1// Copyright 2022 The Fuchsia Authors
2//
3// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
4// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
5// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
6// This file may not be copied, modified, or distributed except according to
7// those terms.
8
9//! Utilities used by macros and by `zerocopy-derive`.
10//!
11//! These are defined here `zerocopy` rather than in code generated by macros or
12//! by `zerocopy-derive` so that they can be compiled once rather than
13//! recompiled for every invocation (e.g., if they were defined in generated
14//! code, then deriving `AsBytes` and `FromBytes` on three different types would
15//! result in the code in question being emitted and compiled six different
16//! times).
17
18#![allow(missing_debug_implementations)]
19
20use core::{marker::PhantomData, mem::ManuallyDrop};
21
22// TODO(#29), TODO(https://github.com/rust-lang/rust/issues/69835): Remove this
23// `cfg` when `size_of_val_raw` is stabilized.
24#[cfg(__INTERNAL_USE_ONLY_NIGHLTY_FEATURES_IN_TESTS)]
25use core::ptr::{self, NonNull};
26
27/// A compile-time check that should be one particular value.
28pub trait ShouldBe<const VALUE: bool> {}
29
30/// A struct for checking whether `T` contains padding.
31pub struct HasPadding<T: ?Sized, const VALUE: bool>(PhantomData<T>);
32
33impl<T: ?Sized, const VALUE: bool> ShouldBe<VALUE> for HasPadding<T, VALUE> {}
34
35/// A type whose size is equal to `align_of::<T>()`.
36#[repr(C)]
37pub struct AlignOf<T> {
38 // This field ensures that:
39 // - The size is always at least 1 (the minimum possible alignment).
40 // - If the alignment is greater than 1, Rust has to round up to the next
41 // multiple of it in order to make sure that `Align`'s size is a multiple
42 // of that alignment. Without this field, its size could be 0, which is a
43 // valid multiple of any alignment.
44 _u: u8,
45 _a: [T; 0],
46}
47
48impl<T> AlignOf<T> {
49 #[inline(never)] // Make `missing_inline_in_public_items` happy.
50 pub fn into_t(self) -> T {
51 unreachable!()
52 }
53}
54
55/// A type whose size is equal to `max(align_of::<T>(), align_of::<U>())`.
56#[repr(C)]
57pub union MaxAlignsOf<T, U> {
58 _t: ManuallyDrop<AlignOf<T>>,
59 _u: ManuallyDrop<AlignOf<U>>,
60}
61
62impl<T, U> MaxAlignsOf<T, U> {
63 #[inline(never)] // Make `missing_inline_in_public_items` happy.
64 pub fn new(_t: T, _u: U) -> MaxAlignsOf<T, U> {
65 unreachable!()
66 }
67}
68
69const _64K: usize = 1 << 16;
70
71// TODO(#29), TODO(https://github.com/rust-lang/rust/issues/69835): Remove this
72// `cfg` when `size_of_val_raw` is stabilized.
73#[cfg(__INTERNAL_USE_ONLY_NIGHLTY_FEATURES_IN_TESTS)]
74#[repr(C, align(65536))]
75struct Aligned64kAllocation([u8; _64K]);
76
77/// A pointer to an aligned allocation of size 2^16.
78///
79/// # Safety
80///
81/// `ALIGNED_64K_ALLOCATION` is guaranteed to point to the entirety of an
82/// allocation with size and alignment 2^16, and to have valid provenance.
83// TODO(#29), TODO(https://github.com/rust-lang/rust/issues/69835): Remove this
84// `cfg` when `size_of_val_raw` is stabilized.
85#[cfg(__INTERNAL_USE_ONLY_NIGHLTY_FEATURES_IN_TESTS)]
86pub const ALIGNED_64K_ALLOCATION: NonNull<[u8]> = {
87 const REF: &Aligned64kAllocation = &Aligned64kAllocation([0; _64K]);
88 let ptr: *const Aligned64kAllocation = REF;
89 let ptr: *const [u8] = ptr::slice_from_raw_parts(ptr.cast(), _64K);
90 // SAFETY:
91 // - `ptr` is derived from a Rust reference, which is guaranteed to be
92 // non-null.
93 // - `ptr` is derived from an `&Aligned64kAllocation`, which has size and
94 // alignment `_64K` as promised. Its length is initialized to `_64K`,
95 // which means that it refers to the entire allocation.
96 // - `ptr` is derived from a Rust reference, which is guaranteed to have
97 // valid provenance.
98 //
99 // TODO(#429): Once `NonNull::new_unchecked` docs document that it preserves
100 // provenance, cite those docs.
101 // TODO: Replace this `as` with `ptr.cast_mut()` once our MSRV >= 1.65
102 #[allow(clippy::as_conversions)]
103 unsafe {
104 NonNull::new_unchecked(ptr as *mut _)
105 }
106};
107
108/// Computes the offset of the base of the field `$trailing_field_name` within
109/// the type `$ty`.
110///
111/// `trailing_field_offset!` produces code which is valid in a `const` context.
112// TODO(#29), TODO(https://github.com/rust-lang/rust/issues/69835): Remove this
113// `cfg` when `size_of_val_raw` is stabilized.
114#[cfg(__INTERNAL_USE_ONLY_NIGHLTY_FEATURES_IN_TESTS)]
115#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
116#[macro_export]
117macro_rules! trailing_field_offset {
118 ($ty:ty, $trailing_field_name:tt) => {{
119 let min_size = {
120 let zero_elems: *const [()] =
121 $crate::macro_util::core_reexport::ptr::slice_from_raw_parts(
122 $crate::macro_util::core_reexport::ptr::NonNull::<()>::dangling()
123 .as_ptr()
124 .cast_const(),
125 0,
126 );
127 // SAFETY:
128 // - If `$ty` is `Sized`, `size_of_val_raw` is always safe to call.
129 // - Otherwise:
130 // - If `$ty` is not a slice DST, this pointer conversion will
131 // fail due to "mismatched vtable kinds", and compilation will
132 // fail.
133 // - If `$ty` is a slice DST, the safety requirement is that "the
134 // length of the slice tail must be an initialized integer, and
135 // the size of the entire value (dynamic tail length +
136 // statically sized prefix) must fit in isize." The length is
137 // initialized to 0 above, and Rust guarantees that no type's
138 // minimum size may overflow `isize`. [1]
139 //
140 // [1] TODO(#429),
141 // TODO(https://github.com/rust-lang/unsafe-code-guidelines/issues/465#issuecomment-1782206516):
142 // Citation for this?
143 unsafe {
144 #[allow(clippy::as_conversions)]
145 $crate::macro_util::core_reexport::mem::size_of_val_raw(zero_elems as *const $ty)
146 }
147 };
148
149 assert!(min_size <= _64K);
150
151 #[allow(clippy::as_conversions)]
152 let ptr = ALIGNED_64K_ALLOCATION.as_ptr() as *const $ty;
153
154 // SAFETY:
155 // - Thanks to the preceding `assert!`, we know that the value with zero
156 // elements fits in `_64K` bytes, and thus in the allocation addressed
157 // by `ALIGNED_64K_ALLOCATION`. The offset of the trailing field is
158 // guaranteed to be no larger than this size, so this field projection
159 // is guaranteed to remain in-bounds of its allocation.
160 // - Because the minimum size is no larger than `_64K` bytes, and
161 // because an object's size must always be a multiple of its alignment
162 // [1], we know that `$ty`'s alignment is no larger than `_64K`. The
163 // allocation addressed by `ALIGNED_64K_ALLOCATION` is guaranteed to
164 // be aligned to `_64K`, so `ptr` is guaranteed to satisfy `$ty`'s
165 // alignment.
166 //
167 // Note that, as of [2], this requirement is technically unnecessary
168 // for Rust versions >= 1.75.0, but no harm in guaranteeing it anyway
169 // until we bump our MSRV.
170 //
171 // [1] Per https://doc.rust-lang.org/reference/type-layout.html:
172 //
173 // The size of a value is always a multiple of its alignment.
174 //
175 // [2] https://github.com/rust-lang/reference/pull/1387
176 let field = unsafe {
177 $crate::macro_util::core_reexport::ptr::addr_of!((*ptr).$trailing_field_name)
178 };
179 // SAFETY:
180 // - Both `ptr` and `field` are derived from the same allocated object.
181 // - By the preceding safety comment, `field` is in bounds of that
182 // allocated object.
183 // - The distance, in bytes, between `ptr` and `field` is required to be
184 // a multiple of the size of `u8`, which is trivially true because
185 // `u8`'s size is 1.
186 // - The distance, in bytes, cannot overflow `isize`. This is guaranteed
187 // because no allocated object can have a size larger than can fit in
188 // `isize`. [1]
189 // - The distance being in-bounds cannot rely on wrapping around the
190 // address space. This is guaranteed because the same is guaranteed of
191 // allocated objects. [1]
192 //
193 // [1] TODO(#429), TODO(https://github.com/rust-lang/rust/pull/116675):
194 // Once these are guaranteed in the Reference, cite it.
195 let offset = unsafe { field.cast::<u8>().offset_from(ptr.cast::<u8>()) };
196 // Guaranteed not to be lossy: `field` comes after `ptr`, so the offset
197 // from `ptr` to `field` is guaranteed to be positive.
198 assert!(offset >= 0);
199 Some(
200 #[allow(clippy::as_conversions)]
201 {
202 offset as usize
203 },
204 )
205 }};
206}
207
208/// Computes alignment of `$ty: ?Sized`.
209///
210/// `align_of!` produces code which is valid in a `const` context.
211// TODO(#29), TODO(https://github.com/rust-lang/rust/issues/69835): Remove this
212// `cfg` when `size_of_val_raw` is stabilized.
213#[cfg(__INTERNAL_USE_ONLY_NIGHLTY_FEATURES_IN_TESTS)]
214#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
215#[macro_export]
216macro_rules! align_of {
217 ($ty:ty) => {{
218 // SAFETY: `OffsetOfTrailingIsAlignment` is `repr(C)`, and its layout is
219 // guaranteed [1] to begin with the single-byte layout for `_byte`,
220 // followed by the padding needed to align `_trailing`, then the layout
221 // for `_trailing`, and finally any trailing padding bytes needed to
222 // correctly-align the entire struct.
223 //
224 // This macro computes the alignment of `$ty` by counting the number of
225 // bytes preceeding `_trailing`. For instance, if the alignment of `$ty`
226 // is `1`, then no padding is required align `_trailing` and it will be
227 // located immediately after `_byte` at offset 1. If the alignment of
228 // `$ty` is 2, then a single padding byte is required before
229 // `_trailing`, and `_trailing` will be located at offset 2.
230
231 // This correspondence between offset and alignment holds for all valid
232 // Rust alignments, and we confirm this exhaustively (or, at least up to
233 // the maximum alignment supported by `trailing_field_offset!`) in
234 // `test_align_of_dst`.
235 //
236 // [1]: https://doc.rust-lang.org/nomicon/other-reprs.html#reprc
237
238 #[repr(C)]
239 struct OffsetOfTrailingIsAlignment {
240 _byte: u8,
241 _trailing: $ty,
242 }
243
244 trailing_field_offset!(OffsetOfTrailingIsAlignment, _trailing)
245 }};
246}
247
248/// Does the struct type `$t` have padding?
249///
250/// `$ts` is the list of the type of every field in `$t`. `$t` must be a
251/// struct type, or else `struct_has_padding!`'s result may be meaningless.
252///
253/// Note that `struct_has_padding!`'s results are independent of `repr` since
254/// they only consider the size of the type and the sizes of the fields.
255/// Whatever the repr, the size of the type already takes into account any
256/// padding that the compiler has decided to add. Structs with well-defined
257/// representations (such as `repr(C)`) can use this macro to check for padding.
258/// Note that while this may yield some consistent value for some `repr(Rust)`
259/// structs, it is not guaranteed across platforms or compilations.
260#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
261#[macro_export]
262macro_rules! struct_has_padding {
263 ($t:ty, $($ts:ty),*) => {
264 core::mem::size_of::<$t>() > 0 $(+ core::mem::size_of::<$ts>())*
265 };
266}
267
268/// Does the union type `$t` have padding?
269///
270/// `$ts` is the list of the type of every field in `$t`. `$t` must be a
271/// union type, or else `union_has_padding!`'s result may be meaningless.
272///
273/// Note that `union_has_padding!`'s results are independent of `repr` since
274/// they only consider the size of the type and the sizes of the fields.
275/// Whatever the repr, the size of the type already takes into account any
276/// padding that the compiler has decided to add. Unions with well-defined
277/// representations (such as `repr(C)`) can use this macro to check for padding.
278/// Note that while this may yield some consistent value for some `repr(Rust)`
279/// unions, it is not guaranteed across platforms or compilations.
280#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
281#[macro_export]
282macro_rules! union_has_padding {
283 ($t:ty, $($ts:ty),*) => {
284 false $(|| core::mem::size_of::<$t>() != core::mem::size_of::<$ts>())*
285 };
286}
287
288/// Does `t` have alignment greater than or equal to `u`? If not, this macro
289/// produces a compile error. It must be invoked in a dead codepath. This is
290/// used in `transmute_ref!` and `transmute_mut!`.
291#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
292#[macro_export]
293macro_rules! assert_align_gt_eq {
294 ($t:ident, $u: ident) => {{
295 // The comments here should be read in the context of this macro's
296 // invocations in `transmute_ref!` and `transmute_mut!`.
297 #[allow(clippy::missing_transmute_annotations)]
298 if false {
299 // The type wildcard in this bound is inferred to be `T` because
300 // `align_of.into_t()` is assigned to `t` (which has type `T`).
301 let align_of: $crate::macro_util::AlignOf<_> = unreachable!();
302 $t = align_of.into_t();
303 // `max_aligns` is inferred to have type `MaxAlignsOf<T, U>` because
304 // of the inferred types of `t` and `u`.
305 let mut max_aligns = $crate::macro_util::MaxAlignsOf::new($t, $u);
306
307 // This transmute will only compile successfully if
308 // `align_of::<T>() == max(align_of::<T>(), align_of::<U>())` - in
309 // other words, if `align_of::<T>() >= align_of::<U>()`.
310 //
311 // SAFETY: This code is never run.
312 max_aligns = unsafe { $crate::macro_util::core_reexport::mem::transmute(align_of) };
313 } else {
314 loop {}
315 }
316 }};
317}
318
319/// Do `t` and `u` have the same size? If not, this macro produces a compile
320/// error. It must be invoked in a dead codepath. This is used in
321/// `transmute_ref!` and `transmute_mut!`.
322#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
323#[macro_export]
324macro_rules! assert_size_eq {
325 ($t:ident, $u: ident) => {{
326 // The comments here should be read in the context of this macro's
327 // invocations in `transmute_ref!` and `transmute_mut!`.
328 if false {
329 // SAFETY: This code is never run.
330 $u = unsafe {
331 // Clippy: It's okay to transmute a type to itself.
332 #[allow(clippy::useless_transmute, clippy::missing_transmute_annotations)]
333 $crate::macro_util::core_reexport::mem::transmute($t)
334 };
335 } else {
336 loop {}
337 }
338 }};
339}
340
341/// Transmutes a reference of one type to a reference of another type.
342///
343/// # Safety
344///
345/// The caller must guarantee that:
346/// - `Src: AsBytes`
347/// - `Dst: FromBytes`
348/// - `size_of::<Src>() == size_of::<Dst>()`
349/// - `align_of::<Src>() >= align_of::<Dst>()`
350#[inline(always)]
351pub const unsafe fn transmute_ref<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
352 src: &'src Src,
353) -> &'dst Dst {
354 let src: *const Src = src;
355 let dst: *const Dst = src.cast::<Dst>();
356 // SAFETY:
357 // - We know that it is sound to view the target type of the input reference
358 // (`Src`) as the target type of the output reference (`Dst`) because the
359 // caller has guaranteed that `Src: AsBytes`, `Dst: FromBytes`, and
360 // `size_of::<Src>() == size_of::<Dst>()`.
361 // - We know that there are no `UnsafeCell`s, and thus we don't have to
362 // worry about `UnsafeCell` overlap, because `Src: AsBytes` and `Dst:
363 // FromBytes` both forbid `UnsafeCell`s.
364 // - The caller has guaranteed that alignment is not increased.
365 // - We know that the returned lifetime will not outlive the input lifetime
366 // thanks to the lifetime bounds on this function.
367 unsafe { &*dst }
368}
369
370/// Transmutes a mutable reference of one type to a mutable reference of another
371/// type.
372///
373/// # Safety
374///
375/// The caller must guarantee that:
376/// - `Src: FromBytes + AsBytes`
377/// - `Dst: FromBytes + AsBytes`
378/// - `size_of::<Src>() == size_of::<Dst>()`
379/// - `align_of::<Src>() >= align_of::<Dst>()`
380#[inline(always)]
381pub unsafe fn transmute_mut<'dst, 'src: 'dst, Src: 'src, Dst: 'dst>(
382 src: &'src mut Src,
383) -> &'dst mut Dst {
384 let src: *mut Src = src;
385 let dst: *mut Dst = src.cast::<Dst>();
386 // SAFETY:
387 // - We know that it is sound to view the target type of the input reference
388 // (`Src`) as the target type of the output reference (`Dst`) and
389 // vice-versa because the caller has guaranteed that `Src: FromBytes +
390 // AsBytes`, `Dst: FromBytes + AsBytes`, and `size_of::<Src>() ==
391 // size_of::<Dst>()`.
392 // - We know that there are no `UnsafeCell`s, and thus we don't have to
393 // worry about `UnsafeCell` overlap, because `Src: FromBytes + AsBytes`
394 // and `Dst: FromBytes + AsBytes` forbid `UnsafeCell`s.
395 // - The caller has guaranteed that alignment is not increased.
396 // - We know that the returned lifetime will not outlive the input lifetime
397 // thanks to the lifetime bounds on this function.
398 unsafe { &mut *dst }
399}
400
401// NOTE: We can't change this to a `pub use core as core_reexport` until [1] is
402// fixed or we update to a semver-breaking version (as of this writing, 0.8.0)
403// on the `main` branch.
404//
405// [1] https://github.com/obi1kenobi/cargo-semver-checks/issues/573
406pub mod core_reexport {
407 pub use core::*;
408
409 pub mod mem {
410 pub use core::mem::*;
411 }
412}
413
414#[cfg(test)]
415mod tests {
416 use core::mem;
417
418 use super::*;
419 use crate::util::testutil::*;
420
421 #[test]
422 fn test_align_of() {
423 macro_rules! test {
424 ($ty:ty) => {
425 assert_eq!(mem::size_of::<AlignOf<$ty>>(), mem::align_of::<$ty>());
426 };
427 }
428
429 test!(());
430 test!(u8);
431 test!(AU64);
432 test!([AU64; 2]);
433 }
434
435 #[test]
436 fn test_max_aligns_of() {
437 macro_rules! test {
438 ($t:ty, $u:ty) => {
439 assert_eq!(
440 mem::size_of::<MaxAlignsOf<$t, $u>>(),
441 core::cmp::max(mem::align_of::<$t>(), mem::align_of::<$u>())
442 );
443 };
444 }
445
446 test!(u8, u8);
447 test!(u8, AU64);
448 test!(AU64, u8);
449 }
450
451 #[test]
452 fn test_typed_align_check() {
453 // Test that the type-based alignment check used in
454 // `assert_align_gt_eq!` behaves as expected.
455
456 macro_rules! assert_t_align_gteq_u_align {
457 ($t:ty, $u:ty, $gteq:expr) => {
458 assert_eq!(
459 mem::size_of::<MaxAlignsOf<$t, $u>>() == mem::size_of::<AlignOf<$t>>(),
460 $gteq
461 );
462 };
463 }
464
465 assert_t_align_gteq_u_align!(u8, u8, true);
466 assert_t_align_gteq_u_align!(AU64, AU64, true);
467 assert_t_align_gteq_u_align!(AU64, u8, true);
468 assert_t_align_gteq_u_align!(u8, AU64, false);
469 }
470
471 // TODO(#29), TODO(https://github.com/rust-lang/rust/issues/69835): Remove
472 // this `cfg` when `size_of_val_raw` is stabilized.
473 #[allow(clippy::decimal_literal_representation)]
474 #[cfg(__INTERNAL_USE_ONLY_NIGHLTY_FEATURES_IN_TESTS)]
475 #[test]
476 fn test_trailing_field_offset() {
477 assert_eq!(mem::align_of::<Aligned64kAllocation>(), _64K);
478
479 macro_rules! test {
480 (#[$cfg:meta] ($($ts:ty),* ; $trailing_field_ty:ty) => $expect:expr) => {{
481 #[$cfg]
482 #[allow(dead_code)] // fields are never read
483 struct Test($($ts,)* $trailing_field_ty);
484 assert_eq!(test!(@offset $($ts),* ; $trailing_field_ty), $expect);
485 }};
486 (#[$cfg:meta] $(#[$cfgs:meta])* ($($ts:ty),* ; $trailing_field_ty:ty) => $expect:expr) => {
487 test!(#[$cfg] ($($ts),* ; $trailing_field_ty) => $expect);
488 test!($(#[$cfgs])* ($($ts),* ; $trailing_field_ty) => $expect);
489 };
490 (@offset ; $_trailing:ty) => { trailing_field_offset!(Test, 0) };
491 (@offset $_t:ty ; $_trailing:ty) => { trailing_field_offset!(Test, 1) };
492 }
493
494 test!(#[repr(C)] #[repr(transparent)] #[repr(packed)](; u8) => Some(0));
495 test!(#[repr(C)] #[repr(transparent)] #[repr(packed)](; [u8]) => Some(0));
496 test!(#[repr(C)] #[repr(C, packed)] (u8; u8) => Some(1));
497 test!(#[repr(C)] (; AU64) => Some(0));
498 test!(#[repr(C)] (; [AU64]) => Some(0));
499 test!(#[repr(C)] (u8; AU64) => Some(8));
500 test!(#[repr(C)] (u8; [AU64]) => Some(8));
501 test!(#[repr(C)] (; Nested<u8, AU64>) => Some(0));
502 test!(#[repr(C)] (; Nested<u8, [AU64]>) => Some(0));
503 test!(#[repr(C)] (u8; Nested<u8, AU64>) => Some(8));
504 test!(#[repr(C)] (u8; Nested<u8, [AU64]>) => Some(8));
505
506 // Test that `packed(N)` limits the offset of the trailing field.
507 test!(#[repr(C, packed( 1))] (u8; elain::Align< 2>) => Some( 1));
508 test!(#[repr(C, packed( 2))] (u8; elain::Align< 4>) => Some( 2));
509 test!(#[repr(C, packed( 4))] (u8; elain::Align< 8>) => Some( 4));
510 test!(#[repr(C, packed( 8))] (u8; elain::Align< 16>) => Some( 8));
511 test!(#[repr(C, packed( 16))] (u8; elain::Align< 32>) => Some( 16));
512 test!(#[repr(C, packed( 32))] (u8; elain::Align< 64>) => Some( 32));
513 test!(#[repr(C, packed( 64))] (u8; elain::Align< 128>) => Some( 64));
514 test!(#[repr(C, packed( 128))] (u8; elain::Align< 256>) => Some( 128));
515 test!(#[repr(C, packed( 256))] (u8; elain::Align< 512>) => Some( 256));
516 test!(#[repr(C, packed( 512))] (u8; elain::Align< 1024>) => Some( 512));
517 test!(#[repr(C, packed( 1024))] (u8; elain::Align< 2048>) => Some( 1024));
518 test!(#[repr(C, packed( 2048))] (u8; elain::Align< 4096>) => Some( 2048));
519 test!(#[repr(C, packed( 4096))] (u8; elain::Align< 8192>) => Some( 4096));
520 test!(#[repr(C, packed( 8192))] (u8; elain::Align< 16384>) => Some( 8192));
521 test!(#[repr(C, packed( 16384))] (u8; elain::Align< 32768>) => Some( 16384));
522 test!(#[repr(C, packed( 32768))] (u8; elain::Align< 65536>) => Some( 32768));
523 test!(#[repr(C, packed( 65536))] (u8; elain::Align< 131072>) => Some( 65536));
524 /* Alignments above 65536 are not yet supported.
525 test!(#[repr(C, packed( 131072))] (u8; elain::Align< 262144>) => Some( 131072));
526 test!(#[repr(C, packed( 262144))] (u8; elain::Align< 524288>) => Some( 262144));
527 test!(#[repr(C, packed( 524288))] (u8; elain::Align< 1048576>) => Some( 524288));
528 test!(#[repr(C, packed( 1048576))] (u8; elain::Align< 2097152>) => Some( 1048576));
529 test!(#[repr(C, packed( 2097152))] (u8; elain::Align< 4194304>) => Some( 2097152));
530 test!(#[repr(C, packed( 4194304))] (u8; elain::Align< 8388608>) => Some( 4194304));
531 test!(#[repr(C, packed( 8388608))] (u8; elain::Align< 16777216>) => Some( 8388608));
532 test!(#[repr(C, packed( 16777216))] (u8; elain::Align< 33554432>) => Some( 16777216));
533 test!(#[repr(C, packed( 33554432))] (u8; elain::Align< 67108864>) => Some( 33554432));
534 test!(#[repr(C, packed( 67108864))] (u8; elain::Align< 33554432>) => Some( 67108864));
535 test!(#[repr(C, packed( 33554432))] (u8; elain::Align<134217728>) => Some( 33554432));
536 test!(#[repr(C, packed(134217728))] (u8; elain::Align<268435456>) => Some(134217728));
537 test!(#[repr(C, packed(268435456))] (u8; elain::Align<268435456>) => Some(268435456));
538 */
539
540 // Test that `align(N)` does not limit the offset of the trailing field.
541 test!(#[repr(C, align( 1))] (u8; elain::Align< 2>) => Some( 2));
542 test!(#[repr(C, align( 2))] (u8; elain::Align< 4>) => Some( 4));
543 test!(#[repr(C, align( 4))] (u8; elain::Align< 8>) => Some( 8));
544 test!(#[repr(C, align( 8))] (u8; elain::Align< 16>) => Some( 16));
545 test!(#[repr(C, align( 16))] (u8; elain::Align< 32>) => Some( 32));
546 test!(#[repr(C, align( 32))] (u8; elain::Align< 64>) => Some( 64));
547 test!(#[repr(C, align( 64))] (u8; elain::Align< 128>) => Some( 128));
548 test!(#[repr(C, align( 128))] (u8; elain::Align< 256>) => Some( 256));
549 test!(#[repr(C, align( 256))] (u8; elain::Align< 512>) => Some( 512));
550 test!(#[repr(C, align( 512))] (u8; elain::Align< 1024>) => Some( 1024));
551 test!(#[repr(C, align( 1024))] (u8; elain::Align< 2048>) => Some( 2048));
552 test!(#[repr(C, align( 2048))] (u8; elain::Align< 4096>) => Some( 4096));
553 test!(#[repr(C, align( 4096))] (u8; elain::Align< 8192>) => Some( 8192));
554 test!(#[repr(C, align( 8192))] (u8; elain::Align< 16384>) => Some( 16384));
555 test!(#[repr(C, align( 16384))] (u8; elain::Align< 32768>) => Some( 32768));
556 test!(#[repr(C, align( 32768))] (u8; elain::Align< 65536>) => Some( 65536));
557 /* Alignments above 65536 are not yet supported.
558 test!(#[repr(C, align( 65536))] (u8; elain::Align< 131072>) => Some( 131072));
559 test!(#[repr(C, align( 131072))] (u8; elain::Align< 262144>) => Some( 262144));
560 test!(#[repr(C, align( 262144))] (u8; elain::Align< 524288>) => Some( 524288));
561 test!(#[repr(C, align( 524288))] (u8; elain::Align< 1048576>) => Some( 1048576));
562 test!(#[repr(C, align( 1048576))] (u8; elain::Align< 2097152>) => Some( 2097152));
563 test!(#[repr(C, align( 2097152))] (u8; elain::Align< 4194304>) => Some( 4194304));
564 test!(#[repr(C, align( 4194304))] (u8; elain::Align< 8388608>) => Some( 8388608));
565 test!(#[repr(C, align( 8388608))] (u8; elain::Align< 16777216>) => Some( 16777216));
566 test!(#[repr(C, align( 16777216))] (u8; elain::Align< 33554432>) => Some( 33554432));
567 test!(#[repr(C, align( 33554432))] (u8; elain::Align< 67108864>) => Some( 67108864));
568 test!(#[repr(C, align( 67108864))] (u8; elain::Align< 33554432>) => Some( 33554432));
569 test!(#[repr(C, align( 33554432))] (u8; elain::Align<134217728>) => Some(134217728));
570 test!(#[repr(C, align(134217728))] (u8; elain::Align<268435456>) => Some(268435456));
571 */
572 }
573
574 // TODO(#29), TODO(https://github.com/rust-lang/rust/issues/69835): Remove
575 // this `cfg` when `size_of_val_raw` is stabilized.
576 #[allow(clippy::decimal_literal_representation)]
577 #[cfg(__INTERNAL_USE_ONLY_NIGHLTY_FEATURES_IN_TESTS)]
578 #[test]
579 fn test_align_of_dst() {
580 // Test that `align_of!` correctly computes the alignment of DSTs.
581 assert_eq!(align_of!([elain::Align<1>]), Some(1));
582 assert_eq!(align_of!([elain::Align<2>]), Some(2));
583 assert_eq!(align_of!([elain::Align<4>]), Some(4));
584 assert_eq!(align_of!([elain::Align<8>]), Some(8));
585 assert_eq!(align_of!([elain::Align<16>]), Some(16));
586 assert_eq!(align_of!([elain::Align<32>]), Some(32));
587 assert_eq!(align_of!([elain::Align<64>]), Some(64));
588 assert_eq!(align_of!([elain::Align<128>]), Some(128));
589 assert_eq!(align_of!([elain::Align<256>]), Some(256));
590 assert_eq!(align_of!([elain::Align<512>]), Some(512));
591 assert_eq!(align_of!([elain::Align<1024>]), Some(1024));
592 assert_eq!(align_of!([elain::Align<2048>]), Some(2048));
593 assert_eq!(align_of!([elain::Align<4096>]), Some(4096));
594 assert_eq!(align_of!([elain::Align<8192>]), Some(8192));
595 assert_eq!(align_of!([elain::Align<16384>]), Some(16384));
596 assert_eq!(align_of!([elain::Align<32768>]), Some(32768));
597 assert_eq!(align_of!([elain::Align<65536>]), Some(65536));
598 /* Alignments above 65536 are not yet supported.
599 assert_eq!(align_of!([elain::Align<131072>]), Some(131072));
600 assert_eq!(align_of!([elain::Align<262144>]), Some(262144));
601 assert_eq!(align_of!([elain::Align<524288>]), Some(524288));
602 assert_eq!(align_of!([elain::Align<1048576>]), Some(1048576));
603 assert_eq!(align_of!([elain::Align<2097152>]), Some(2097152));
604 assert_eq!(align_of!([elain::Align<4194304>]), Some(4194304));
605 assert_eq!(align_of!([elain::Align<8388608>]), Some(8388608));
606 assert_eq!(align_of!([elain::Align<16777216>]), Some(16777216));
607 assert_eq!(align_of!([elain::Align<33554432>]), Some(33554432));
608 assert_eq!(align_of!([elain::Align<67108864>]), Some(67108864));
609 assert_eq!(align_of!([elain::Align<33554432>]), Some(33554432));
610 assert_eq!(align_of!([elain::Align<134217728>]), Some(134217728));
611 assert_eq!(align_of!([elain::Align<268435456>]), Some(268435456));
612 */
613 }
614
615 #[test]
616 fn test_struct_has_padding() {
617 // Test that, for each provided repr, `struct_has_padding!` reports the
618 // expected value.
619 macro_rules! test {
620 (#[$cfg:meta] ($($ts:ty),*) => $expect:expr) => {{
621 #[$cfg]
622 #[allow(dead_code)] // fields are never read
623 struct Test($($ts),*);
624 assert_eq!(struct_has_padding!(Test, $($ts),*), $expect);
625 }};
626 (#[$cfg:meta] $(#[$cfgs:meta])* ($($ts:ty),*) => $expect:expr) => {
627 test!(#[$cfg] ($($ts),*) => $expect);
628 test!($(#[$cfgs])* ($($ts),*) => $expect);
629 };
630 }
631
632 test!(#[repr(C)] #[repr(transparent)] #[repr(packed)] () => false);
633 test!(#[repr(C)] #[repr(transparent)] #[repr(packed)] (u8) => false);
634 test!(#[repr(C)] #[repr(transparent)] #[repr(packed)] (u8, ()) => false);
635 test!(#[repr(C)] #[repr(packed)] (u8, u8) => false);
636
637 test!(#[repr(C)] (u8, AU64) => true);
638 // Rust won't let you put `#[repr(packed)]` on a type which contains a
639 // `#[repr(align(n > 1))]` type (`AU64`), so we have to use `u64` here.
640 // It's not ideal, but it definitely has align > 1 on /some/ of our CI
641 // targets, and this isn't a particularly complex macro we're testing
642 // anyway.
643 test!(#[repr(packed)] (u8, u64) => false);
644 }
645
646 #[test]
647 fn test_union_has_padding() {
648 // Test that, for each provided repr, `union_has_padding!` reports the
649 // expected value.
650 macro_rules! test {
651 (#[$cfg:meta] {$($fs:ident: $ts:ty),*} => $expect:expr) => {{
652 #[$cfg]
653 #[allow(unused)] // fields are never read
654 union Test{ $($fs: $ts),* }
655 assert_eq!(union_has_padding!(Test, $($ts),*), $expect);
656 }};
657 (#[$cfg:meta] $(#[$cfgs:meta])* {$($fs:ident: $ts:ty),*} => $expect:expr) => {
658 test!(#[$cfg] {$($fs: $ts),*} => $expect);
659 test!($(#[$cfgs])* {$($fs: $ts),*} => $expect);
660 };
661 }
662
663 test!(#[repr(C)] #[repr(packed)] {a: u8} => false);
664 test!(#[repr(C)] #[repr(packed)] {a: u8, b: u8} => false);
665
666 // Rust won't let you put `#[repr(packed)]` on a type which contains a
667 // `#[repr(align(n > 1))]` type (`AU64`), so we have to use `u64` here.
668 // It's not ideal, but it definitely has align > 1 on /some/ of our CI
669 // targets, and this isn't a particularly complex macro we're testing
670 // anyway.
671 test!(#[repr(C)] #[repr(packed)] {a: u8, b: u64} => true);
672 }
673}
674