Rollup merge of #124030 - RalfJung:adjust_alloc_base_pointer, r=oli-obk

interpret: pass MemoryKind to adjust_alloc_base_pointer

Another puzzle piece for rust-lang#3475.

The 2nd commit renames base_pointer -> root_pointer; that's how Tree Borrows already calls them and I think the term is more clear than "base pointer". In particular, this distinguishes it from "base address", since a root pointer can point anywhere into an allocation, not just its base address.

rust-lang/rust#124018 has been rolled up already so I couldn't add it there any more.

r? ```@oli-obk```

src/alloc_addresses/mod.rs

@@ -141,7 +141,11 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         }
     }
 
-    fn addr_from_alloc_id(&self, alloc_id: AllocId) -> InterpResult<'tcx, u64> {
+    fn addr_from_alloc_id(
+        &self,
+        alloc_id: AllocId,
+        _kind: MemoryKind,
+    ) -> InterpResult<'tcx, u64> {
         let ecx = self.eval_context_ref();
         let mut global_state = ecx.machine.alloc_addresses.borrow_mut();
         let global_state = &mut *global_state;
@@ -283,16 +287,17 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     }
 
     /// Convert a relative (tcx) pointer to a Miri pointer.
-    fn ptr_from_rel_ptr(
+    fn adjust_alloc_root_pointer(
         &self,
         ptr: Pointer<CtfeProvenance>,
         tag: BorTag,
+        kind: MemoryKind,
     ) -> InterpResult<'tcx, Pointer<Provenance>> {
         let ecx = self.eval_context_ref();
 
         let (prov, offset) = ptr.into_parts(); // offset is relative (AllocId provenance)
         let alloc_id = prov.alloc_id();
-        let base_addr = ecx.addr_from_alloc_id(alloc_id)?;
+        let base_addr = ecx.addr_from_alloc_id(alloc_id, kind)?;
 
         // Add offset with the right kind of pointer-overflowing arithmetic.
         let dl = ecx.data_layout();
@@ -314,9 +319,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             ecx.alloc_id_from_addr(addr.bytes())?
         };
 
-        // This cannot fail: since we already have a pointer with that provenance, rel_ptr_to_addr
+        // This cannot fail: since we already have a pointer with that provenance, adjust_alloc_root_pointer
         // must have been called in the past, so we can just look up the address in the map.
-        let base_addr = ecx.addr_from_alloc_id(alloc_id).unwrap();
+        let base_addr = *ecx.machine.alloc_addresses.borrow().base_addr.get(&alloc_id).unwrap();
 
         // Wrapping "addr - base_addr"
         #[allow(clippy::cast_possible_wrap)] // we want to wrap here

src/borrow_tracker/mod.rs

@@ -89,10 +89,10 @@ pub struct GlobalStateInner {
     borrow_tracker_method: BorrowTrackerMethod,
     /// Next unused pointer ID (tag).
     next_ptr_tag: BorTag,
-    /// Table storing the "base" tag for each allocation.
-    /// The base tag is the one used for the initial pointer.
+    /// Table storing the "root" tag for each allocation.
+    /// The root tag is the one used for the initial pointer.
     /// We need this in a separate table to handle cyclic statics.
-    base_ptr_tags: FxHashMap<AllocId, BorTag>,
+    root_ptr_tags: FxHashMap<AllocId, BorTag>,
     /// Next unused call ID (for protectors).
     next_call_id: CallId,
     /// All currently protected tags.
@@ -175,7 +175,7 @@ impl GlobalStateInner {
         GlobalStateInner {
             borrow_tracker_method,
             next_ptr_tag: BorTag::one(),
-            base_ptr_tags: FxHashMap::default(),
+            root_ptr_tags: FxHashMap::default(),
             next_call_id: NonZero::new(1).unwrap(),
             protected_tags: FxHashMap::default(),
             tracked_pointer_tags,
@@ -213,8 +213,8 @@ impl GlobalStateInner {
         }
     }
 
-    pub fn base_ptr_tag(&mut self, id: AllocId, machine: &MiriMachine<'_, '_>) -> BorTag {
-        self.base_ptr_tags.get(&id).copied().unwrap_or_else(|| {
+    pub fn root_ptr_tag(&mut self, id: AllocId, machine: &MiriMachine<'_, '_>) -> BorTag {
+        self.root_ptr_tags.get(&id).copied().unwrap_or_else(|| {
             let tag = self.new_ptr();
             if self.tracked_pointer_tags.contains(&tag) {
                 machine.emit_diagnostic(NonHaltingDiagnostic::CreatedPointerTag(
@@ -223,14 +223,14 @@ impl GlobalStateInner {
                     None,
                 ));
             }
-            trace!("New allocation {:?} has base tag {:?}", id, tag);
-            self.base_ptr_tags.try_insert(id, tag).unwrap();
+            trace!("New allocation {:?} has rpot tag {:?}", id, tag);
+            self.root_ptr_tags.try_insert(id, tag).unwrap();
             tag
         })
     }
 
     pub fn remove_unreachable_allocs(&mut self, allocs: &LiveAllocs<'_, '_, '_>) {
-        self.base_ptr_tags.retain(|id, _| allocs.is_live(*id));
+        self.root_ptr_tags.retain(|id, _| allocs.is_live(*id));
     }
 }
 

src/borrow_tracker/stacked_borrows/diagnostics.rs

@@ -20,7 +20,7 @@ fn err_sb_ub<'tcx>(
 #[derive(Clone, Debug)]
 pub struct AllocHistory {
     id: AllocId,
-    base: (Item, Span),
+    root: (Item, Span),
     creations: smallvec::SmallVec<[Creation; 1]>,
     invalidations: smallvec::SmallVec<[Invalidation; 1]>,
     protectors: smallvec::SmallVec<[Protection; 1]>,
@@ -225,7 +225,7 @@ impl AllocHistory {
     pub fn new(id: AllocId, item: Item, machine: &MiriMachine<'_, '_>) -> Self {
         Self {
             id,
-            base: (item, machine.current_span()),
+            root: (item, machine.current_span()),
             creations: SmallVec::new(),
             invalidations: SmallVec::new(),
             protectors: SmallVec::new(),
@@ -342,15 +342,15 @@ impl<'history, 'ecx, 'mir, 'tcx> DiagnosticCx<'history, 'ecx, 'mir, 'tcx> {
                 })
             })
             .or_else(|| {
-                // If we didn't find a retag that created this tag, it might be the base tag of
+                // If we didn't find a retag that created this tag, it might be the root tag of
                 // this allocation.
-                if self.history.base.0.tag() == tag {
+                if self.history.root.0.tag() == tag {
                     Some((
                         format!(
-                            "{tag:?} was created here, as the base tag for {:?}",
+                            "{tag:?} was created here, as the root tag for {:?}",
                             self.history.id
                         ),
-                        self.history.base.1.data(),
+                        self.history.root.1.data(),
                     ))
                 } else {
                     None

src/borrow_tracker/stacked_borrows/mod.rs

@@ -518,9 +518,9 @@ impl Stacks {
             // not through a pointer). That is, whenever we directly write to a local, this will pop
             // everything else off the stack, invalidating all previous pointers,
             // and in particular, *all* raw pointers.
-            MemoryKind::Stack => (state.base_ptr_tag(id, machine), Permission::Unique),
+            MemoryKind::Stack => (state.root_ptr_tag(id, machine), Permission::Unique),
             // Everything else is shared by default.
-            _ => (state.base_ptr_tag(id, machine), Permission::SharedReadWrite),
+            _ => (state.root_ptr_tag(id, machine), Permission::SharedReadWrite),
         };
         Stacks::new(size, perm, base_tag, id, machine)
     }

src/borrow_tracker/stacked_borrows/stack.rs

@@ -47,7 +47,7 @@ impl Stack {
         let mut first_removed = None;
 
         // We never consider removing the bottom-most tag. For stacks without an unknown
-        // bottom this preserves the base tag.
+        // bottom this preserves the root tag.
         // Note that the algorithm below is based on considering the tag at read_idx - 1,
         // so precisely considering the tag at index 0 for removal when we have an unknown
         // bottom would complicate the implementation. The simplification of not considering
@@ -93,7 +93,7 @@ impl Stack {
                 self.unique_range = 0..self.len();
             }
 
-            // Replace any Items which have been collected with the base item, a known-good value.
+            // Replace any Items which have been collected with the root item, a known-good value.
             for i in 0..CACHE_LEN {
                 if self.cache.idx[i] >= first_removed {
                     self.cache.items[i] = self.borrows[0];
@@ -331,7 +331,7 @@ impl<'tcx> Stack {
         self.verify_cache_consistency();
     }
 
-    /// Construct a new `Stack` using the passed `Item` as the base tag.
+    /// Construct a new `Stack` using the passed `Item` as the root tag.
     pub fn new(item: Item) -> Self {
         Stack {
             borrows: vec![item],
@@ -438,8 +438,8 @@ impl<'tcx> Stack {
             let mut removed = 0;
             let mut cursor = 0;
             // Remove invalid entries from the cache by rotating them to the end of the cache, then
-            // keep track of how many invalid elements there are and overwrite them with the base tag.
-            // The base tag here serves as a harmless default value.
+            // keep track of how many invalid elements there are and overwrite them with the root tag.
+            // The root tag here serves as a harmless default value.
             for _ in 0..CACHE_LEN - 1 {
                 if self.cache.idx[cursor] >= start {
                     self.cache.idx[cursor..CACHE_LEN - removed].rotate_left(1);

src/borrow_tracker/tree_borrows/mod.rs

@@ -37,7 +37,7 @@ impl<'tcx> Tree {
         _kind: MemoryKind,
         machine: &MiriMachine<'_, 'tcx>,
     ) -> Self {
-        let tag = state.base_ptr_tag(id, machine); // Fresh tag for the root
+        let tag = state.root_ptr_tag(id, machine); // Fresh tag for the root
         let span = machine.current_span();
         Tree::new(tag, size, span)
     }

src/machine.rs

@@ -503,7 +503,7 @@ pub struct MiriMachine<'mir, 'tcx> {
     /// Crates which are considered local for the purposes of error reporting.
     pub(crate) local_crates: Vec<CrateNum>,
 
-    /// Mapping extern static names to their base pointer.
+    /// Mapping extern static names to their pointer.
     extern_statics: FxHashMap<Symbol, Pointer<Provenance>>,
 
     /// The random number generator used for resolving non-determinism.
@@ -1042,14 +1042,14 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
         ecx.generate_nan(inputs)
     }
 
-    fn thread_local_static_base_pointer(
+    fn thread_local_static_pointer(
         ecx: &mut MiriInterpCx<'mir, 'tcx>,
         def_id: DefId,
     ) -> InterpResult<'tcx, Pointer<Provenance>> {
         ecx.get_or_create_thread_local_alloc(def_id)
     }
 
-    fn extern_static_base_pointer(
+    fn extern_static_pointer(
         ecx: &MiriInterpCx<'mir, 'tcx>,
         def_id: DefId,
     ) -> InterpResult<'tcx, Pointer<Provenance>> {
@@ -1090,7 +1090,7 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
         alloc: Cow<'b, Allocation>,
         kind: Option<MemoryKind>,
     ) -> InterpResult<'tcx, Cow<'b, Allocation<Self::Provenance, Self::AllocExtra>>> {
-        let kind = kind.expect("we set our STATIC_KIND so this cannot be None");
+        let kind = kind.expect("we set our GLOBAL_KIND so this cannot be None");
         if ecx.machine.tracked_alloc_ids.contains(&id) {
             ecx.emit_diagnostic(NonHaltingDiagnostic::CreatedAlloc(
                 id,
@@ -1135,7 +1135,7 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
                 weak_memory: buffer_alloc,
                 backtrace,
             },
-            |ptr| ecx.global_base_pointer(ptr),
+            |ptr| ecx.global_root_pointer(ptr),
         )?;
 
         if matches!(kind, MemoryKind::Machine(kind) if kind.should_save_allocation_span()) {
@@ -1148,31 +1148,33 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
         Ok(Cow::Owned(alloc))
     }
 
-    fn adjust_alloc_base_pointer(
+    fn adjust_alloc_root_pointer(
         ecx: &MiriInterpCx<'mir, 'tcx>,
         ptr: Pointer<CtfeProvenance>,
+        kind: Option<MemoryKind>,
     ) -> InterpResult<'tcx, Pointer<Provenance>> {
+        let kind = kind.expect("we set our GLOBAL_KIND so this cannot be None");
         let alloc_id = ptr.provenance.alloc_id();
         if cfg!(debug_assertions) {
             // The machine promises to never call us on thread-local or extern statics.
             match ecx.tcx.try_get_global_alloc(alloc_id) {
                 Some(GlobalAlloc::Static(def_id)) if ecx.tcx.is_thread_local_static(def_id) => {
-                    panic!("adjust_alloc_base_pointer called on thread-local static")
+                    panic!("adjust_alloc_root_pointer called on thread-local static")
                 }
                 Some(GlobalAlloc::Static(def_id)) if ecx.tcx.is_foreign_item(def_id) => {
-                    panic!("adjust_alloc_base_pointer called on extern static")
+                    panic!("adjust_alloc_root_pointer called on extern static")
                 }
                 _ => {}
             }
         }
         // FIXME: can we somehow preserve the immutability of `ptr`?
         let tag = if let Some(borrow_tracker) = &ecx.machine.borrow_tracker {
-            borrow_tracker.borrow_mut().base_ptr_tag(alloc_id, &ecx.machine)
+            borrow_tracker.borrow_mut().root_ptr_tag(alloc_id, &ecx.machine)
         } else {
             // Value does not matter, SB is disabled
             BorTag::default()
         };
-        ecx.ptr_from_rel_ptr(ptr, tag)
+        ecx.adjust_alloc_root_pointer(ptr, tag, kind)
     }
 
     /// Called on `usize as ptr` casts.

tests/fail/both_borrows/invalidate_against_protector3.stack.stderr

@@ -6,7 +6,7 @@ LL |     unsafe { *x = 0 };
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
    = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
-help: <TAG> was created here, as the base tag for ALLOC
+help: <TAG> was created here, as the root tag for ALLOC
   --> $DIR/invalidate_against_protector3.rs:LL:CC
    |
 LL |         let ptr = alloc(Layout::for_value(&0i32)) as *mut i32;