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add_retag: ensure box-to-raw-ptr casts are preserved for Miri

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This commit is contained in:
Ralf Jung 2024-03-17 17:02:38 +01:00
parent a42873e85b
commit c96fa5e143
10 changed files with 91 additions and 33 deletions
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17
library/alloc/src/boxed.rs
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@ -155,7 +155,6 @@ use core::error::Error;
use core::fmt;
use core::future::Future;
use core::hash::{Hash, Hasher};
use core::intrinsics::retag_box_to_raw;
use core::iter::FusedIterator;
use core::marker::Tuple;
use core::marker::Unsize;
@ -165,7 +164,7 @@ use core::ops::{
CoerceUnsized, Coroutine, CoroutineState, Deref, DerefMut, DispatchFromDyn, Receiver,
};
use core::pin::Pin;
use core::ptr::{self, NonNull, Unique};
use core::ptr::{self, addr_of_mut, NonNull, Unique};
use core::task::{Context, Poll};
#[cfg(not(no_global_oom_handling))]
@ -1111,16 +1110,12 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
#[unstable(feature = "allocator_api", issue = "32838")]
#[inline]
pub fn into_raw_with_allocator(b: Self) -> (*mut T, A) {
// This is the transition point from `Box` to raw pointers. For Stacked Borrows, these casts
// are relevant -- if this is a global allocator Box and we just get the pointer from `b.0`,
// it will have `Unique` permission, which is not what we want from a raw pointer. We could
// fix that by going through `&mut`, but then if this is *not* a global allocator Box, we'd
// be adding uniqueness assertions that we do not want. So for Miri's sake we pass this
// pointer through an intrinsic for box-to-raw casts, which can do the right thing wrt the
// aliasing model.
let b = mem::ManuallyDrop::new(b);
let mut b = mem::ManuallyDrop::new(b);
// We carefully get the raw pointer out in a way that Miri's aliasing model understands what
// is happening: using the primitive "deref" of `Box`.
let ptr = addr_of_mut!(**b);
let alloc = unsafe { ptr::read(&b.1) };
(unsafe { retag_box_to_raw::<T, A>(b.0.as_ptr()) }, alloc)
(ptr, alloc)
}
#[unstable(