Sized`.
+///
+#[doc = codegen_section!(
+    header = "h2",
+    bench = "transmute_ref",
+    format = "coco",
+    arity = 2,
+    [
+        open
+        @index 1
+        @title "Sized"
+        @variant "static_size"
+    ],
+    [
+        @index 2
+        @title "Unsized"
+        @variant "dynamic_size"
+    ]
+)]
+#[macro_export]
+macro_rules! transmute_ref {
+    ($e:expr) => {{
+        // NOTE: This must be a macro (rather than a function with trait bounds)
+        // because there's no way, in a generic context, to enforce that two
+        // types have the same size or alignment.
+
+        // Ensure that the source type is a reference or a mutable reference
+        // (note that mutable references are implicitly reborrowed here).
+        let e: &_ = $e;
+
+        #[allow(unused, clippy::diverging_sub_expression)]
+        if false {
+            // This branch, though never taken, ensures that the type of `e` is
+            // `&T` where `T: IntoBytes + Immutable`, and that the type of this
+            // macro expression is `&U` where `U: FromBytes + Immutable`.
+
+            struct AssertSrcIsIntoBytes<'a, T: ?::core::marker::Sized + $crate::IntoBytes>(&'a T);
+            struct AssertSrcIsImmutable<'a, T: ?::core::marker::Sized + $crate::Immutable>(&'a T);
+            struct AssertDstIsFromBytes<'a, U: ?::core::marker::Sized + $crate::FromBytes>(&'a U);
+            struct AssertDstIsImmutable<'a, T: ?::core::marker::Sized + $crate::Immutable>(&'a T);
+
+            let _ = AssertSrcIsIntoBytes(e);
+            let _ = AssertSrcIsImmutable(e);
+
+            if true {
+                #[allow(unused, unreachable_code)]
+                let u = AssertDstIsFromBytes(loop {});
+                u.0
+            } else {
+                #[allow(unused, unreachable_code)]
+                let u = AssertDstIsImmutable(loop {});
+                u.0
+            }
+        } else {
+            use $crate::util::macro_util::TransmuteRefDst;
+            let t = $crate::util::macro_util::Wrap::new(e);
+
+            if false {
+                // This branch exists solely to force the compiler to infer the
+                // type of `Dst` *before* it attempts to resolve the method call
+                // to `transmute_ref` in the `else` branch.
+                //
+                // Without this, if `Src` is `Sized` but `Dst` is `!Sized`, the
+                // compiler will eagerly select the inherent impl of
+                // `transmute_ref` (which requires `Dst: Sized`) because inherent
+                // methods take priority over trait methods. It does this before
+                // it realizes `Dst` is `!Sized`, leading to a compile error when
+                // it checks the bounds later.
+                //
+                // By calling this helper (which returns `&Dst`), we force `Dst`
+                // to be fully resolved. By the time it gets to the `else`
+                // branch, the compiler knows `Dst` is `!Sized`, properly
+                // disqualifies the inherent method, and falls back to the trait
+                // implementation.
+                t.transmute_ref_inference_helper()
+            } else {
+                // SAFETY: The outer `if false` branch ensures that:
+                // - `Src: IntoBytes + Immutable`
+                // - `Dst: FromBytes + Immutable`
+                unsafe {
+                    t.transmute_ref()
+                }
+            }
+        }
+    }}
+}
+
+/// Safely transmutes a mutable reference of one type to a mutable reference of
+/// another type of the same size and compatible alignment.
+///
+/// This macro behaves like an invocation of this function:
+///
+/// ```ignore
+/// const fn transmute_mut<'src, 'dst, Src, Dst>(src: &'src mut Src) -> &'dst mut Dst
+/// where
+///     'src: 'dst,
+///     Src: FromBytes + IntoBytes + ?Sized,
+///     Dst: FromBytes + IntoBytes + ?Sized,
+///     align_of::<Src>() >= align_of::<Dst>(),
+///     size_compatible::<Src, Dst>(),
+/// {
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// The types `Src` and `Dst` are inferred from the calling context; they cannot
+/// be explicitly specified in the macro invocation.
+///
+/// # Size compatibility
+///
+/// `transmute_mut!` supports transmuting between `Sized` types, between unsized
+/// (i.e., `?Sized`) types, and from a `Sized` type to an unsized type. It
+/// supports any transmutation that preserves the number of bytes of the
+/// referent, even if doing so requires updating the metadata stored in an
+/// unsized "fat" reference:
+///
+/// ```
+/// # use zerocopy::transmute_mut;
+/// # use core::mem::size_of_val; // Not in the prelude on our MSRV
+/// let src: &mut [[u8; 2]] = &mut [[0, 1], [2, 3]][..];
+/// let dst: &mut [u8] = transmute_mut!(src);
+///
+/// assert_eq!(dst.len(), 4);
+/// assert_eq!(dst, [0, 1, 2, 3]);
+/// let dst_size = size_of_val(dst);
+/// assert_eq!(src.len(), 2);
+/// assert_eq!(size_of_val(src), dst_size);
+/// ```
+///
+/// # Errors
+///
+/// Violations of the alignment and size compatibility checks are detected
+/// *after* the compiler performs monomorphization. This has two important
+/// consequences.
+///
+/// First, it means that generic code will *never* fail these conditions:
+///
+/// ```
+/// # use zerocopy::{transmute_mut, FromBytes, IntoBytes, Immutable};
+/// fn transmute_mut<Src, Dst>(src: &mut Src) -> &mut Dst
+/// where
+///     Src: FromBytes + IntoBytes,
+///     Dst: FromBytes + IntoBytes,
+/// {
+///     transmute_mut!(src)
+/// }
+/// ```
+///
+/// Instead, failures will only be detected once generic code is instantiated
+/// with concrete types:
+///
+/// ```compile_fail,E0080
+/// # use zerocopy::{transmute_mut, FromBytes, IntoBytes, Immutable};
+/// #
+/// # fn transmute_mut<Src, Dst>(src: &mut Src) -> &mut Dst
+/// # where
+/// #     Src: FromBytes + IntoBytes,
+/// #     Dst: FromBytes + IntoBytes,
+/// # {
+/// #     transmute_mut!(src)
+/// # }
+/// let src: &mut u16 = &mut 0;
+/// let dst: &mut u8 = transmute_mut(src);
+/// ```
+///
+/// Second, the fact that violations are detected after monomorphization means
+/// that `cargo check` will usually not detect errors, even when types are
+/// concrete. Instead, `cargo build` must be used to detect such errors.
+///
+///
+/// # Examples
+///
+/// Transmuting between `Sized` types:
+///
+/// ```
+/// # use zerocopy::transmute_mut;
+/// let mut one_dimensional: [u8; 8] = [0, 1, 2, 3, 4, 5, 6, 7];
+///
+/// let two_dimensional: &mut [[u8; 4]; 2] = transmute_mut!(&mut one_dimensional);
+///
+/// assert_eq!(two_dimensional, &[[0, 1, 2, 3], [4, 5, 6, 7]]);
+///
+/// two_dimensional.reverse();
+///
+/// assert_eq!(one_dimensional, [4, 5, 6, 7, 0, 1, 2, 3]);
+/// ```
+///
+/// Transmuting between unsized types:
+///
+/// ```
+/// # use {zerocopy::*, zerocopy_derive::*};
+/// # type u16 = zerocopy::byteorder::native_endian::U16;
+/// # type u32 = zerocopy::byteorder::native_endian::U32;
+/// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
+/// #[repr(C)]
+/// struct SliceDst<T, U> {
+///     t: T,
+///     u: [U],
+/// }
+///
+/// type Src = SliceDst<u32, u16>;
+/// type Dst = SliceDst<u16, u8>;
+///
+/// let mut bytes = [0, 1, 2, 3, 4, 5, 6, 7];
+/// let src = Src::mut_from_bytes(&mut bytes[..]).unwrap();
+/// let dst: &mut Dst = transmute_mut!(src);
+///
+/// assert_eq!(dst.t.as_bytes(), [0, 1]);
+/// assert_eq!(dst.u, [2, 3, 4, 5, 6, 7]);
+///
+/// assert_eq!(src.t.as_bytes(), [0, 1, 2, 3]);
+/// assert_eq!(src.u.len(), 2);
+/// assert_eq!(src.u.as_bytes(), [4, 5, 6, 7]);
+/// ```
+#[macro_export]
+macro_rules! transmute_mut {
+    ($e:expr) => {{
+        // NOTE: This must be a macro (rather than a function with trait bounds)
+        // because, for backwards-compatibility on v0.8.x, we use the autoref
+        // specialization trick to dispatch to different `transmute_mut`
+        // implementations: one which doesn't require `Src: KnownLayout + Dst:
+        // KnownLayout` when `Src: Sized + Dst: Sized`, and one which requires
+        // `KnownLayout` bounds otherwise.
+
+        // Ensure that the source type is a mutable reference.
+        let e: &mut _ = $e;
+
+        #[allow(unused)]
+        use $crate::util::macro_util::TransmuteMutDst as _;
+        let t = $crate::util::macro_util::Wrap::new(e);
+        if false {
+            // This branch exists solely to force the compiler to infer the type
+            // of `Dst` *before* it attempts to resolve the method call to
+            // `transmute_mut` in the `else` branch.
+            //
+            // Without this, if `Src` is `Sized` but `Dst` is `!Sized`, the
+            // compiler will eagerly select the inherent impl of `transmute_mut`
+            // (which requires `Dst: Sized`) because inherent methods take
+            // priority over trait methods. It does this before it realizes
+            // `Dst` is `!Sized`, leading to a compile error when it checks the
+            // bounds later.
+            //
+            // By calling this helper (which returns `&mut Dst`), we force `Dst`
+            // to be fully resolved. By the time it gets to the `else` branch,
+            // the compiler knows `Dst` is `!Sized`, properly disqualifies the
+            // inherent method, and falls back to the trait implementation.
+            t.transmute_mut_inference_helper()
+        } else {
+            t.transmute_mut()
+        }
+    }}
+}
+
+/// Conditionally transmutes a value of one type to a value of another type of
+/// the same size.
+///
+/// This macro behaves like an invocation of this function:
+///
+/// ```ignore
+/// fn try_transmute<Src, Dst>(src: Src) -> Result<Dst, ValidityError<Src, Dst>>
+/// where
+///     Src: IntoBytes,
+///     Dst: TryFromBytes,
+///     size_of::<Src>() == size_of::<Dst>(),
+/// {
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// However, unlike a function, this macro can only be invoked when the types of
+/// `Src` and `Dst` are completely concrete. The types `Src` and `Dst` are
+/// inferred from the calling context; they cannot be explicitly specified in
+/// the macro invocation.
+///
+/// Note that the `Src` produced by the expression `$e` will *not* be dropped.
+/// Semantically, its bits will be copied into a new value of type `Dst`, the
+/// original `Src` will be forgotten, and the value of type `Dst` will be
+/// returned.
+///
+/// # Examples
+///
+/// ```
+/// # use zerocopy::*;
+/// // 0u8 → bool = false
+/// assert_eq!(try_transmute!(0u8), Ok(false));
+///
+/// // 1u8 → bool = true
+///  assert_eq!(try_transmute!(1u8), Ok(true));
+///
+/// // 2u8 → bool = error
+/// assert!(matches!(
+///     try_transmute!(2u8),
+///     Result::<bool, _>::Err(ValidityError { .. })
+/// ));
+/// ```
+///
+#[doc = codegen_section!(
+    header = "h2",
+    bench = "try_transmute",
+    format = "coco_static_size",
+)]
+#[macro_export]
+macro_rules! try_transmute {
+    ($e:expr) => {{
+        // NOTE: This must be a macro (rather than a function with trait bounds)
+        // because there's no way, in a generic context, to enforce that two
+        // types have the same size. `core::mem::transmute` uses compiler magic
+        // to enforce this so long as the types are concrete.
+
+        let e = $e;
+        if false {
+            // Check that the sizes of the source and destination types are
+            // equal.
+
+            // SAFETY: This code is never executed.
+            Ok(unsafe {
+                // Clippy: We can't annotate the types; this macro is designed
+                // to infer the types from the calling context.
+                #[allow(clippy::missing_transmute_annotations)]
+                $crate::util::macro_util::core_reexport::mem::transmute(e)
+            })
+        } else {
+            $crate::util::macro_util::try_transmute::<_, _>(e)
+        }
+    }}
+}
+
+/// Conditionally transmutes a mutable or immutable reference of one type to an
+/// immutable reference of another type of the same size and compatible
+/// alignment.
+///
+/// *Note that while the **value** of the referent is checked for validity at
+/// runtime, the **size** and **alignment** are checked at compile time. For
+/// conversions which are fallible with respect to size and alignment, see the
+/// methods on [`TryFromBytes`].*
+///
+/// This macro behaves like an invocation of this function:
+///
+/// ```ignore
+/// fn try_transmute_ref<Src, Dst>(src: &Src) -> Result<&Dst, ValidityError<&Src, Dst>>
+/// where
+///     Src: IntoBytes + Immutable + ?Sized,
+///     Dst: TryFromBytes + Immutable + ?Sized,
+///     align_of::<Src>() >= align_of::<Dst>(),
+///     size_compatible::<Src, Dst>(),
+/// {
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// The types `Src` and `Dst` are inferred from the calling context; they cannot
+/// be explicitly specified in the macro invocation.
+///
+/// [`TryFromBytes`]: crate::TryFromBytes
+///
+/// # Size compatibility
+///
+/// `try_transmute_ref!` supports transmuting between `Sized` types, between
+/// unsized (i.e., `?Sized`) types, and from a `Sized` type to an unsized type.
+/// It supports any transmutation that preserves the number of bytes of the
+/// referent, even if doing so requires updating the metadata stored in an
+/// unsized "fat" reference:
+///
+/// ```
+/// # use zerocopy::try_transmute_ref;
+/// # use core::mem::size_of_val; // Not in the prelude on our MSRV
+/// let src: &[[u8; 2]] = &[[0, 1], [2, 3]][..];
+/// let dst: &[u8] = try_transmute_ref!(src).unwrap();
+///
+/// assert_eq!(src.len(), 2);
+/// assert_eq!(dst.len(), 4);
+/// assert_eq!(dst, [0, 1, 2, 3]);
+/// assert_eq!(size_of_val(src), size_of_val(dst));
+/// ```
+///
+/// # Examples
+///
+/// Transmuting between `Sized` types:
+///
+/// ```
+/// # use zerocopy::*;
+/// // 0u8 → bool = false
+/// assert_eq!(try_transmute_ref!(&0u8), Ok(&false));
+///
+/// // 1u8 → bool = true
+///  assert_eq!(try_transmute_ref!(&1u8), Ok(&true));
+///
+/// // 2u8 → bool = error
+/// assert!(matches!(
+///     try_transmute_ref!(&2u8),
+///     Result::<&bool, _>::Err(ValidityError { .. })
+/// ));
+/// ```
+///
+/// Transmuting between unsized types:
+///
+/// ```
+/// # use {zerocopy::*, zerocopy_derive::*};
+/// # type u16 = zerocopy::byteorder::native_endian::U16;
+/// # type u32 = zerocopy::byteorder::native_endian::U32;
+/// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
+/// #[repr(C)]
+/// struct SliceDst<T, U> {
+///     t: T,
+///     u: [U],
+/// }
+///
+/// type Src = SliceDst<u32, u16>;
+/// type Dst = SliceDst<u16, bool>;
+///
+/// let src = Src::ref_from_bytes(&[0, 1, 0, 1, 0, 1, 0, 1]).unwrap();
+/// let dst: &Dst = try_transmute_ref!(src).unwrap();
+///
+/// assert_eq!(src.t.as_bytes(), [0, 1, 0, 1]);
+/// assert_eq!(src.u.len(), 2);
+/// assert_eq!(src.u.as_bytes(), [0, 1, 0, 1]);
+///
+/// assert_eq!(dst.t.as_bytes(), [0, 1]);
+/// assert_eq!(dst.u, [false, true, false, true, false, true]);
+/// ```
+///
+#[doc = codegen_section!(
+    header = "h2",
+    bench = "try_transmute_ref",
+    format = "coco",
+    arity = 2,
+    [
+        open
+        @index 1
+        @title "Sized"
+        @variant "static_size"
+    ],
+    [
+        @index 2
+        @title "Unsized"
+        @variant "dynamic_size"
+    ]
+)]
+#[macro_export]
+macro_rules! try_transmute_ref {
+    ($e:expr) => {{
+        // Ensure that the source type is a reference or a mutable reference
+        // (note that mutable references are implicitly reborrowed here).
+        let e: &_ = $e;
+
+        #[allow(unused_imports)]
+        use $crate::util::macro_util::TryTransmuteRefDst as _;
+        let t = $crate::util::macro_util::Wrap::new(e);
+        if false {
+            // This branch exists solely to force the compiler to infer the type
+            // of `Dst` *before* it attempts to resolve the method call to
+            // `try_transmute_ref` in the `else` branch.
+            //
+            // Without this, if `Src` is `Sized` but `Dst` is `!Sized`, the
+            // compiler will eagerly select the inherent impl of
+            // `try_transmute_ref` (which requires `Dst: Sized`) because
+            // inherent methods take priority over trait methods. It does this
+            // before it realizes `Dst` is `!Sized`, leading to a compile error
+            // when it checks the bounds later.
+            //
+            // By calling this helper (which returns `&Dst`), we force `Dst`
+            // to be fully resolved. By the time it gets to the `else`
+            // branch, the compiler knows `Dst` is `!Sized`, properly
+            // disqualifies the inherent method, and falls back to the trait
+            // implementation.
+            Ok(t.transmute_ref_inference_helper())
+        } else {
+            t.try_transmute_ref()
+        }
+    }}
+}
+
+/// Conditionally transmutes a mutable reference of one type to a mutable
+/// reference of another type of the same size and compatible alignment.
+///
+/// *Note that while the **value** of the referent is checked for validity at
+/// runtime, the **size** and **alignment** are checked at compile time. For
+/// conversions which are fallible with respect to size and alignment, see the
+/// methods on [`TryFromBytes`].*
+///
+/// This macro behaves like an invocation of this function:
+///
+/// ```ignore
+/// fn try_transmute_mut<Src, Dst>(src: &mut Src) -> Result<&mut Dst, ValidityError<&mut Src, Dst>>
+/// where
+///     Src: FromBytes + IntoBytes + ?Sized,
+///     Dst: TryFromBytes + IntoBytes + ?Sized,
+///     align_of::<Src>() >= align_of::<Dst>(),
+///     size_compatible::<Src, Dst>(),
+/// {
+/// # /*
+///     ...
+/// # */
+/// }
+/// ```
+///
+/// The types `Src` and `Dst` are inferred from the calling context; they cannot
+/// be explicitly specified in the macro invocation.
+///
+/// [`TryFromBytes`]: crate::TryFromBytes
+///
+/// # Size compatibility
+///
+/// `try_transmute_mut!` supports transmuting between `Sized` types, between
+/// unsized (i.e., `?Sized`) types, and from a `Sized` type to an unsized type.
+/// It supports any transmutation that preserves the number of bytes of the
+/// referent, even if doing so requires updating the metadata stored in an
+/// unsized "fat" reference:
+///
+/// ```
+/// # use zerocopy::try_transmute_mut;
+/// # use core::mem::size_of_val; // Not in the prelude on our MSRV
+/// let src: &mut [[u8; 2]] = &mut [[0, 1], [2, 3]][..];
+/// let dst: &mut [u8] = try_transmute_mut!(src).unwrap();
+///
+/// assert_eq!(dst.len(), 4);
+/// assert_eq!(dst, [0, 1, 2, 3]);
+/// let dst_size = size_of_val(dst);
+/// assert_eq!(src.len(), 2);
+/// assert_eq!(size_of_val(src), dst_size);
+/// ```
+///
+/// # Examples
+///
+/// Transmuting between `Sized` types:
+///
+/// ```
+/// # use zerocopy::*;
+/// // 0u8 → bool = false
+/// let src = &mut 0u8;
+/// assert_eq!(try_transmute_mut!(src), Ok(&mut false));
+///
+/// // 1u8 → bool = true
+/// let src = &mut 1u8;
+///  assert_eq!(try_transmute_mut!(src), Ok(&mut true));
+///
+/// // 2u8 → bool = error
+/// let src = &mut 2u8;
+/// assert!(matches!(
+///     try_transmute_mut!(src),
+///     Result::<&mut bool, _>::Err(ValidityError { .. })
+/// ));
+/// ```
+///
+/// Transmuting between unsized types:
+///
+/// ```
+/// # use {zerocopy::*, zerocopy_derive::*};
+/// # type u16 = zerocopy::byteorder::native_endian::U16;
+/// # type u32 = zerocopy::byteorder::native_endian::U32;
+/// #[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
+/// #[repr(C)]
+/// struct SliceDst<T, U> {
+///     t: T,
+///     u: [U],
+/// }
+///
+/// type Src = SliceDst<u32, u16>;
+/// type Dst = SliceDst<u16, bool>;
+///
+/// let mut bytes = [0, 1, 0, 1, 0, 1, 0, 1];
+/// let src = Src::mut_from_bytes(&mut bytes).unwrap();
+///
+/// assert_eq!(src.t.as_bytes(), [0, 1, 0, 1]);
+/// assert_eq!(src.u.len(), 2);
+/// assert_eq!(src.u.as_bytes(), [0, 1, 0, 1]);
+///
+/// let dst: &Dst = try_transmute_mut!(src).unwrap();
+///
+/// assert_eq!(dst.t.as_bytes(), [0, 1]);
+/// assert_eq!(dst.u, [false, true, false, true, false, true]);
+/// ```
+#[macro_export]
+macro_rules! try_transmute_mut {
+    ($e:expr) => {{
+        // Ensure that the source type is a mutable reference.
+        let e: &mut _ = $e;
+
+        #[allow(unused_imports)]
+        use $crate::util::macro_util::TryTransmuteMutDst as _;
+        let t = $crate::util::macro_util::Wrap::new(e);
+        if false {
+            // This branch exists solely to force the compiler to infer the type
+            // of `Dst` *before* it attempts to resolve the method call to
+            // `try_transmute_mut` in the `else` branch.
+            //
+            // Without this, if `Src` is `Sized` but `Dst` is `!Sized`, the
+            // compiler will eagerly select the inherent impl of
+            // `try_transmute_mut` (which requires `Dst: Sized`) because
+            // inherent methods take priority over trait methods. It does this
+            // before it realizes `Dst` is `!Sized`, leading to a compile error
+            // when it checks the bounds later.
+            //
+            // By calling this helper (which returns `&Dst`), we force `Dst`
+            // to be fully resolved. By the time it gets to the `else`
+            // branch, the compiler knows `Dst` is `!Sized`, properly
+            // disqualifies the inherent method, and falls back to the trait
+            // implementation.
+            Ok(t.transmute_mut_inference_helper())
+        } else {
+            t.try_transmute_mut()
+        }
+    }}
+}
+
+/// Includes a file and safely transmutes it to a value of an arbitrary type.
+///
+/// The file will be included as a byte array, `[u8; N]`, which will be
+/// transmuted to another type, `T`. `T` is inferred from the calling context,
+/// and must implement [`FromBytes`].
+///
+/// The file is located relative to the current file (similarly to how modules
+/// are found). The provided path is interpreted in a platform-specific way at
+/// compile time. So, for instance, an invocation with a Windows path containing
+/// backslashes `\` would not compile correctly on Unix.
+///
+/// `include_value!` is ignorant of byte order. For byte order-aware types, see
+/// the [`byteorder`] module.
+///
+/// [`FromBytes`]: crate::FromBytes
+/// [`byteorder`]: crate::byteorder
+///
+/// # Examples
+///
+/// Assume there are two files in the same directory with the following
+/// contents:
+///
+/// File `data` (no trailing newline):
+///
+/// ```text
+/// abcd
+/// ```
+///
+/// File `main.rs`:
+///
+/// ```rust
+/// use zerocopy::include_value;
+/// # macro_rules! include_value {
+/// # ($file:expr) => { zerocopy::include_value!(concat!("../testdata/include_value/", $file)) };
+/// # }
+///
+/// fn main() {
+///     let as_u32: u32 = include_value!("data");
+///     assert_eq!(as_u32, u32::from_ne_bytes([b'a', b'b', b'c', b'd']));
+///     let as_i32: i32 = include_value!("data");
+///     assert_eq!(as_i32, i32::from_ne_bytes([b'a', b'b', b'c', b'd']));
+/// }
+/// ```
+///
+/// # Use in `const` contexts
+///
+/// This macro can be invoked in `const` contexts.
+#[doc(alias("include_bytes", "include_data", "include_type"))]
+#[macro_export]
+macro_rules! include_value {
+    ($file:expr $(,)?) => {
+        $crate::transmute!(*::core::include_bytes!($file))
+    };
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! cryptocorrosion_derive_traits {
+    (
+        #[repr($repr:ident)]
+        $(#[$attr:meta])*
+        $vis:vis struct $name:ident $(<$($tyvar:ident),*>)?
+        $(
+            (
+                $($tuple_field_vis:vis $tuple_field_ty:ty),*
+            );
+        )?
+
+        $(
+            {
+                $($field_vis:vis $field_name:ident: $field_ty:ty,)*
+            }
+        )?
+    ) => {
+        $crate::cryptocorrosion_derive_traits!(@assert_allowed_struct_repr #[repr($repr)]);
+
+        $(#[$attr])*
+        #[repr($repr)]
+        $vis struct $name $(<$($tyvar),*>)?
+        $(
+            (
+                $($tuple_field_vis $tuple_field_ty),*
+            );
+        )?
+
+        $(
+            {
+                $($field_vis $field_name: $field_ty,)*
+            }
+        )?
+
+        // SAFETY: See inline.
+        unsafe impl $(<$($tyvar),*>)? $crate::TryFromBytes for $name$(<$($tyvar),*>)?
+        where
+            $(
+                $($tuple_field_ty: $crate::FromBytes,)*
+            )?
+
+            $(
+                $($field_ty: $crate::FromBytes,)*
+            )?
+        {
+            #[inline(always)]
+            fn is_bit_valid<A>(_: $crate::Maybe<'_, Self, A>) -> bool
+            where
+                A: $crate::invariant::Alignment,
+            {
+                // SAFETY: This macro only accepts `#[repr(C)]` and
+                // `#[repr(transparent)]` structs, and this `impl` block
+                // requires all field types to be `FromBytes`. Thus, all
+                // initialized byte sequences constitutes valid instances of
+                // `Self`.
+                true
+            }
+
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` and
+        // `#[repr(transparent)]` structs, and this `impl` block requires all
+        // field types to be `FromBytes`, which is a sub-trait of `FromZeros`.
+        unsafe impl $(<$($tyvar),*>)? $crate::FromZeros for $name$(<$($tyvar),*>)?
+        where
+            $(
+                $($tuple_field_ty: $crate::FromBytes,)*
+            )?
+
+            $(
+                $($field_ty: $crate::FromBytes,)*
+            )?
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` and
+        // `#[repr(transparent)]` structs, and this `impl` block requires all
+        // field types to be `FromBytes`.
+        unsafe impl $(<$($tyvar),*>)? $crate::FromBytes for $name$(<$($tyvar),*>)?
+        where
+            $(
+                $($tuple_field_ty: $crate::FromBytes,)*
+            )?
+
+            $(
+                $($field_ty: $crate::FromBytes,)*
+            )?
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` and
+        // `#[repr(transparent)]` structs, this `impl` block requires all field
+        // types to be `IntoBytes`, and a padding check is used to ensures that
+        // there are no padding bytes.
+        unsafe impl $(<$($tyvar),*>)? $crate::IntoBytes for $name$(<$($tyvar),*>)?
+        where
+            $(
+                $($tuple_field_ty: $crate::IntoBytes,)*
+            )?
+
+            $(
+                $($field_ty: $crate::IntoBytes,)*
+            )?
+
+            (): $crate::util::macro_util::PaddingFree<
+                Self,
+                {
+                    $crate::cryptocorrosion_derive_traits!(
+                        @struct_padding_check #[repr($repr)]
+                        $(($($tuple_field_ty),*))?
+                        $({$($field_ty),*})?
+                    )
+                },
+            >,
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` and
+        // `#[repr(transparent)]` structs, and this `impl` block requires all
+        // field types to be `Immutable`.
+        unsafe impl $(<$($tyvar),*>)? $crate::Immutable for $name$(<$($tyvar),*>)?
+        where
+            $(
+                $($tuple_field_ty: $crate::Immutable,)*
+            )?
+
+            $(
+                $($field_ty: $crate::Immutable,)*
+            )?
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+    };
+    (@assert_allowed_struct_repr #[repr(transparent)]) => {};
+    (@assert_allowed_struct_repr #[repr(C)]) => {};
+    (@assert_allowed_struct_repr #[$_attr:meta]) => {
+        compile_error!("repr must be `#[repr(transparent)]` or `#[repr(C)]`");
+    };
+    (
+        @struct_padding_check #[repr(transparent)]
+        $(($($tuple_field_ty:ty),*))?
+        $({$($field_ty:ty),*})?
+    ) => {
+        // SAFETY: `#[repr(transparent)]` structs cannot have the same layout as
+        // their single non-zero-sized field, and so cannot have any padding
+        // outside of that field.
+        0
+    };
+    (
+        @struct_padding_check #[repr(C)]
+        $(($($tuple_field_ty:ty),*))?
+        $({$($field_ty:ty),*})?
+    ) => {
+        $crate::struct_padding!(
+            Self,
+            None,
+            None,
+            [
+                $($($tuple_field_ty),*)?
+                $($($field_ty),*)?
+            ]
+        )
+    };
+    (
+        #[repr(C)]
+        $(#[$attr:meta])*
+        $vis:vis union $name:ident {
+            $(
+                $field_name:ident: $field_ty:ty,
+            )*
+        }
+    ) => {
+        $(#[$attr])*
+        #[repr(C)]
+        $vis union $name {
+            $(
+                $field_name: $field_ty,
+            )*
+        }
+
+        // SAFETY: See inline.
+        unsafe impl $crate::TryFromBytes for $name
+        where
+            $(
+                $field_ty: $crate::FromBytes,
+            )*
+        {
+            #[inline(always)]
+            fn is_bit_valid<A>(_: $crate::Maybe<'_, Self, A>) -> bool
+            where
+                A: $crate::invariant::Alignment,
+            {
+                // SAFETY: This macro only accepts `#[repr(C)]` unions, and this
+                // `impl` block requires all field types to be `FromBytes`.
+                // Thus, all initialized byte sequences constitutes valid
+                // instances of `Self`.
+                true
+            }
+
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` unions, and this `impl`
+        // block requires all field types to be `FromBytes`, which is a
+        // sub-trait of `FromZeros`.
+        unsafe impl $crate::FromZeros for $name
+        where
+            $(
+                $field_ty: $crate::FromBytes,
+            )*
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` unions, and this `impl`
+        // block requires all field types to be `FromBytes`.
+        unsafe impl $crate::FromBytes for $name
+        where
+            $(
+                $field_ty: $crate::FromBytes,
+            )*
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` unions, this `impl`
+        // block requires all field types to be `IntoBytes`, and a padding check
+        // is used to ensures that there are no padding bytes before or after
+        // any field.
+        unsafe impl $crate::IntoBytes for $name
+        where
+            $(
+                $field_ty: $crate::IntoBytes,
+            )*
+            (): $crate::util::macro_util::PaddingFree<
+                Self,
+                {
+                    $crate::union_padding!(
+                        Self,
+                        None::<usize>,
+                        None::<usize>,
+                        [$($field_ty),*]
+                    )
+                },
+            >,
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+
+        // SAFETY: This macro only accepts `#[repr(C)]` unions, and this `impl`
+        // block requires all field types to be `Immutable`.
+        unsafe impl $crate::Immutable for $name
+        where
+            $(
+                $field_ty: $crate::Immutable,
+            )*
+        {
+            fn only_derive_is_allowed_to_implement_this_trait() {}
+        }
+    };
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        byteorder::native_endian::{U16, U32},
+        util::testutil::*,
+        *,
+    };
+
+    #[derive(KnownLayout, Immutable, FromBytes, IntoBytes, PartialEq, Debug)]
+    #[repr(C)]
+    struct SliceDst<T, U> {
+        a: T,
+        b: [U],
+    }
+
+    #[test]
+    fn test_transmute() {
+        // Test that memory is transmuted as expected.
+        let array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        let array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        let x: [[u8; 2]; 4] = transmute!(array_of_u8s);
+        assert_eq!(x, array_of_arrays);
+        let x: [u8; 8] = transmute!(array_of_arrays);
+        assert_eq!(x, array_of_u8s);
+
+        // Test that memory is transmuted as expected when shrinking.
+        let x: [[u8; 2]; 3] = transmute!(#![allow(shrink)] array_of_u8s);
+        assert_eq!(x, [[0u8, 1], [2, 3], [4, 5]]);
+
+        // Test that the source expression's value is forgotten rather than
+        // dropped.
+        #[derive(IntoBytes)]
+        #[repr(transparent)]
+        struct PanicOnDrop(());
+        impl Drop for PanicOnDrop {
+            fn drop(&mut self) {
+                panic!("PanicOnDrop::drop");
+            }
+        }
+        #[allow(clippy::let_unit_value)]
+        let _: () = transmute!(PanicOnDrop(()));
+        #[allow(clippy::let_unit_value)]
+        let _: () = transmute!(#![allow(shrink)] PanicOnDrop(()));
+
+        // Test that `transmute!` is legal in a const context.
+        const ARRAY_OF_U8S: [u8; 8] = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        const ARRAY_OF_ARRAYS: [[u8; 2]; 4] = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        const X: [[u8; 2]; 4] = transmute!(ARRAY_OF_U8S);
+        assert_eq!(X, ARRAY_OF_ARRAYS);
+        const X_SHRINK: [[u8; 2]; 3] = transmute!(#![allow(shrink)] ARRAY_OF_U8S);
+        assert_eq!(X_SHRINK, [[0u8, 1], [2, 3], [4, 5]]);
+
+        // Test that `transmute!` works with `!Immutable` types.
+        let x: usize = transmute!(UnsafeCell::new(1usize));
+        assert_eq!(x, 1);
+        let x: UnsafeCell<usize> = transmute!(1usize);
+        assert_eq!(x.into_inner(), 1);
+        let x: UnsafeCell<isize> = transmute!(UnsafeCell::new(1usize));
+        assert_eq!(x.into_inner(), 1);
+    }
+
+    // A `Sized` type which doesn't implement `KnownLayout` (it is "not
+    // `KnownLayout`", or `Nkl`).
+    //
+    // This permits us to test that `transmute_ref!` and `transmute_mut!` work
+    // for types which are `Sized + !KnownLayout`. When we added support for
+    // slice DSTs in #1924, this new support relied on `KnownLayout`, but we
+    // need to make sure to remain backwards-compatible with code which uses
+    // these macros with types which are `!KnownLayout`.
+    #[derive(FromBytes, IntoBytes, Immutable, PartialEq, Eq, Debug)]
+    #[repr(transparent)]
+    struct Nkl<T>(T);
+
+    #[test]
+    fn test_transmute_ref() {
+        // Test that memory is transmuted as expected.
+        let array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        let array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        let x: &[[u8; 2]; 4] = transmute_ref!(&array_of_u8s);
+        assert_eq!(*x, array_of_arrays);
+        let x: &[u8; 8] = transmute_ref!(&array_of_arrays);
+        assert_eq!(*x, array_of_u8s);
+
+        // Test that `transmute_ref!` is legal in a const context.
+        const ARRAY_OF_U8S: [u8; 8] = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        const ARRAY_OF_ARRAYS: [[u8; 2]; 4] = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        #[allow(clippy::redundant_static_lifetimes)]
+        const X: &'static [[u8; 2]; 4] = transmute_ref!(&ARRAY_OF_U8S);
+        assert_eq!(*X, ARRAY_OF_ARRAYS);
+
+        // Test sized -> unsized transmutation.
+        let array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        let array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        let slice_of_arrays = &array_of_arrays[..];
+        let x: &[[u8; 2]] = transmute_ref!(&array_of_u8s);
+        assert_eq!(x, slice_of_arrays);
+
+        // Before 1.61.0, we can't define the `const fn transmute_ref` function
+        // that we do on and after 1.61.0.
+        #[cfg(no_zerocopy_generic_bounds_in_const_fn_1_61_0)]
+        {
+            // Test that `transmute_ref!` supports non-`KnownLayout` `Sized`
+            // types.
+            const ARRAY_OF_NKL_U8S: Nkl<[u8; 8]> = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
+            const ARRAY_OF_NKL_ARRAYS: Nkl<[[u8; 2]; 4]> = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
+            const X_NKL: &Nkl<[[u8; 2]; 4]> = transmute_ref!(&ARRAY_OF_NKL_U8S);
+            assert_eq!(*X_NKL, ARRAY_OF_NKL_ARRAYS);
+        }
+
+        #[cfg(not(no_zerocopy_generic_bounds_in_const_fn_1_61_0))]
+        {
+            // Call through a generic function to make sure our autoref
+            // specialization trick works even when types are generic.
+            const fn transmute_ref<T, U>(t: &T) -> &U
+            where
+                T: IntoBytes + Immutable,
+                U: FromBytes + Immutable,
+            {
+                transmute_ref!(t)
+            }
+
+            // Test that `transmute_ref!` supports non-`KnownLayout` `Sized`
+            // types.
+            const ARRAY_OF_NKL_U8S: Nkl<[u8; 8]> = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
+            const ARRAY_OF_NKL_ARRAYS: Nkl<[[u8; 2]; 4]> = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
+            const X_NKL: &Nkl<[[u8; 2]; 4]> = transmute_ref(&ARRAY_OF_NKL_U8S);
+            assert_eq!(*X_NKL, ARRAY_OF_NKL_ARRAYS);
+        }
+
+        // Test that `transmute_ref!` works on slice DSTs in and that memory is
+        // transmuted as expected.
+        let slice_dst_of_u8s =
+            SliceDst::<U16, [u8; 2]>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
+        let slice_dst_of_u16s =
+            SliceDst::<U16, U16>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
+        let x: &SliceDst<U16, U16> = transmute_ref!(slice_dst_of_u8s);
+        assert_eq!(x, slice_dst_of_u16s);
+
+        let slice_dst_of_u8s =
+            SliceDst::<U16, u8>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
+        let x: &[u8] = transmute_ref!(slice_dst_of_u8s);
+        assert_eq!(x, [0, 1, 2, 3, 4, 5]);
+
+        let x: &[u8] = transmute_ref!(slice_dst_of_u16s);
+        assert_eq!(x, [0, 1, 2, 3, 4, 5]);
+
+        let x: &[U16] = transmute_ref!(slice_dst_of_u16s);
+        let slice_of_u16s: &[U16] = <[U16]>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
+        assert_eq!(x, slice_of_u16s);
+
+        // Test that transmuting from a type with larger trailing slice offset
+        // and larger trailing slice element works.
+        let bytes = &[0, 1, 2, 3, 4, 5, 6, 7][..];
+        let slice_dst_big = SliceDst::<U32, U16>::ref_from_bytes(bytes).unwrap();
+        let slice_dst_small = SliceDst::<U16, u8>::ref_from_bytes(bytes).unwrap();
+        let x: &SliceDst<U16, u8> = transmute_ref!(slice_dst_big);
+        assert_eq!(x, slice_dst_small);
+
+        // Test that it's legal to transmute a reference while shrinking the
+        // lifetime (note that `X` has the lifetime `'static`).
+        let x: &[u8; 8] = transmute_ref!(X);
+        assert_eq!(*x, ARRAY_OF_U8S);
+
+        // Test that `transmute_ref!` supports decreasing alignment.
+        let u = AU64(0);
+        let array = [0, 0, 0, 0, 0, 0, 0, 0];
+        let x: &[u8; 8] = transmute_ref!(&u);
+        assert_eq!(*x, array);
+
+        // Test that a mutable reference can be turned into an immutable one.
+        let mut x = 0u8;
+        #[allow(clippy::useless_transmute)]
+        let y: &u8 = transmute_ref!(&mut x);
+        assert_eq!(*y, 0);
+    }
+
+    #[test]
+    fn test_try_transmute() {
+        // Test that memory is transmuted with `try_transmute` as expected.
+        let array_of_bools = [false, true, false, true, false, true, false, true];
+        let array_of_arrays = [[0, 1], [0, 1], [0, 1], [0, 1]];
+        let x: Result<[[u8; 2]; 4], _> = try_transmute!(array_of_bools);
+        assert_eq!(x, Ok(array_of_arrays));
+        let x: Result<[bool; 8], _> = try_transmute!(array_of_arrays);
+        assert_eq!(x, Ok(array_of_bools));
+
+        // Test that `try_transmute!` works with `!Immutable` types.
+        let x: Result<usize, _> = try_transmute!(UnsafeCell::new(1usize));
+        assert_eq!(x.unwrap(), 1);
+        let x: Result<UnsafeCell<usize>, _> = try_transmute!(1usize);
+        assert_eq!(x.unwrap().into_inner(), 1);
+        let x: Result<UnsafeCell<isize>, _> = try_transmute!(UnsafeCell::new(1usize));
+        assert_eq!(x.unwrap().into_inner(), 1);
+
+        #[derive(FromBytes, IntoBytes, Debug, PartialEq)]
+        #[repr(transparent)]
+        struct PanicOnDrop<T>(T);
+
+        impl<T> Drop for PanicOnDrop<T> {
+            fn drop(&mut self) {
+                panic!("PanicOnDrop dropped");
+            }
+        }
+
+        // Since `try_transmute!` semantically moves its argument on failure,
+        // the `PanicOnDrop` is not dropped, and thus this shouldn't panic.
+        let x: Result<usize, _> = try_transmute!(PanicOnDrop(1usize));
+        assert_eq!(x, Ok(1));
+
+        // Since `try_transmute!` semantically returns ownership of its argument
+        // on failure, the `PanicOnDrop` is returned rather than dropped, and
+        // thus this shouldn't panic.
+        let y: Result<bool, _> = try_transmute!(PanicOnDrop(2u8));
+        // We have to use `map_err` instead of comparing against
+        // `Err(PanicOnDrop(2u8))` because the latter would create and then drop
+        // its `PanicOnDrop` temporary, which would cause a panic.
+        assert_eq!(y.as_ref().map_err(|p| &p.src.0), Err::<&bool, _>(&2u8));
+        mem::forget(y);
+    }
+
+    #[test]
+    fn test_try_transmute_ref() {
+        // Test that memory is transmuted with `try_transmute_ref` as expected.
+        let array_of_bools = &[false, true, false, true, false, true, false, true];
+        let array_of_arrays = &[[0, 1], [0, 1], [0, 1], [0, 1]];
+        let x: Result<&[[u8; 2]; 4], _> = try_transmute_ref!(array_of_bools);
+        assert_eq!(x, Ok(array_of_arrays));
+        let x: Result<&[bool; 8], _> = try_transmute_ref!(array_of_arrays);
+        assert_eq!(x, Ok(array_of_bools));
+
+        // Test that it's legal to transmute a reference while shrinking the
+        // lifetime.
+        {
+            let x: Result<&[[u8; 2]; 4], _> = try_transmute_ref!(array_of_bools);
+            assert_eq!(x, Ok(array_of_arrays));
+        }
+
+        // Test that `try_transmute_ref!` supports decreasing alignment.
+        let u = AU64(0);
+        let array = [0u8, 0, 0, 0, 0, 0, 0, 0];
+        let x: Result<&[u8; 8], _> = try_transmute_ref!(&u);
+        assert_eq!(x, Ok(&array));
+
+        // Test that a mutable reference can be turned into an immutable one.
+        let mut x = 0u8;
+        #[allow(clippy::useless_transmute)]
+        let y: Result<&u8, _> = try_transmute_ref!(&mut x);
+        assert_eq!(y, Ok(&0));
+
+        // Test that sized types work which don't implement `KnownLayout`.
+        let array_of_nkl_u8s = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
+        let array_of_nkl_arrays = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
+        let x: Result<&Nkl<[[u8; 2]; 4]>, _> = try_transmute_ref!(&array_of_nkl_u8s);
+        assert_eq!(x, Ok(&array_of_nkl_arrays));
+
+        // Test sized -> unsized transmutation.
+        let array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        let array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        let slice_of_arrays = &array_of_arrays[..];
+        let x: Result<&[[u8; 2]], _> = try_transmute_ref!(&array_of_u8s);
+        assert_eq!(x, Ok(slice_of_arrays));
+
+        // Test unsized -> unsized transmutation.
+        let slice_dst_of_u8s =
+            SliceDst::<U16, [u8; 2]>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
+        let slice_dst_of_u16s =
+            SliceDst::<U16, U16>::ref_from_bytes(&[0, 1, 2, 3, 4, 5][..]).unwrap();
+        let x: Result<&SliceDst<U16, U16>, _> = try_transmute_ref!(slice_dst_of_u8s);
+        assert_eq!(x, Ok(slice_dst_of_u16s));
+    }
+
+    #[test]
+    fn test_try_transmute_mut() {
+        // Test that memory is transmuted with `try_transmute_mut` as expected.
+        let array_of_u8s = &mut [0u8, 1, 0, 1, 0, 1, 0, 1];
+        let array_of_arrays = &mut [[0u8, 1], [0, 1], [0, 1], [0, 1]];
+        let x: Result<&mut [[u8; 2]; 4], _> = try_transmute_mut!(array_of_u8s);
+        assert_eq!(x, Ok(array_of_arrays));
+
+        let array_of_bools = &mut [false, true, false, true, false, true, false, true];
+        let array_of_arrays = &mut [[0u8, 1], [0, 1], [0, 1], [0, 1]];
+        let x: Result<&mut [bool; 8], _> = try_transmute_mut!(array_of_arrays);
+        assert_eq!(x, Ok(array_of_bools));
+
+        // Test that it's legal to transmute a reference while shrinking the
+        // lifetime.
+        let array_of_bools = &mut [false, true, false, true, false, true, false, true];
+        let array_of_arrays = &mut [[0u8, 1], [0, 1], [0, 1], [0, 1]];
+        {
+            let x: Result<&mut [bool; 8], _> = try_transmute_mut!(array_of_arrays);
+            assert_eq!(x, Ok(array_of_bools));
+        }
+
+        // Test that `try_transmute_mut!` supports decreasing alignment.
+        let u = &mut AU64(0);
+        let array = &mut [0u8, 0, 0, 0, 0, 0, 0, 0];
+        let x: Result<&mut [u8; 8], _> = try_transmute_mut!(u);
+        assert_eq!(x, Ok(array));
+
+        // Test that a mutable reference can be turned into an immutable one.
+        let mut x = 0u8;
+        #[allow(clippy::useless_transmute)]
+        let y: Result<&mut u8, _> = try_transmute_mut!(&mut x);
+        assert_eq!(y, Ok(&mut 0));
+
+        // Test that sized types work which don't implement `KnownLayout`.
+        let mut array_of_nkl_u8s = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
+        let mut array_of_nkl_arrays = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
+        let x: Result<&mut Nkl<[[u8; 2]; 4]>, _> = try_transmute_mut!(&mut array_of_nkl_u8s);
+        assert_eq!(x, Ok(&mut array_of_nkl_arrays));
+
+        // Test sized -> unsized transmutation.
+        let mut array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        let mut array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        let slice_of_arrays = &mut array_of_arrays[..];
+        let x: Result<&mut [[u8; 2]], _> = try_transmute_mut!(&mut array_of_u8s);
+        assert_eq!(x, Ok(slice_of_arrays));
+
+        // Test unsized -> unsized transmutation.
+        let mut bytes = [0, 1, 2, 3, 4, 5, 6];
+        let slice_dst_of_u8s = SliceDst::<u8, [u8; 2]>::mut_from_bytes(&mut bytes[..]).unwrap();
+        let mut bytes = [0, 1, 2, 3, 4, 5, 6];
+        let slice_dst_of_u16s = SliceDst::<u8, U16>::mut_from_bytes(&mut bytes[..]).unwrap();
+        let x: Result<&mut SliceDst<u8, U16>, _> = try_transmute_mut!(slice_dst_of_u8s);
+        assert_eq!(x, Ok(slice_dst_of_u16s));
+    }
+
+    #[test]
+    fn test_transmute_mut() {
+        // Test that memory is transmuted as expected.
+        let mut array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        let mut array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        let x: &mut [[u8; 2]; 4] = transmute_mut!(&mut array_of_u8s);
+        assert_eq!(*x, array_of_arrays);
+        let x: &mut [u8; 8] = transmute_mut!(&mut array_of_arrays);
+        assert_eq!(*x, array_of_u8s);
+
+        {
+            // Test that it's legal to transmute a reference while shrinking the
+            // lifetime.
+            let x: &mut [u8; 8] = transmute_mut!(&mut array_of_arrays);
+            assert_eq!(*x, array_of_u8s);
+        }
+
+        // Test that `transmute_mut!` supports non-`KnownLayout` types.
+        let mut array_of_u8s = Nkl([0u8, 1, 2, 3, 4, 5, 6, 7]);
+        let mut array_of_arrays = Nkl([[0, 1], [2, 3], [4, 5], [6, 7]]);
+        let x: &mut Nkl<[[u8; 2]; 4]> = transmute_mut!(&mut array_of_u8s);
+        assert_eq!(*x, array_of_arrays);
+        let x: &mut Nkl<[u8; 8]> = transmute_mut!(&mut array_of_arrays);
+        assert_eq!(*x, array_of_u8s);
+
+        // Test that `transmute_mut!` supports decreasing alignment.
+        let mut u = AU64(0);
+        let array = [0, 0, 0, 0, 0, 0, 0, 0];
+        let x: &[u8; 8] = transmute_mut!(&mut u);
+        assert_eq!(*x, array);
+
+        // Test that a mutable reference can be turned into an immutable one.
+        let mut x = 0u8;
+        #[allow(clippy::useless_transmute)]
+        let y: &u8 = transmute_mut!(&mut x);
+        assert_eq!(*y, 0);
+
+        // Test that `transmute_mut!` works on slice DSTs in and that memory is
+        // transmuted as expected.
+        let mut bytes = [0, 1, 2, 3, 4, 5, 6];
+        let slice_dst_of_u8s = SliceDst::<u8, [u8; 2]>::mut_from_bytes(&mut bytes[..]).unwrap();
+        let mut bytes = [0, 1, 2, 3, 4, 5, 6];
+        let slice_dst_of_u16s = SliceDst::<u8, U16>::mut_from_bytes(&mut bytes[..]).unwrap();
+        let x: &mut SliceDst<u8, U16> = transmute_mut!(slice_dst_of_u8s);
+        assert_eq!(x, slice_dst_of_u16s);
+
+        // Test that `transmute_mut!` works on slices that memory is transmuted
+        // as expected.
+        let array_of_u16s: &mut [u16] = &mut [0u16, 1, 2];
+        let array_of_i16s: &mut [i16] = &mut [0i16, 1, 2];
+        let x: &mut [i16] = transmute_mut!(array_of_u16s);
+        assert_eq!(x, array_of_i16s);
+
+        // Test that transmuting from a type with larger trailing slice offset
+        // and larger trailing slice element works.
+        let mut bytes = [0, 1, 2, 3, 4, 5, 6, 7];
+        let slice_dst_big = SliceDst::<U32, U16>::mut_from_bytes(&mut bytes[..]).unwrap();
+        let mut bytes = [0, 1, 2, 3, 4, 5, 6, 7];
+        let slice_dst_small = SliceDst::<U16, u8>::mut_from_bytes(&mut bytes[..]).unwrap();
+        let x: &mut SliceDst<U16, u8> = transmute_mut!(slice_dst_big);
+        assert_eq!(x, slice_dst_small);
+
+        // Test sized -> unsized transmutation.
+        let mut array_of_u8s = [0u8, 1, 2, 3, 4, 5, 6, 7];
+        let mut array_of_arrays = [[0, 1], [2, 3], [4, 5], [6, 7]];
+        let slice_of_arrays = &mut array_of_arrays[..];
+        let x: &mut [[u8; 2]] = transmute_mut!(&mut array_of_u8s);
+        assert_eq!(x, slice_of_arrays);
+    }
+
+    #[test]
+    fn test_macros_evaluate_args_once() {
+        let mut ctr = 0;
+        #[allow(clippy::useless_transmute)]
+        let _: usize = transmute!({
+            ctr += 1;
+            0usize
+        });
+        assert_eq!(ctr, 1);
+
+        let mut ctr = 0;
+        let _: &usize = transmute_ref!({
+            ctr += 1;
+            &0usize
+        });
+        assert_eq!(ctr, 1);
+
+        let mut ctr: usize = 0;
+        let _: &mut usize = transmute_mut!({
+            ctr += 1;
+            &mut ctr
+        });
+        assert_eq!(ctr, 1);
+
+        let mut ctr = 0;
+        #[allow(clippy::useless_transmute)]
+        let _: usize = try_transmute!({
+            ctr += 1;
+            0usize
+        })
+        .unwrap();
+        assert_eq!(ctr, 1);
+    }
+
+    #[test]
+    fn test_include_value() {
+        const AS_U32: u32 = include_value!("../testdata/include_value/data");
+        assert_eq!(AS_U32, u32::from_ne_bytes([b'a', b'b', b'c', b'd']));
+        const AS_I32: i32 = include_value!("../testdata/include_value/data");
+        assert_eq!(AS_I32, i32::from_ne_bytes([b'a', b'b', b'c', b'd']));
+    }
+
+    #[test]
+    #[allow(non_camel_case_types, unreachable_pub, dead_code)]
+    fn test_cryptocorrosion_derive_traits() {
+        // Test the set of invocations added in
+        // https://github.com/cryptocorrosion/cryptocorrosion/pull/85
+
+        fn assert_impls<T: FromBytes + IntoBytes + Immutable>() {}
+
+        cryptocorrosion_derive_traits! {
+            #[repr(C)]
+            #[derive(Clone, Copy)]
+            pub union vec128_storage {
+                d: [u32; 4],
+                q: [u64; 2],
+            }
+        }
+
+        assert_impls::<vec128_storage>();
+
+        cryptocorrosion_derive_traits! {
+            #[repr(transparent)]
+            #[derive(Copy, Clone, Debug, PartialEq)]
+            pub struct u32x4_generic([u32; 4]);
+        }
+
+        assert_impls::<u32x4_generic>();
+
+        cryptocorrosion_derive_traits! {
+            #[repr(transparent)]
+            #[derive(Copy, Clone, Debug, PartialEq)]
+            pub struct u64x2_generic([u64; 2]);
+        }
+
+        assert_impls::<u64x2_generic>();
+
+        cryptocorrosion_derive_traits! {
+            #[repr(transparent)]
+            #[derive(Copy, Clone, Debug, PartialEq)]
+            pub struct u128x1_generic([u128; 1]);
+        }
+
+        assert_impls::<u128x1_generic>();
+
+        cryptocorrosion_derive_traits! {
+            #[repr(transparent)]
+            #[derive(Copy, Clone, Default)]
+            #[allow(non_camel_case_types)]
+            pub struct x2<W, G>(pub [W; 2], PhantomData<G>);
+        }
+
+        enum NotZerocopy {}
+        assert_impls::<x2<(), NotZerocopy>>();
+
+        cryptocorrosion_derive_traits! {
+            #[repr(transparent)]
+            #[derive(Copy, Clone, Default)]
+            #[allow(non_camel_case_types)]
+            pub struct x4<W>(pub [W; 4]);
+        }
+
+        assert_impls::<x4<()>>();
+
+        #[cfg(feature = "simd")]
+        #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+        {
+            #[cfg(target_arch = "x86")]
+            use core::arch::x86::{__m128i, __m256i};
+            #[cfg(target_arch = "x86_64")]
+            use core::arch::x86_64::{__m128i, __m256i};
+
+            cryptocorrosion_derive_traits! {
+                #[repr(C)]
+                #[derive(Copy, Clone)]
+                pub struct X4(__m128i, __m128i, __m128i, __m128i);
+            }
+
+            assert_impls::<X4>();
+
+            cryptocorrosion_derive_traits! {
+                #[repr(C)]
+                /// Generic wrapper for unparameterized storage of any of the
+                /// possible impls. Converting into and out of this type should
+                /// be essentially free, although it may be more aligned than a
+                /// particular impl requires.
+                #[allow(non_camel_case_types)]
+                #[derive(Copy, Clone)]
+                pub union vec128_storage {
+                    u32x4: [u32; 4],
+                    u64x2: [u64; 2],
+                    u128x1: [u128; 1],
+                    sse2: __m128i,
+                }
+            }
+
+            assert_impls::<vec128_storage>();
+
+            cryptocorrosion_derive_traits! {
+                #[repr(transparent)]
+                #[allow(non_camel_case_types)]
+                #[derive(Copy, Clone)]
+                pub struct vec<S3, S4, NI> {
+                    x: __m128i,
+                    s3: PhantomData<S3>,
+                    s4: PhantomData<S4>,
+                    ni: PhantomData<NI>,
+                }
+            }
+
+            assert_impls::<vec<NotZerocopy, NotZerocopy, NotZerocopy>>();
+
+            cryptocorrosion_derive_traits! {
+                #[repr(transparent)]
+                #[derive(Copy, Clone)]
+                pub struct u32x4x2_avx2<NI> {
+                    x: __m256i,
+                    ni: PhantomData<NI>,
+                }
+            }
+
+            assert_impls::<u32x4x2_avx2<NotZerocopy>>();
+        }
+
+        // Make sure that our derive works for `#[repr(C)]` structs even though
+        // cryptocorrosion doesn't currently have any.
+        cryptocorrosion_derive_traits! {
+            #[repr(C)]
+            #[derive(Copy, Clone, Debug, PartialEq)]
+            pub struct ReprC(u8, u8, u16);
+        }
+    }
+}