mirror of
https://github.com/rust-lang/rust
synced 2024-10-18 14:33:50 +00:00
7ccc09b210
Fixes https://github.com/rust-lang/rust/issues/93959 This change was accepted in https://rust-lang.github.io/rfcs/2580-ptr-meta.html Note that this changes the signature of **stable** functions. The change should be backward-compatible, but it is **insta-stable** since it cannot (easily, at all?) be made available only through a `#![feature(…)]` opt-in. The RFC also proposed the same change for `NonNull::dangling`, which makes sense it terms of its signature but not in terms of its implementation. `dangling` uses `align_of()` as an address. But what `align_of()` should be for extern types or whether it should be allowed at all remains an open question. This commit depends on https://github.com/rust-lang/rust/pull/93977, which is not yet part of the bootstrap compiler. So `#[cfg]` is used to only apply the change in stage 1+. As far a I know bounds cannot be made conditional with `#[cfg]`, so the entire functions are duplicated. This is unfortunate but temporary. Since this duplication makes it less obvious in the diff, the new definitions differ in: * More permissive bounds (`Thin` instead of implied `Sized`) * Different implementation * Having `rustc_allow_const_fn_unstable(ptr_metadata)`
784 lines
24 KiB
Rust
784 lines
24 KiB
Rust
use core::cell::RefCell;
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use core::num::NonZeroUsize;
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use core::ptr;
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use core::ptr::*;
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use std::fmt::{Debug, Display};
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#[test]
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fn test_const_from_raw_parts() {
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const SLICE: &[u8] = &[1, 2, 3, 4];
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const FROM_RAW: &[u8] = unsafe { &*slice_from_raw_parts(SLICE.as_ptr(), SLICE.len()) };
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assert_eq!(SLICE, FROM_RAW);
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let slice = &[1, 2, 3, 4, 5];
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let from_raw = unsafe { &*slice_from_raw_parts(slice.as_ptr(), 2) };
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assert_eq!(&slice[..2], from_raw);
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}
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#[test]
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fn test() {
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unsafe {
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struct Pair {
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fst: isize,
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snd: isize,
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}
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let mut p = Pair { fst: 10, snd: 20 };
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let pptr: *mut Pair = &mut p;
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let iptr: *mut isize = pptr as *mut isize;
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assert_eq!(*iptr, 10);
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*iptr = 30;
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assert_eq!(*iptr, 30);
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assert_eq!(p.fst, 30);
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*pptr = Pair { fst: 50, snd: 60 };
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assert_eq!(*iptr, 50);
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assert_eq!(p.fst, 50);
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assert_eq!(p.snd, 60);
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let v0 = vec![32000u16, 32001u16, 32002u16];
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let mut v1 = vec![0u16, 0u16, 0u16];
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copy(v0.as_ptr().offset(1), v1.as_mut_ptr().offset(1), 1);
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assert!((v1[0] == 0u16 && v1[1] == 32001u16 && v1[2] == 0u16));
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copy(v0.as_ptr().offset(2), v1.as_mut_ptr(), 1);
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assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 0u16));
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copy(v0.as_ptr(), v1.as_mut_ptr().offset(2), 1);
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assert!((v1[0] == 32002u16 && v1[1] == 32001u16 && v1[2] == 32000u16));
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}
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}
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#[test]
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fn test_is_null() {
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let p: *const isize = null();
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assert!(p.is_null());
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let q = p.wrapping_offset(1);
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assert!(!q.is_null());
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let mp: *mut isize = null_mut();
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assert!(mp.is_null());
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let mq = mp.wrapping_offset(1);
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assert!(!mq.is_null());
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// Pointers to unsized types -- slices
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let s: &mut [u8] = &mut [1, 2, 3];
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let cs: *const [u8] = s;
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assert!(!cs.is_null());
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let ms: *mut [u8] = s;
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assert!(!ms.is_null());
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let cz: *const [u8] = &[];
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assert!(!cz.is_null());
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let mz: *mut [u8] = &mut [];
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assert!(!mz.is_null());
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let ncs: *const [u8] = null::<[u8; 3]>();
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assert!(ncs.is_null());
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let nms: *mut [u8] = null_mut::<[u8; 3]>();
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assert!(nms.is_null());
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// Pointers to unsized types -- trait objects
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let ci: *const dyn ToString = &3;
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assert!(!ci.is_null());
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let mi: *mut dyn ToString = &mut 3;
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assert!(!mi.is_null());
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let nci: *const dyn ToString = null::<isize>();
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assert!(nci.is_null());
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let nmi: *mut dyn ToString = null_mut::<isize>();
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assert!(nmi.is_null());
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#[cfg(not(bootstrap))]
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{
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extern "C" {
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type Extern;
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}
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let ec: *const Extern = null::<Extern>();
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assert!(ec.is_null());
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let em: *mut Extern = null_mut::<Extern>();
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assert!(em.is_null());
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}
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}
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#[test]
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fn test_as_ref() {
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unsafe {
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let p: *const isize = null();
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assert_eq!(p.as_ref(), None);
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let q: *const isize = &2;
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assert_eq!(q.as_ref().unwrap(), &2);
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let p: *mut isize = null_mut();
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assert_eq!(p.as_ref(), None);
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let q: *mut isize = &mut 2;
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assert_eq!(q.as_ref().unwrap(), &2);
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// Lifetime inference
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let u = 2isize;
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{
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let p = &u as *const isize;
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assert_eq!(p.as_ref().unwrap(), &2);
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}
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// Pointers to unsized types -- slices
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let s: &mut [u8] = &mut [1, 2, 3];
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let cs: *const [u8] = s;
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assert_eq!(cs.as_ref(), Some(&*s));
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let ms: *mut [u8] = s;
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assert_eq!(ms.as_ref(), Some(&*s));
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let cz: *const [u8] = &[];
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assert_eq!(cz.as_ref(), Some(&[][..]));
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let mz: *mut [u8] = &mut [];
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assert_eq!(mz.as_ref(), Some(&[][..]));
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let ncs: *const [u8] = null::<[u8; 3]>();
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assert_eq!(ncs.as_ref(), None);
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let nms: *mut [u8] = null_mut::<[u8; 3]>();
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assert_eq!(nms.as_ref(), None);
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// Pointers to unsized types -- trait objects
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let ci: *const dyn ToString = &3;
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assert!(ci.as_ref().is_some());
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let mi: *mut dyn ToString = &mut 3;
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assert!(mi.as_ref().is_some());
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let nci: *const dyn ToString = null::<isize>();
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assert!(nci.as_ref().is_none());
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let nmi: *mut dyn ToString = null_mut::<isize>();
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assert!(nmi.as_ref().is_none());
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}
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}
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#[test]
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fn test_as_mut() {
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unsafe {
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let p: *mut isize = null_mut();
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assert!(p.as_mut() == None);
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let q: *mut isize = &mut 2;
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assert!(q.as_mut().unwrap() == &mut 2);
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// Lifetime inference
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let mut u = 2isize;
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{
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let p = &mut u as *mut isize;
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assert!(p.as_mut().unwrap() == &mut 2);
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}
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// Pointers to unsized types -- slices
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let s: &mut [u8] = &mut [1, 2, 3];
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let ms: *mut [u8] = s;
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assert_eq!(ms.as_mut(), Some(&mut [1, 2, 3][..]));
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let mz: *mut [u8] = &mut [];
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assert_eq!(mz.as_mut(), Some(&mut [][..]));
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let nms: *mut [u8] = null_mut::<[u8; 3]>();
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assert_eq!(nms.as_mut(), None);
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// Pointers to unsized types -- trait objects
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let mi: *mut dyn ToString = &mut 3;
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assert!(mi.as_mut().is_some());
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let nmi: *mut dyn ToString = null_mut::<isize>();
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assert!(nmi.as_mut().is_none());
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}
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}
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#[test]
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fn test_ptr_addition() {
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unsafe {
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let xs = vec![5; 16];
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let mut ptr = xs.as_ptr();
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let end = ptr.offset(16);
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while ptr < end {
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assert_eq!(*ptr, 5);
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ptr = ptr.offset(1);
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}
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let mut xs_mut = xs;
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let mut m_ptr = xs_mut.as_mut_ptr();
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let m_end = m_ptr.offset(16);
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while m_ptr < m_end {
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*m_ptr += 5;
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m_ptr = m_ptr.offset(1);
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}
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assert!(xs_mut == vec![10; 16]);
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}
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}
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#[test]
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fn test_ptr_subtraction() {
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unsafe {
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let xs = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
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let mut idx = 9;
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let ptr = xs.as_ptr();
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while idx >= 0 {
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assert_eq!(*(ptr.offset(idx as isize)), idx as isize);
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idx = idx - 1;
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}
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let mut xs_mut = xs;
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let m_start = xs_mut.as_mut_ptr();
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let mut m_ptr = m_start.offset(9);
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loop {
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*m_ptr += *m_ptr;
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if m_ptr == m_start {
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break;
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}
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m_ptr = m_ptr.offset(-1);
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}
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assert_eq!(xs_mut, [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]);
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}
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}
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#[test]
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fn test_set_memory() {
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let mut xs = [0u8; 20];
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let ptr = xs.as_mut_ptr();
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unsafe {
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write_bytes(ptr, 5u8, xs.len());
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}
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assert!(xs == [5u8; 20]);
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}
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#[test]
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fn test_set_memory_const() {
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const XS: [u8; 20] = {
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let mut xs = [0u8; 20];
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let ptr = xs.as_mut_ptr();
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unsafe {
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ptr.write_bytes(5u8, xs.len());
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}
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xs
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};
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assert!(XS == [5u8; 20]);
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}
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#[test]
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fn test_unsized_nonnull() {
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let xs: &[i32] = &[1, 2, 3];
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let ptr = unsafe { NonNull::new_unchecked(xs as *const [i32] as *mut [i32]) };
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let ys = unsafe { ptr.as_ref() };
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let zs: &[i32] = &[1, 2, 3];
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assert!(ys == zs);
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}
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#[test]
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fn test_const_nonnull_new() {
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const {
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assert!(NonNull::new(core::ptr::null_mut::<()>()).is_none());
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let value = &mut 0u32;
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let mut ptr = NonNull::new(value).unwrap();
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unsafe { *ptr.as_mut() = 42 };
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let reference = unsafe { &*ptr.as_ref() };
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assert!(*reference == *value);
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assert!(*reference == 42);
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};
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}
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#[test]
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#[cfg(unix)] // printf may not be available on other platforms
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#[allow(deprecated)] // For SipHasher
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pub fn test_variadic_fnptr() {
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use core::ffi;
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use core::hash::{Hash, SipHasher};
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extern "C" {
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// This needs to use the correct function signature even though it isn't called as some
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// codegen backends make it UB to declare a function with multiple conflicting signatures
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// (like LLVM) while others straight up return an error (like Cranelift).
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fn printf(_: *const ffi::c_char, ...) -> ffi::c_int;
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}
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let p: unsafe extern "C" fn(*const ffi::c_char, ...) -> ffi::c_int = printf;
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let q = p.clone();
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assert_eq!(p, q);
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assert!(!(p < q));
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let mut s = SipHasher::new();
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assert_eq!(p.hash(&mut s), q.hash(&mut s));
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}
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#[test]
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fn write_unaligned_drop() {
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thread_local! {
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static DROPS: RefCell<Vec<u32>> = RefCell::new(Vec::new());
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}
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struct Dropper(u32);
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impl Drop for Dropper {
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fn drop(&mut self) {
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DROPS.with(|d| d.borrow_mut().push(self.0));
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}
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}
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{
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let c = Dropper(0);
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let mut t = Dropper(1);
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unsafe {
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write_unaligned(&mut t, c);
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}
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}
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DROPS.with(|d| assert_eq!(*d.borrow(), [0]));
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}
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#[test]
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fn align_offset_zst() {
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// For pointers of stride = 0, the pointer is already aligned or it cannot be aligned at
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// all, because no amount of elements will align the pointer.
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let mut p = 1;
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while p < 1024 {
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assert_eq!((p as *const ()).align_offset(p), 0);
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if p != 1 {
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assert_eq!(((p + 1) as *const ()).align_offset(p), !0);
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}
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p = (p + 1).next_power_of_two();
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}
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}
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#[test]
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fn align_offset_stride1() {
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// For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
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// number of bytes.
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let mut align = 1;
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while align < 1024 {
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for ptr in 1..2 * align {
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let expected = ptr % align;
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let offset = if expected == 0 { 0 } else { align - expected };
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assert_eq!(
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(ptr as *const u8).align_offset(align),
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offset,
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"ptr = {}, align = {}, size = 1",
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ptr,
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align
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);
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}
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align = (align + 1).next_power_of_two();
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}
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}
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#[test]
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fn align_offset_weird_strides() {
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#[repr(packed)]
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struct A3(u16, u8);
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struct A4(u32);
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#[repr(packed)]
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struct A5(u32, u8);
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#[repr(packed)]
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struct A6(u32, u16);
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#[repr(packed)]
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struct A7(u32, u16, u8);
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#[repr(packed)]
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struct A8(u32, u32);
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#[repr(packed)]
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struct A9(u32, u32, u8);
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#[repr(packed)]
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struct A10(u32, u32, u16);
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unsafe fn test_weird_stride<T>(ptr: *const T, align: usize) -> bool {
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let numptr = ptr as usize;
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let mut expected = usize::MAX;
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// Naive but definitely correct way to find the *first* aligned element of stride::<T>.
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for el in 0..align {
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if (numptr + el * ::std::mem::size_of::<T>()) % align == 0 {
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expected = el;
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break;
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}
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}
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let got = ptr.align_offset(align);
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if got != expected {
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eprintln!(
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"aligning {:p} (with stride of {}) to {}, expected {}, got {}",
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ptr,
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::std::mem::size_of::<T>(),
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align,
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expected,
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got
|
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);
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return true;
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}
|
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return false;
|
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}
|
||
|
||
// For pointers of stride != 1, we verify the algorithm against the naivest possible
|
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// implementation
|
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let mut align = 1;
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let mut x = false;
|
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// Miri is too slow
|
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let limit = if cfg!(miri) { 32 } else { 1024 };
|
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while align < limit {
|
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for ptr in 1usize..4 * align {
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unsafe {
|
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x |= test_weird_stride::<A3>(ptr as *const A3, align);
|
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x |= test_weird_stride::<A4>(ptr as *const A4, align);
|
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x |= test_weird_stride::<A5>(ptr as *const A5, align);
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x |= test_weird_stride::<A6>(ptr as *const A6, align);
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x |= test_weird_stride::<A7>(ptr as *const A7, align);
|
||
x |= test_weird_stride::<A8>(ptr as *const A8, align);
|
||
x |= test_weird_stride::<A9>(ptr as *const A9, align);
|
||
x |= test_weird_stride::<A10>(ptr as *const A10, align);
|
||
}
|
||
}
|
||
align = (align + 1).next_power_of_two();
|
||
}
|
||
assert!(!x);
|
||
}
|
||
|
||
#[test]
|
||
fn offset_from() {
|
||
let mut a = [0; 5];
|
||
let ptr1: *mut i32 = &mut a[1];
|
||
let ptr2: *mut i32 = &mut a[3];
|
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unsafe {
|
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assert_eq!(ptr2.offset_from(ptr1), 2);
|
||
assert_eq!(ptr1.offset_from(ptr2), -2);
|
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assert_eq!(ptr1.offset(2), ptr2);
|
||
assert_eq!(ptr2.offset(-2), ptr1);
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn ptr_metadata() {
|
||
struct Unit;
|
||
struct Pair<A, B: ?Sized>(A, B);
|
||
extern "C" {
|
||
type Extern;
|
||
}
|
||
let () = metadata(&());
|
||
let () = metadata(&Unit);
|
||
let () = metadata(&4_u32);
|
||
let () = metadata(&String::new());
|
||
let () = metadata(&Some(4_u32));
|
||
let () = metadata(&ptr_metadata);
|
||
let () = metadata(&|| {});
|
||
let () = metadata(&[4, 7]);
|
||
let () = metadata(&(4, String::new()));
|
||
let () = metadata(&Pair(4, String::new()));
|
||
let () = metadata(0 as *const Extern);
|
||
let () = metadata(0 as *const <&u32 as std::ops::Deref>::Target);
|
||
|
||
assert_eq!(metadata("foo"), 3_usize);
|
||
assert_eq!(metadata(&[4, 7][..]), 2_usize);
|
||
|
||
let dst_tuple: &(bool, [u8]) = &(true, [0x66, 0x6F, 0x6F]);
|
||
let dst_struct: &Pair<bool, [u8]> = &Pair(true, [0x66, 0x6F, 0x6F]);
|
||
assert_eq!(metadata(dst_tuple), 3_usize);
|
||
assert_eq!(metadata(dst_struct), 3_usize);
|
||
unsafe {
|
||
let dst_tuple: &(bool, str) = std::mem::transmute(dst_tuple);
|
||
let dst_struct: &Pair<bool, str> = std::mem::transmute(dst_struct);
|
||
assert_eq!(&dst_tuple.1, "foo");
|
||
assert_eq!(&dst_struct.1, "foo");
|
||
assert_eq!(metadata(dst_tuple), 3_usize);
|
||
assert_eq!(metadata(dst_struct), 3_usize);
|
||
}
|
||
|
||
let vtable_1: DynMetadata<dyn Debug> = metadata(&4_u16 as &dyn Debug);
|
||
let vtable_2: DynMetadata<dyn Display> = metadata(&4_u16 as &dyn Display);
|
||
let vtable_3: DynMetadata<dyn Display> = metadata(&4_u32 as &dyn Display);
|
||
let vtable_4: DynMetadata<dyn Display> = metadata(&(true, 7_u32) as &(bool, dyn Display));
|
||
let vtable_5: DynMetadata<dyn Display> =
|
||
metadata(&Pair(true, 7_u32) as &Pair<bool, dyn Display>);
|
||
unsafe {
|
||
let address_1: *const () = std::mem::transmute(vtable_1);
|
||
let address_2: *const () = std::mem::transmute(vtable_2);
|
||
let address_3: *const () = std::mem::transmute(vtable_3);
|
||
let address_4: *const () = std::mem::transmute(vtable_4);
|
||
let address_5: *const () = std::mem::transmute(vtable_5);
|
||
// Different trait => different vtable pointer
|
||
assert_ne!(address_1, address_2);
|
||
// Different erased type => different vtable pointer
|
||
assert_ne!(address_2, address_3);
|
||
// Same erased type and same trait => same vtable pointer
|
||
assert_eq!(address_3, address_4);
|
||
assert_eq!(address_3, address_5);
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn ptr_metadata_bounds() {
|
||
fn metadata_eq_method_address<T: ?Sized>() -> usize {
|
||
// The `Metadata` associated type has an `Ord` bound, so this is valid:
|
||
<<T as Pointee>::Metadata as PartialEq>::eq as usize
|
||
}
|
||
// "Synthetic" trait impls generated by the compiler like those of `Pointee`
|
||
// are not checked for bounds of associated type.
|
||
// So with a buggy libcore we could have both:
|
||
// * `<dyn Display as Pointee>::Metadata == DynMetadata`
|
||
// * `DynMetadata: !PartialEq`
|
||
// … and cause an ICE here:
|
||
metadata_eq_method_address::<dyn Display>();
|
||
|
||
// For this reason, let’s check here that bounds are satisfied:
|
||
|
||
let _ = static_assert_expected_bounds_for_metadata::<()>;
|
||
let _ = static_assert_expected_bounds_for_metadata::<usize>;
|
||
let _ = static_assert_expected_bounds_for_metadata::<DynMetadata<dyn Display>>;
|
||
fn _static_assert_associated_type<T: ?Sized>() {
|
||
let _ = static_assert_expected_bounds_for_metadata::<<T as Pointee>::Metadata>;
|
||
}
|
||
|
||
fn static_assert_expected_bounds_for_metadata<Meta>()
|
||
where
|
||
// Keep this in sync with the associated type in `library/core/src/ptr/metadata.rs`
|
||
Meta: Copy + Send + Sync + Ord + std::hash::Hash + Unpin,
|
||
{
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn dyn_metadata() {
|
||
#[derive(Debug)]
|
||
#[repr(align(32))]
|
||
struct Something([u8; 47]);
|
||
|
||
let value = Something([0; 47]);
|
||
let trait_object: &dyn Debug = &value;
|
||
let meta = metadata(trait_object);
|
||
|
||
assert_eq!(meta.size_of(), 64);
|
||
assert_eq!(meta.size_of(), std::mem::size_of::<Something>());
|
||
assert_eq!(meta.align_of(), 32);
|
||
assert_eq!(meta.align_of(), std::mem::align_of::<Something>());
|
||
assert_eq!(meta.layout(), std::alloc::Layout::new::<Something>());
|
||
|
||
assert!(format!("{meta:?}").starts_with("DynMetadata(0x"));
|
||
}
|
||
|
||
#[test]
|
||
fn from_raw_parts() {
|
||
let mut value = 5_u32;
|
||
let address = &mut value as *mut _ as *mut ();
|
||
let trait_object: &dyn Display = &mut value;
|
||
let vtable = metadata(trait_object);
|
||
let trait_object = NonNull::from(trait_object);
|
||
|
||
assert_eq!(ptr::from_raw_parts(address, vtable), trait_object.as_ptr());
|
||
assert_eq!(ptr::from_raw_parts_mut(address, vtable), trait_object.as_ptr());
|
||
assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), vtable), trait_object);
|
||
|
||
let mut array = [5_u32, 5, 5, 5, 5];
|
||
let address = &mut array as *mut _ as *mut ();
|
||
let array_ptr = NonNull::from(&mut array);
|
||
let slice_ptr = NonNull::from(&mut array[..]);
|
||
|
||
assert_eq!(ptr::from_raw_parts(address, ()), array_ptr.as_ptr());
|
||
assert_eq!(ptr::from_raw_parts_mut(address, ()), array_ptr.as_ptr());
|
||
assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), ()), array_ptr);
|
||
|
||
assert_eq!(ptr::from_raw_parts(address, 5), slice_ptr.as_ptr());
|
||
assert_eq!(ptr::from_raw_parts_mut(address, 5), slice_ptr.as_ptr());
|
||
assert_eq!(NonNull::from_raw_parts(NonNull::new(address).unwrap(), 5), slice_ptr);
|
||
}
|
||
|
||
#[test]
|
||
fn thin_box() {
|
||
let foo = ThinBox::<dyn Display>::new(4);
|
||
assert_eq!(foo.to_string(), "4");
|
||
drop(foo);
|
||
let bar = ThinBox::<dyn Display>::new(7);
|
||
assert_eq!(bar.to_string(), "7");
|
||
|
||
// A slightly more interesting library that could be built on top of metadata APIs.
|
||
//
|
||
// * It could be generalized to any `T: ?Sized` (not just trait object)
|
||
// if `{size,align}_of_for_meta<T: ?Sized>(T::Metadata)` are added.
|
||
// * Constructing a `ThinBox` without consuming and deallocating a `Box`
|
||
// requires either the unstable `Unsize` marker trait,
|
||
// or the unstable `unsized_locals` language feature,
|
||
// or taking `&dyn T` and restricting to `T: Copy`.
|
||
|
||
use std::alloc::*;
|
||
use std::marker::PhantomData;
|
||
|
||
struct ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
ptr: NonNull<DynMetadata<T>>,
|
||
phantom: PhantomData<T>,
|
||
}
|
||
|
||
impl<T> ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
pub fn new<Value: std::marker::Unsize<T>>(value: Value) -> Self {
|
||
let unsized_: &T = &value;
|
||
let meta = metadata(unsized_);
|
||
let meta_layout = Layout::for_value(&meta);
|
||
let value_layout = Layout::for_value(&value);
|
||
let (layout, offset) = meta_layout.extend(value_layout).unwrap();
|
||
// `DynMetadata` is pointer-sized:
|
||
assert!(layout.size() > 0);
|
||
// If `ThinBox<T>` is generalized to any `T: ?Sized`,
|
||
// handle ZSTs with a dangling pointer without going through `alloc()`,
|
||
// like `Box<T>` does.
|
||
unsafe {
|
||
let ptr = NonNull::new(alloc(layout))
|
||
.unwrap_or_else(|| handle_alloc_error(layout))
|
||
.cast::<DynMetadata<T>>();
|
||
ptr.as_ptr().write(meta);
|
||
ptr.cast::<u8>().as_ptr().add(offset).cast::<Value>().write(value);
|
||
Self { ptr, phantom: PhantomData }
|
||
}
|
||
}
|
||
|
||
fn meta(&self) -> DynMetadata<T> {
|
||
unsafe { *self.ptr.as_ref() }
|
||
}
|
||
|
||
fn layout(&self) -> (Layout, usize) {
|
||
let meta = self.meta();
|
||
Layout::for_value(&meta).extend(meta.layout()).unwrap()
|
||
}
|
||
|
||
fn value_ptr(&self) -> *const T {
|
||
let (_, offset) = self.layout();
|
||
let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
|
||
ptr::from_raw_parts(data_ptr.cast(), self.meta())
|
||
}
|
||
|
||
fn value_mut_ptr(&mut self) -> *mut T {
|
||
let (_, offset) = self.layout();
|
||
// FIXME: can this line be shared with the same in `value_ptr()`
|
||
// without upsetting Stacked Borrows?
|
||
let data_ptr = unsafe { self.ptr.cast::<u8>().as_ptr().add(offset) };
|
||
from_raw_parts_mut(data_ptr.cast(), self.meta())
|
||
}
|
||
}
|
||
|
||
impl<T> std::ops::Deref for ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
type Target = T;
|
||
|
||
fn deref(&self) -> &T {
|
||
unsafe { &*self.value_ptr() }
|
||
}
|
||
}
|
||
|
||
impl<T> std::ops::DerefMut for ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
fn deref_mut(&mut self) -> &mut T {
|
||
unsafe { &mut *self.value_mut_ptr() }
|
||
}
|
||
}
|
||
|
||
impl<T> std::ops::Drop for ThinBox<T>
|
||
where
|
||
T: ?Sized + Pointee<Metadata = DynMetadata<T>>,
|
||
{
|
||
fn drop(&mut self) {
|
||
let (layout, _) = self.layout();
|
||
unsafe {
|
||
drop_in_place::<T>(&mut **self);
|
||
dealloc(self.ptr.cast().as_ptr(), layout);
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
#[test]
|
||
fn nonnull_tagged_pointer_with_provenance() {
|
||
let raw_pointer = Box::into_raw(Box::new(10));
|
||
|
||
let mut p = TaggedPointer::new(raw_pointer).unwrap();
|
||
assert_eq!(p.tag(), 0);
|
||
|
||
p.set_tag(1);
|
||
assert_eq!(p.tag(), 1);
|
||
assert_eq!(unsafe { *p.pointer().as_ptr() }, 10);
|
||
|
||
p.set_tag(3);
|
||
assert_eq!(p.tag(), 3);
|
||
assert_eq!(unsafe { *p.pointer().as_ptr() }, 10);
|
||
|
||
unsafe { Box::from_raw(p.pointer().as_ptr()) };
|
||
|
||
/// A non-null pointer type which carries several bits of metadata and maintains provenance.
|
||
#[repr(transparent)]
|
||
pub struct TaggedPointer<T>(NonNull<T>);
|
||
|
||
impl<T> Clone for TaggedPointer<T> {
|
||
fn clone(&self) -> Self {
|
||
Self(self.0)
|
||
}
|
||
}
|
||
|
||
impl<T> Copy for TaggedPointer<T> {}
|
||
|
||
impl<T> TaggedPointer<T> {
|
||
/// The ABI-required minimum alignment of the `P` type.
|
||
pub const ALIGNMENT: usize = core::mem::align_of::<T>();
|
||
/// A mask for data-carrying bits of the address.
|
||
pub const DATA_MASK: usize = !Self::ADDRESS_MASK;
|
||
/// Number of available bits of storage in the address.
|
||
pub const NUM_BITS: u32 = Self::ALIGNMENT.trailing_zeros();
|
||
/// A mask for the non-data-carrying bits of the address.
|
||
pub const ADDRESS_MASK: usize = usize::MAX << Self::NUM_BITS;
|
||
|
||
/// Create a new tagged pointer from a possibly null pointer.
|
||
pub fn new(pointer: *mut T) -> Option<TaggedPointer<T>> {
|
||
Some(TaggedPointer(NonNull::new(pointer)?))
|
||
}
|
||
|
||
/// Consume this tagged pointer and produce a raw mutable pointer to the
|
||
/// memory location.
|
||
pub fn pointer(self) -> NonNull<T> {
|
||
// SAFETY: The `addr` guaranteed to have bits set in the Self::ADDRESS_MASK, so the result will be non-null.
|
||
self.0.map_addr(|addr| unsafe {
|
||
NonZeroUsize::new_unchecked(addr.get() & Self::ADDRESS_MASK)
|
||
})
|
||
}
|
||
|
||
/// Consume this tagged pointer and produce the data it carries.
|
||
pub fn tag(&self) -> usize {
|
||
self.0.addr().get() & Self::DATA_MASK
|
||
}
|
||
|
||
/// Update the data this tagged pointer carries to a new value.
|
||
pub fn set_tag(&mut self, data: usize) {
|
||
assert_eq!(
|
||
data & Self::ADDRESS_MASK,
|
||
0,
|
||
"cannot set more data beyond the lowest NUM_BITS"
|
||
);
|
||
let data = data & Self::DATA_MASK;
|
||
|
||
// SAFETY: This value will always be non-zero because the upper bits (from
|
||
// ADDRESS_MASK) will always be non-zero. This a property of the type and its
|
||
// construction.
|
||
self.0 = self.0.map_addr(|addr| unsafe {
|
||
NonZeroUsize::new_unchecked((addr.get() & Self::ADDRESS_MASK) | data)
|
||
})
|
||
}
|
||
}
|
||
}
|