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//@compile-flags: -Zmiri-symbolic-alignment-check
use std::mem;
fn test_align_to() {
const N: usize = 4;
let d = Box::new([0u32; N]);
// Get u8 slice covering the entire thing
let s = unsafe { std::slice::from_raw_parts(d.as_ptr() as *const u8, 4 * N) };
let raw = s.as_ptr();
// Cases where we get the expected "middle" part without any fuzz, since the allocation is
// 4-aligned.
{
let (l, m, r) = unsafe { s.align_to::<u32>() };
assert_eq!(l.len(), 0);
assert_eq!(r.len(), 0);
assert_eq!(m.len(), N);
assert_eq!(raw, m.as_ptr() as *const u8);
}
{
let (l, m, r) = unsafe { s[1..].align_to::<u32>() };
assert_eq!(l.len(), 3);
assert_eq!(m.len(), N - 1);
assert_eq!(r.len(), 0);
assert_eq!(raw.wrapping_offset(4), m.as_ptr() as *const u8);
}
{
let (l, m, r) = unsafe { s[..4 * N - 1].align_to::<u32>() };
assert_eq!(l.len(), 0);
assert_eq!(m.len(), N - 1);
assert_eq!(r.len(), 3);
assert_eq!(raw, m.as_ptr() as *const u8);
}
{
let (l, m, r) = unsafe { s[1..4 * N - 1].align_to::<u32>() };
assert_eq!(l.len(), 3);
assert_eq!(m.len(), N - 2);
assert_eq!(r.len(), 3);
assert_eq!(raw.wrapping_offset(4), m.as_ptr() as *const u8);
}
// Cases where we request more alignment than the allocation has.
{
#[repr(align(8))]
#[derive(Copy, Clone)]
struct Align8(#[allow(dead_code)] u64);
let (_l, m, _r) = unsafe { s.align_to::<Align8>() };
assert!(m.len() > 0);
// Ensure the symbolic alignment check has been informed that this is okay now.
let _val = m[0];
}
}
fn test_from_utf8() {
// uses `align_offset` internally
const N: usize = 10;
let vec = vec![0x4141414141414141u64; N];
let content = unsafe { std::slice::from_raw_parts(vec.as_ptr() as *const u8, 8 * N) };
assert_eq!(
std::str::from_utf8(content).unwrap(),
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
);
}
fn test_u64_array() {
#[derive(Default)]
#[repr(align(8))]
struct AlignToU64<T>(T);
const BYTE_LEN: usize = mem::size_of::<[u64; 4]>();
type Data = AlignToU64<[u8; BYTE_LEN]>;
fn example(data: &Data) {
let (head, u64_arrays, tail) = unsafe { data.0.align_to::<[u64; 4]>() };
assert!(head.is_empty(), "buffer was not aligned for 64-bit numbers");
assert_eq!(u64_arrays.len(), 1, "buffer was not long enough");
assert!(tail.is_empty(), "buffer was too long");
let u64_array = &u64_arrays[0];
let _val = u64_array[0]; // make sure we can actually load this
}
example(&Data::default());
}
fn test_cstr() {
// uses `align_offset` internally
std::ffi::CStr::from_bytes_with_nul(b"this is a test that is longer than 16 bytes\0").unwrap();
}
fn huge_align() {
#[cfg(target_pointer_width = "64")]
const SIZE: usize = 1 << 47;
#[cfg(target_pointer_width = "32")]
const SIZE: usize = 1 << 30;
#[cfg(target_pointer_width = "16")]
const SIZE: usize = 1 << 13;
struct HugeSize(#[allow(dead_code)] [u8; SIZE - 1]);
let _ = std::ptr::without_provenance::<HugeSize>(SIZE).align_offset(SIZE);
}
// This shows that we cannot store the promised alignment info in `AllocExtra`,
// since vtables do not have an `AllocExtra`.
fn vtable() {
#[cfg(target_pointer_width = "64")]
type TWOPTR = u128;
#[cfg(target_pointer_width = "32")]
type TWOPTR = u64;
let ptr: &dyn Send = &0;
let parts: (*const (), *const u8) = unsafe { mem::transmute(ptr) };
let vtable = parts.1;
let offset = vtable.align_offset(mem::align_of::<TWOPTR>());
let vtable_aligned = vtable.wrapping_add(offset) as *const [TWOPTR; 0];
// Zero-sized deref, so no in-bounds requirement.
let _place = unsafe { &*vtable_aligned };
}
fn main() {
test_align_to();
test_from_utf8();
test_u64_array();
test_cstr();
huge_align();
vtable();
}
|
