40 lines
1014 B
Rust
40 lines
1014 B
Rust
//@ run-pass
|
|
#![feature(layout_for_ptr)]
|
|
use std::mem;
|
|
|
|
#[repr(packed(4))]
|
|
struct Slice(#[allow(dead_code)] [u32]);
|
|
|
|
#[repr(packed(2), C)]
|
|
struct PackedSized {
|
|
f: u8,
|
|
d: [u32; 4],
|
|
}
|
|
|
|
#[repr(packed(2), C)]
|
|
struct PackedUnsized {
|
|
f: u8,
|
|
d: Slice,
|
|
}
|
|
|
|
impl PackedSized {
|
|
fn unsize(&self) -> &PackedUnsized {
|
|
// We can't unsize via a generic type since then we get the error
|
|
// that packed structs with unsized tail don't work if the tail
|
|
// might need dropping.
|
|
let len = 4usize;
|
|
unsafe { mem::transmute((self, len)) }
|
|
}
|
|
}
|
|
|
|
fn main() { unsafe {
|
|
let p = PackedSized { f: 0, d: [1, 2, 3, 4] };
|
|
let p = p.unsize() as *const PackedUnsized;
|
|
// Make sure the size computation correctly adds exact 1 byte of padding
|
|
// in front of the `d` field.
|
|
assert_eq!(mem::size_of_val_raw(p), 1 + 1 + 4*4);
|
|
// And likewise for the offset computation.
|
|
let d = std::ptr::addr_of!((*p).d);
|
|
assert_eq!(d.cast::<u32>().read_unaligned(), 1);
|
|
} }
|