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Limit maximum alignment in #[repr(align)] to 4K #70193

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Limit maximum alignment in #[repr(align)] to 4K #70193

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290ac8d
Limit maximum alignment in #[repr(align)]
Amanieu Mar 20, 2020
3f1b797
Fix test
Amanieu Mar 20, 2020
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7 changes: 4 additions & 3 deletions src/librustc_attr/builtin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -908,11 +908,12 @@ pub fn find_repr_attrs(sess: &ParseSess, attr: &Attribute) -> Vec<ReprAttr> {
let parse_alignment = |node: &ast::LitKind| -> Result<u32, &'static str> {
if let ast::LitKind::Int(literal, ast::LitIntType::Unsuffixed) = node {
if literal.is_power_of_two() {
// rustc::ty::layout::Align restricts align to <= 2^29
if *literal <= 1 << 29 {
// Many targets don't support global variables
// with alignment greater than the page size.
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And also page size is always at last 4096, I take it? That is left implicit here, right now the comment doesn't entirely match what the code does.

if *literal <= 4096 {
Ok(*literal as u32)
} else {
Err("larger than 2^29")
Err("larger than 4096")
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if we land this, then it would be good to mention what this magic number is about

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Also, let's add a regression test at (4096 + 1).next_power_of_two()

}
} else {
Err("not a power of two")
Expand Down
12 changes: 6 additions & 6 deletions src/test/ui/repr/repr-align.rs
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Expand Up @@ -8,11 +8,11 @@ struct S0(i32);
//~| ERROR: invalid `repr(align)` attribute: not a power of two
struct S1(i32);

#[repr(align(4294967296))] //~ ERROR: invalid `repr(align)` attribute: larger than 2^29
//~| ERROR: invalid `repr(align)` attribute: larger than 2^29
#[repr(align(4294967296))] //~ ERROR: invalid `repr(align)` attribute: larger than 4096
//~| ERROR: invalid `repr(align)` attribute: larger than 4096
struct S2(i32);

#[repr(align(536870912))] // ok: this is the largest accepted alignment
#[repr(align(4096))] // ok: this is the largest accepted alignment
struct S3(i32);

#[repr(align(16.0))] //~ ERROR: invalid `repr(align)` attribute: not an unsuffixed integer
Expand All @@ -23,11 +23,11 @@ enum E0 { A, B }
//~| ERROR: invalid `repr(align)` attribute: not a power of two
enum E1 { A, B }

#[repr(align(4294967296))] //~ ERROR: invalid `repr(align)` attribute: larger than 2^29
//~| ERROR: invalid `repr(align)` attribute: larger than 2^29
#[repr(align(4294967296))] //~ ERROR: invalid `repr(align)` attribute: larger than 4096
//~| ERROR: invalid `repr(align)` attribute: larger than 4096
enum E2 { A, B }

#[repr(align(536870912))] // ok: this is the largest accepted alignment
#[repr(align(4096))] // ok: this is the largest accepted alignment
enum E3 { A, B }

fn main() {}
8 changes: 4 additions & 4 deletions src/test/ui/repr/repr-align.stderr
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Expand Up @@ -10,7 +10,7 @@ error[E0589]: invalid `repr(align)` attribute: not a power of two
LL | #[repr(align(15))]
| ^^^^^^^^^

error[E0589]: invalid `repr(align)` attribute: larger than 2^29
error[E0589]: invalid `repr(align)` attribute: larger than 4096
--> $DIR/repr-align.rs:11:8
|
LL | #[repr(align(4294967296))]
Expand All @@ -28,7 +28,7 @@ error[E0589]: invalid `repr(align)` attribute: not a power of two
LL | #[repr(align(15))]
| ^^^^^^^^^

error[E0589]: invalid `repr(align)` attribute: larger than 2^29
error[E0589]: invalid `repr(align)` attribute: larger than 4096
--> $DIR/repr-align.rs:26:8
|
LL | #[repr(align(4294967296))]
Expand All @@ -46,7 +46,7 @@ error[E0589]: invalid `repr(align)` attribute: not a power of two
LL | #[repr(align(15))]
| ^^^^^^^^^

error[E0589]: invalid `repr(align)` attribute: larger than 2^29
error[E0589]: invalid `repr(align)` attribute: larger than 4096
--> $DIR/repr-align.rs:11:8
|
LL | #[repr(align(4294967296))]
Expand All @@ -64,7 +64,7 @@ error[E0589]: invalid `repr(align)` attribute: not a power of two
LL | #[repr(align(15))]
| ^^^^^^^^^

error[E0589]: invalid `repr(align)` attribute: larger than 2^29
error[E0589]: invalid `repr(align)` attribute: larger than 4096
--> $DIR/repr-align.rs:26:8
|
LL | #[repr(align(4294967296))]
Expand Down
12 changes: 6 additions & 6 deletions src/test/ui/structs-enums/align-struct.rs
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Expand Up @@ -67,9 +67,9 @@ struct AlignContainsPacked4C {

// The align limit was originally smaller (2^15).
// Check that it works with big numbers.
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Irrelevant for crater run but this comment is now wrong.

#[repr(align(0x10000))]
#[repr(align(0x1000))]
struct AlignLarge {
stuff: [u8; 0x10000],
stuff: [u8; 0x1000],
}

union UnionContainsAlign {
Expand Down Expand Up @@ -233,13 +233,13 @@ pub fn main() {
assert!(is_aligned_to(&a, 16));

let mut large = box AlignLarge {
stuff: [0; 0x10000],
stuff: [0; 0x1000],
};
large.stuff[0] = 132;
*large.stuff.last_mut().unwrap() = 102;
assert_eq!(large.stuff[0], 132);
assert_eq!(large.stuff.last(), Some(&102));
assert_eq!(mem::align_of::<AlignLarge>(), 0x10000);
assert_eq!(mem::align_of_val(&*large), 0x10000);
assert!(is_aligned_to(&*large, 0x10000));
assert_eq!(mem::align_of::<AlignLarge>(), 0x1000);
assert_eq!(mem::align_of_val(&*large), 0x1000);
assert!(is_aligned_to(&*large, 0x1000));
}