Auto merge of #2780 - RalfJung:rustup, r=RalfJung

Rustup

Author: bors

rust-version

@@ -1 +1 @@
-f3126500f25114ba4e0ac3e76694dd45a22de56d
+dffea43fc1102bdfe16d88ed412c23d4f0f08d9d

src/borrow_tracker/stacked_borrows/mod.rs

@@ -81,21 +81,18 @@ impl NewPermission {
                         protector: None,
                     }
                 } else if pointee.is_unpin(*cx.tcx, cx.param_env()) {
-                    // A regular full mutable reference.
+                    // A regular full mutable reference. On `FnEntry` this is `noalias` and `dereferenceable`.
                     NewPermission::Uniform {
                         perm: Permission::Unique,
                         access: Some(AccessKind::Write),
                         protector,
                     }
                 } else {
+                    // `!Unpin` dereferences do not get `noalias` nor `dereferenceable`.
                     NewPermission::Uniform {
                         perm: Permission::SharedReadWrite,
-                        // FIXME: We emit `dereferenceable` for `!Unpin` mutable references, so we
-                        // should do fake accesses here. But then we run into
-                        // <https://github.com/rust-lang/unsafe-code-guidelines/issues/381>, so for now
-                        // we don't do that.
                         access: None,
-                        protector,
+                        protector: None,
                     }
                 }
             }
@@ -109,6 +106,7 @@ impl NewPermission {
                 }
             }
             ty::Ref(_, _pointee, Mutability::Not) => {
+                // Shared references. If frozen, these get `noalias` and `dereferenceable`; otherwise neither.
                 NewPermission::FreezeSensitive {
                     freeze_perm: Permission::SharedReadOnly,
                     freeze_access: Some(AccessKind::Read),
@@ -137,6 +135,31 @@ impl NewPermission {
         }
     }
 
+    fn from_box_ty<'tcx>(
+        ty: Ty<'tcx>,
+        kind: RetagKind,
+        cx: &crate::MiriInterpCx<'_, 'tcx>,
+    ) -> Self {
+        // `ty` is not the `Box` but the field of the Box with this pointer (due to allocator handling).
+        let pointee = ty.builtin_deref(true).unwrap().ty;
+        if pointee.is_unpin(*cx.tcx, cx.param_env()) {
+            // A regular box. On `FnEntry` this is `noalias`, but not `dereferenceable` (hence only
+            // a weak protector).
+            NewPermission::Uniform {
+                perm: Permission::Unique,
+                access: Some(AccessKind::Write),
+                protector: (kind == RetagKind::FnEntry).then_some(ProtectorKind::WeakProtector),
+            }
+        } else {
+            // `!Unpin` boxes do not get `noalias` nor `dereferenceable`.
+            NewPermission::Uniform {
+                perm: Permission::SharedReadWrite,
+                access: None,
+                protector: None,
+            }
+        }
+    }
+
     fn protector(&self) -> Option<ProtectorKind> {
         match self {
             NewPermission::Uniform { protector, .. } => *protector,
@@ -916,12 +939,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
             fn visit_box(&mut self, place: &PlaceTy<'tcx, Provenance>) -> InterpResult<'tcx> {
                 // Boxes get a weak protectors, since they may be deallocated.
-                let new_perm = NewPermission::Uniform {
-                    perm: Permission::Unique,
-                    access: Some(AccessKind::Write),
-                    protector: (self.kind == RetagKind::FnEntry)
-                        .then_some(ProtectorKind::WeakProtector),
-                };
+                let new_perm = NewPermission::from_box_ty(place.layout.ty, self.kind, self.ecx);
                 self.retag_ptr_inplace(place, new_perm, self.retag_cause)
             }
 

tests/fail/stacked_borrows/deallocate_against_protector2.rs

@@ -26,6 +26,19 @@ impl Future for Delay {
     }
 }
 
+fn mk_waker() -> Waker {
+    use std::sync::Arc;
+
+    struct MyWaker;
+    impl Wake for MyWaker {
+        fn wake(self: Arc<Self>) {
+            unimplemented!()
+        }
+    }
+
+    Waker::from(Arc::new(MyWaker))
+}
+
 async fn do_stuff() {
     (&mut Delay::new(1)).await;
 }
@@ -73,16 +86,7 @@ impl Future for DoStuff {
 }
 
 fn run_fut<T>(fut: impl Future<Output = T>) -> T {
-    use std::sync::Arc;
-
-    struct MyWaker;
-    impl Wake for MyWaker {
-        fn wake(self: Arc<Self>) {
-            unimplemented!()
-        }
-    }
-
-    let waker = Waker::from(Arc::new(MyWaker));
+    let waker = mk_waker();
     let mut context = Context::from_waker(&waker);
 
     let mut pinned = pin!(fut);
@@ -94,7 +98,37 @@ fn run_fut<T>(fut: impl Future<Output = T>) -> T {
     }
 }
 
+fn self_referential_box() {
+    let waker = mk_waker();
+    let cx = &mut Context::from_waker(&waker);
+
+    async fn my_fut() -> i32 {
+        let val = 10;
+        let val_ref = &val;
+
+        let _ = Delay::new(1).await;
+
+        *val_ref
+    }
+
+    fn box_poll<F: Future>(
+        mut f: Pin<Box<F>>,
+        cx: &mut Context<'_>,
+    ) -> (Pin<Box<F>>, Poll<F::Output>) {
+        let p = f.as_mut().poll(cx);
+        (f, p)
+    }
+
+    let my_fut = Box::pin(my_fut());
+    let (my_fut, p1) = box_poll(my_fut, cx);
+    assert!(p1.is_pending());
+    let (my_fut, p2) = box_poll(my_fut, cx);
+    assert!(p2.is_ready());
+    drop(my_fut);
+}
+
 fn main() {
     run_fut(do_stuff());
     run_fut(DoStuff::new());
+    self_referential_box();
 }

tests/fail/stacked_borrows/deallocate_against_protector2.stderr

@@ -19,6 +19,7 @@ fn main() {
     array_casts();
     mut_below_shr();
     wide_raw_ptr_in_tuple();
+    not_unpin_not_protected();
 }
 
 // Make sure that reading from an `&mut` does, like reborrowing to `&`,
@@ -219,3 +220,22 @@ fn wide_raw_ptr_in_tuple() {
     // Make sure the fn ptr part of the vtable is still fine.
     r.type_id();
 }
+
+fn not_unpin_not_protected() {
+    // `&mut !Unpin`, at least for now, does not get `noalias` nor `dereferenceable`, so we also
+    // don't add protectors. (We could, but until we have a better idea for where we want to go with
+    // the self-referntial-generator situation, it does not seem worth the potential trouble.)
+    use std::marker::PhantomPinned;
+
+    pub struct NotUnpin(i32, PhantomPinned);
+
+    fn inner(x: &mut NotUnpin, f: fn(&mut NotUnpin)) {
+        // `f` may mutate, but it may not deallocate!
+        f(x)
+    }
+
+    inner(Box::leak(Box::new(NotUnpin(0, PhantomPinned))), |x| {
+        let raw = x as *mut _;
+        drop(unsafe { Box::from_raw(raw) });
+    });
+}