1 // SPDX-License-Identifier: Apache-2.0 OR MIT
2
3 // unaligned_references did not exist in older compilers and safe_packed_borrows was removed in the latest compilers.
4 // https://github.com/rust-lang/rust/pull/82525
5 #![allow(unknown_lints, renamed_and_removed_lints)]
6 #![forbid(unaligned_references, safe_packed_borrows)]
7
8 use std::cell::Cell;
9
10 // Ensure that the compiler doesn't copy the fields
11 // of #[repr(packed)] types during drop, if the field has alignment 1
12 // (that is, any reference to the field is guaranteed to have proper alignment)
13 // We are currently unable to statically prevent the usage of #[pin_project]
14 // on #[repr(packed)] types composed entirely of fields of alignment 1.
15 // This shouldn't lead to undefined behavior, as long as the compiler doesn't
16 // try to move the field anyway during drop.
17 //
18 // This tests validates that the compiler is doing what we expect.
19 #[test]
weird_repr_packed()20 fn weird_repr_packed() {
21 // We keep track of the field address during
22 // drop using a thread local, to avoid changing
23 // the layout of our #[repr(packed)] type.
24 thread_local! {
25 static FIELD_ADDR: Cell<usize> = Cell::new(0);
26 }
27
28 #[repr(packed)]
29 struct Struct {
30 field: u8,
31 }
32
33 impl Drop for Struct {
34 fn drop(&mut self) {
35 FIELD_ADDR.with(|f| {
36 f.set(&self.field as *const u8 as usize);
37 });
38 }
39 }
40
41 let field_addr = {
42 // We let this field drop by going out of scope,
43 // rather than explicitly calling drop(foo).
44 // Calling drop(foo) causes 'foo' to be moved
45 // into the 'drop' function, resulting in a different
46 // address.
47 let x = Struct { field: 27 };
48 &x.field as *const u8 as usize
49 };
50 assert_eq!(field_addr, FIELD_ADDR.with(Cell::get));
51 }
52