add test to make Miri able to detect OOB in memmove

Author: RalfJung

src/mem/impls.rs

@@ -58,7 +58,7 @@ unsafe fn load_aligned_partial(src: *const usize, load_sz: usize) -> usize {
  let chunk_sz = core::mem::size_of::<$ty>();
  if (load_sz & chunk_sz) != 0 {
  // Since we are doing the large reads first, this must still be aligned to `chunk_sz`.
- *(&raw mut out).byte_add(i).cast::<$ty>() = *src.byte_add(i).cast::<$ty>();
+ *(&raw mut out).wrapping_byte_add(i).cast::<$ty>() = *src.wrapping_byte_add(i).cast::<$ty>();
  i |= chunk_sz;
  }
  )+};
@@ -91,7 +91,7 @@ unsafe fn load_aligned_end_partial(src: *const usize, load_sz: usize) -> usize {
  if (load_sz & chunk_sz) != 0 {
  // Since we are doing the small reads first, `start_shift + i` has in the mean
  // time become aligned to `chunk_sz`.
- *(&raw mut out).byte_add(start_shift + i).cast::<$ty>() = *src.byte_add(start_shift + i).cast::<$ty>();
+ *(&raw mut out).wrapping_byte_add(start_shift + i).cast::<$ty>() = *src.wrapping_byte_add(start_shift + i).cast::<$ty>();
  i |= chunk_sz;
  }
  )+};

testcrate/tests/mem.rs

@@ -230,6 +230,27 @@ fn memmove_backward_aligned() {
  }
 }
 
+#[test]
+fn memmove_misaligned_bounds() {
+ // The above test have the downside that the addresses surrounding the range-to-copy are all
+ // still in-bounds, so Miri would not actually complain about OOB accesses. So we also test with
+ // an array that has just the right size. We test a few times to avoid it being accidentally
+ // aligned.
+ for _ in 0..8 {
+ let mut arr = [0u8; 17 + 1];
+ unsafe {
+ // Copy forward...
+ let src = arr.as_ptr().offset(0);
+ let dst = arr.as_mut_ptr().offset(1);
+ assert_eq!(memmove(dst, src, 17), dst);
+ // ... and backward.
+ let src = arr.as_ptr().offset(1);
+ let dst = arr.as_mut_ptr().offset(0);
+ assert_eq!(memmove(dst, src, 17), dst);
+ }
+ }
+}
+
 #[test]
 fn memset_backward_misaligned_nonaligned_start() {
  let mut arr = gen_arr::<32>();