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fix detecting references to packed unsized fields #115583

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merged 2 commits into from
Oct 7, 2023
Merged

fix detecting references to packed unsized fields #115583

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8b3435c
fix detecting references to packed unsized fields
RalfJung Sep 5, 2023
ad7045e
still accept references to u8 slices and str in packed fields
RalfJung Sep 5, 2023
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fix detecting references to packed unsized fields
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@RalfJung
RalfJung committed Sep 5, 2023
commit 8b3435c10f458b840d9cba31f2f35586e9b31189
4 changes: 3 additions & 1 deletion compiler/rustc_const_eval/src/util/alignment.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,9 22,11 @@ where

let ty = place.ty(local_decls, tcx).ty;
match tcx.layout_of(param_env.and(ty)) {
Ok(layout) if layout.align.abi <= pack => {
Ok(layout) if layout.align.abi <= pack && layout.is_sized() => {
// If the packed alignment is greater or equal to the field alignment, the type won't be
// further disaligned.
// However we need to ensure the field is sized; for unsized fields, `layout.align` is
// just an approximation.
debug!(
"is_disaligned({:?}) - align = {}, packed = {}; not disaligned",
place,
Expand Down
13 changes: 13 additions & 0 deletions tests/ui/lint/unaligned_references.rs
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@@ -1,3 1,6 @@
use std::mem::ManuallyDrop;
use std::fmt::Debug;

#[repr(packed)]
pub struct Good {
data: u64,
Expand Down Expand Up @@ -27,6 30,16 @@ impl Foo for Packed2 {
}
}

// Test for #115396
fn packed_dyn() {
#[repr(packed)]
struct Unaligned<T: ? Sized>(ManuallyDrop<T>);

let ref local = Unaligned(ManuallyDrop::new([3, 5, 8u64]));
let foo: &Unaligned<dyn Debug> = &*local;
println!("{:?}", &*foo.0); //~ ERROR reference to packed field
}

fn main() {
unsafe {
let good = Good { data: 0, ptr: &0, data2: [0, 0], aligned: [0; 32] };
Expand Down
32 changes: 21 additions & 11 deletions tests/ui/lint/unaligned_references.stderr
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@@ -1,5 1,5 @@
error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:25:13
--> $DIR/unaligned_references.rs:28:13
|
LL | &self.x;
| ^^^^^^^
Expand All @@ -9,7 9,17 @@ LL | &self.x;
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:34:17
--> $DIR/unaligned_references.rs:40:24
|
LL | println!("{:?}", &*foo.0);
| ^^^^^
|
= note: packed structs are only aligned by one byte, and many modern architectures penalize unaligned field accesses
= note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:47:17
|
LL | let _ = &good.ptr;
| ^^^^^^^^^
Expand All @@ -19,7 29,7 @@ LL | let _ = &good.ptr;
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:35:17
--> $DIR/unaligned_references.rs:48:17
|
LL | let _ = &good.data;
| ^^^^^^^^^^
Expand All @@ -29,7 39,7 @@ LL | let _ = &good.data;
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:37:17
--> $DIR/unaligned_references.rs:50:17
|
LL | let _ = &good.data as *const _;
| ^^^^^^^^^^
Expand All @@ -39,7 49,7 @@ LL | let _ = &good.data as *const _;
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:38:27
--> $DIR/unaligned_references.rs:51:27
|
LL | let _: *const _ = &good.data;
| ^^^^^^^^^^
Expand All @@ -49,7 59,7 @@ LL | let _: *const _ = &good.data;
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:40:17
--> $DIR/unaligned_references.rs:53:17
|
LL | let _ = good.data.clone();
| ^^^^^^^^^
Expand All @@ -59,7 69,7 @@ LL | let _ = good.data.clone();
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:42:17
--> $DIR/unaligned_references.rs:55:17
|
LL | let _ = &good.data2[0];
| ^^^^^^^^^^^^^^
Expand All @@ -69,7 79,7 @@ LL | let _ = &good.data2[0];
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:51:17
--> $DIR/unaligned_references.rs:64:17
|
LL | let _ = &packed2.x;
| ^^^^^^^^^^
Expand All @@ -79,7 89,7 @@ LL | let _ = &packed2.x;
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:90:20
--> $DIR/unaligned_references.rs:103:20
|
LL | let _ref = &m1.1.a;
| ^^^^^^^
Expand All @@ -89,7 99,7 @@ LL | let _ref = &m1.1.a;
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error[E0793]: reference to packed field is unaligned
--> $DIR/unaligned_references.rs:93:20
--> $DIR/unaligned_references.rs:106:20
|
LL | let _ref = &m2.1.a;
| ^^^^^^^
Expand All @@ -98,6 108,6 @@ LL | let _ref = &m2.1.a;
= note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
= help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)

error: aborting due to 10 previous errors
error: aborting due to 11 previous errors

For more information about this error, try `rustc --explain E0793`.
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