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Avoid the UB of a null reference to a slice

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This commit is contained in:
Josh Stone 2017-09-29 13:19:20 -07:00
parent 3580c4c589
commit 8b2e09ffbb
1 changed files with 24 additions and 10 deletions
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34
src/libcore/tests/ptr.rs
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@ -8,10 +8,26 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use core::mem;
use core::ptr::*;
use core::slice;
use core::cell::RefCell;
/// Create a null pointer to a mutable slice. This is implemented like
/// `slice::from_raw_parts_mut`, which we can't use directly because
/// having a null `&mut [T]` even temporarily is UB.
fn null_slice<T>() -> *mut [T] {
unsafe {
#[repr(C)]
struct Repr<T> {
pub data: *mut T,
pub len: usize,
}
mem::transmute(Repr { data: null_mut::<T>(), len: 0 })
}
}
#[test]
fn test() {
unsafe {
@ -78,13 +94,11 @@ fn test_is_null() {
let mz: *mut [u8] = &mut [];
assert!(!mz.is_null());
unsafe {
let ncs: *const [u8] = slice::from_raw_parts(null(), 0);
assert!(ncs.is_null());
let ncs: *const [u8] = null_slice();
assert!(ncs.is_null());
let nms: *mut [u8] = slice::from_raw_parts_mut(null_mut(), 0);
assert!(nms.is_null());
}
let nms: *mut [u8] = null_slice();
assert!(nms.is_null());
}
#[test]
@ -123,10 +137,10 @@ fn test_as_ref() {
let mz: *mut [u8] = &mut [];
assert_eq!(mz.as_ref(), Some(&[][..]));
let ncs: *const [u8] = slice::from_raw_parts(null(), 0);
let ncs: *const [u8] = null_slice();
assert_eq!(ncs.as_ref(), None);
let nms: *mut [u8] = slice::from_raw_parts_mut(null_mut(), 0);
let nms: *mut [u8] = null_slice();
assert_eq!(nms.as_ref(), None);
}
}
@ -155,7 +169,7 @@ fn test_as_mut() {
let mz: *mut [u8] = &mut [];
assert_eq!(mz.as_mut(), Some(&mut [][..]));
let nms: *mut [u8] = slice::from_raw_parts_mut(null_mut(), 0);
let nms: *mut [u8] = null_slice();
assert_eq!(nms.as_mut(), None);
}
}