Miri subtree update

src/tools/miri/rust-version

@@ -1 +1 @@
-99b7134389e9766462601a2fc4013840b9d31745
+a526d7ce45fd2284e0e7c7556ccba2425b9d25e5

src/tools/miri/src/bin/miri.rs

@@ -620,6 +620,14 @@ fn main() {
             "-Zmiri-unique-is-unique only has an effect when -Zmiri-tree-borrows is also used"
         );
     }
+    // Tree Borrows + permissive provenance does not work.
+    if miri_config.provenance_mode == ProvenanceMode::Permissive
+        && matches!(miri_config.borrow_tracker, Some(BorrowTrackerMethod::TreeBorrows))
+    {
+        show_error!(
+            "Tree Borrows does not support integer-to-pointer casts, and is hence not compatible with permissive provenance"
+        );
+    }
 
     debug!("rustc arguments: {:?}", rustc_args);
     debug!("crate arguments: {:?}", miri_config.args);

src/tools/miri/src/borrow_tracker/mod.rs

@@ -232,6 +232,10 @@ impl GlobalStateInner {
     pub fn remove_unreachable_allocs(&mut self, allocs: &LiveAllocs<'_, '_>) {
         self.root_ptr_tags.retain(|id, _| allocs.is_live(*id));
     }
+
+    pub fn borrow_tracker_method(&self) -> BorrowTrackerMethod {
+        self.borrow_tracker_method
+    }
 }
 
 /// Which borrow tracking method to use

src/tools/miri/src/borrow_tracker/stacked_borrows/mod.rs

@@ -5,6 +5,7 @@ pub mod diagnostics;
 mod item;
 mod stack;
 
+use std::cell::RefCell;
 use std::cmp;
 use std::fmt::Write;
 use std::mem;
@@ -820,7 +821,19 @@ trait EvalContextPrivExt<'tcx, 'ecx>: crate::MiriInterpCxExt<'tcx> {
         // See https://github.com/rust-lang/unsafe-code-guidelines/issues/276.
         let size = match size {
             Some(size) => size,
-            None => return Ok(place.clone()),
+            None => {
+                // The first time this happens, show a warning.
+                thread_local! { static WARNING_SHOWN: RefCell<bool> = const { RefCell::new(false) }; }
+                WARNING_SHOWN.with_borrow_mut(|shown| {
+                    if *shown {
+                        return;
+                    }
+                    // Not yet shown. Show it!
+                    *shown = true;
+                    this.emit_diagnostic(NonHaltingDiagnostic::ExternTypeReborrow);
+                });
+                return Ok(place.clone());
+            }
         };
 
         // Compute new borrow.

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -141,8 +141,15 @@ impl<'tcx> NewPermission {
     ) -> Option<Self> {
         let ty_is_freeze = pointee.is_freeze(*cx.tcx, cx.param_env());
         let ty_is_unpin = pointee.is_unpin(*cx.tcx, cx.param_env());
+        let is_protected = kind == RetagKind::FnEntry;
+        // As demonstrated by `tests/fail/tree_borrows/reservedim_spurious_write.rs`,
+        // interior mutability and protectors interact poorly.
+        // To eliminate the case of Protected Reserved IM we override interior mutability
+        // in the case of a protected reference: protected references are always considered
+        // "freeze".
         let initial_state = match mutability {
-            Mutability::Mut if ty_is_unpin => Permission::new_reserved(ty_is_freeze),
+            Mutability::Mut if ty_is_unpin =>
+                Permission::new_reserved(ty_is_freeze || is_protected),
             Mutability::Not if ty_is_freeze => Permission::new_frozen(),
             // Raw pointers never enter this function so they are not handled.
             // However raw pointers are not the only pointers that take the parent
@@ -151,7 +158,7 @@ impl<'tcx> NewPermission {
             _ => return None,
         };
 
-        let protector = (kind == RetagKind::FnEntry).then_some(ProtectorKind::StrongProtector);
+        let protector = is_protected.then_some(ProtectorKind::StrongProtector);
         Some(Self { zero_size: false, initial_state, protector })
     }
 

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -22,6 +22,11 @@ enum PermissionPriv {
     /// - foreign-read then child-write is UB due to `conflicted`,
     /// - child-write then foreign-read is UB since child-write will activate and then
     ///   foreign-read disables a protected `Active`, which is UB.
+    ///
+    /// Note: since the discovery of `tests/fail/tree_borrows/reservedim_spurious_write.rs`,
+    /// `ty_is_freeze` does not strictly mean that the type has no interior mutability,
+    /// it could be an interior mutable type that lost its interior mutability privileges
+    /// when retagged with a protector.
     Reserved { ty_is_freeze: bool, conflicted: bool },
     /// represents: a unique pointer;
     /// allows: child reads, child writes;
@@ -141,6 +146,12 @@ mod transition {
     /// non-protected interior mutable `Reserved` which stay the same.
     fn foreign_write(state: PermissionPriv, protected: bool) -> Option<PermissionPriv> {
         Some(match state {
+            // FIXME: since the fix related to reservedim_spurious_write, it is now possible
+            // to express these transitions of the state machine without an explicit dependency
+            // on `protected`: because `ty_is_freeze: false` implies `!protected` then
+            // the line handling `Reserved { .. } if protected` could be deleted.
+            // This will however require optimizations to the exhaustive tests because
+            // fewer initial conditions are valid.
             Reserved { .. } if protected => Disabled,
             res @ Reserved { ty_is_freeze: false, .. } => res,
             _ => Disabled,