From c96fa5e14345ca334073b32465e0ff3ef4b92ac5 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sun, 17 Mar 2024 17:02:38 +0100 Subject: add_retag: ensure box-to-raw-ptr casts are preserved for Miri --- library/alloc/src/boxed.rs | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) (limited to 'library/alloc') diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs index 304f607000b..f47fe560b07 100644 --- a/library/alloc/src/boxed.rs +++ b/library/alloc/src/boxed.rs @@ -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 Box { #[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::(b.0.as_ptr()) }, alloc) + (ptr, alloc) } #[unstable( -- cgit 1.4.1-3-g733a5