fix init_allocation_extra

Author: RalfJung

src/librustc_mir/const_eval.rs

@@ -462,9 +462,9 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         _id: AllocId,
         alloc: Cow<'b, Allocation>,
         _kind: Option<MemoryKind<!>>,
-    ) -> Cow<'b, Allocation<Self::PointerTag>> {
+    ) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
         // We do not use a tag so we can just cheaply forward the allocation
-        alloc
+        (alloc, ())
     }
 
     #[inline(always)]

src/librustc_mir/interpret/eval_context.rs

@@ -251,9 +251,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     }
 
     /// Call this to turn untagged "global" pointers (obtained via `tcx`) into
-    /// the *canonical* machine pointer to the allocation. This represents a *direct*
-    /// access to that memory, as opposed to access through a pointer that was created
-    /// by the program. Must never be used for derived (program-created) pointers!
+    /// the *canonical* machine pointer to the allocation.  Must never be used
+    /// for any other pointers!
+    ///
+    /// This represents a *direct* access to that memory, as opposed to access
+    /// through a pointer that was created by the program.
     #[inline(always)]
     pub fn tag_static_base_pointer(&self, ptr: Pointer) -> Pointer<M::PointerTag> {
         self.memory.tag_static_base_pointer(ptr)

src/librustc_mir/interpret/machine.rs

@@ -240,18 +240,20 @@ pub trait Machine<'mir, 'tcx>: Sized {
     /// allocation (because a copy had to be done to add tags or metadata), machine memory will
     /// cache the result. (This relies on `AllocMap::get_or` being able to add the
     /// owned allocation to the map even when the map is shared.)
+    ///
+    /// Also return the "base" tag to use for this allocation: the one that is used for direct
+    /// accesses to this allocation. If `kind == STATIC_KIND`, this tag must be consistent
+    /// with `tag_static_base_pointer`.
     fn init_allocation_extra<'b>(
         memory_extra: &Self::MemoryExtra,
         id: AllocId,
         alloc: Cow<'b, Allocation>,
         kind: Option<MemoryKind<Self::MemoryKinds>>,
-    ) -> Cow<'b, Allocation<Self::PointerTag, Self::AllocExtra>>;
+    ) -> (Cow<'b, Allocation<Self::PointerTag, Self::AllocExtra>>, Self::PointerTag);
 
-    /// Return the "base" tag for the given static allocation: the one that is used for direct
-    /// accesses to this static/const/fn allocation.
-    ///
-    /// Be aware that requesting the `Allocation` for that `id` will lead to cycles
-    /// for cyclic statics!
+    /// Return the "base" tag for the given *static* allocation: the one that is used for direct
+    /// accesses to this static/const/fn allocation. If `id` is not a static allocation,
+    /// this will return an unusable tag (i.e., accesses will be UB)!
     fn tag_static_base_pointer(
         memory_extra: &Self::MemoryExtra,
         id: AllocId,

src/librustc_mir/interpret/memory.rs

@@ -144,9 +144,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
     }
 
     /// Call this to turn untagged "global" pointers (obtained via `tcx`) into
-    /// the *canonical* machine pointer to the allocation. This represents a *direct*
-    /// access to that memory, as opposed to access through a pointer that was created
-    /// by the program. Must never be used for derived (program-created) pointers!
+    /// the *canonical* machine pointer to the allocation.  Must never be used
+    /// for any other pointers!
+    ///
+    /// This represents a *direct* access to that memory, as opposed to access
+    /// through a pointer that was created by the program.
     #[inline]
     pub fn tag_static_base_pointer(&self, ptr: Pointer) -> Pointer<M::PointerTag> {
         ptr.with_tag(M::tag_static_base_pointer(&self.extra, ptr.alloc_id))
@@ -195,9 +197,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         kind: MemoryKind<M::MemoryKinds>,
     ) -> Pointer<M::PointerTag> {
         let id = self.tcx.alloc_map.lock().reserve();
-        let alloc = M::init_allocation_extra(&self.extra, id, Cow::Owned(alloc), Some(kind));
+        debug_assert_ne!(Some(kind), M::STATIC_KIND.map(MemoryKind::Machine),
+            "dynamically allocating static memory");
+        let (alloc, tag) = M::init_allocation_extra(&self.extra, id, Cow::Owned(alloc), Some(kind));
         self.alloc_map.insert(id, (kind, alloc.into_owned()));
-        self.tag_static_base_pointer(Pointer::from(id))
+        Pointer::from(id).with_tag(tag)
     }
 
     pub fn reallocate(
@@ -478,12 +482,14 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             }
         };
         // We got tcx memory. Let the machine initialize its "extra" stuff.
-        Ok(M::init_allocation_extra(
+        let (alloc, tag) = M::init_allocation_extra(
             memory_extra,
             id, // always use the ID we got as input, not the "hidden" one.
             alloc,
             M::STATIC_KIND.map(MemoryKind::Machine),
-        ))
+        );
+        debug_assert_eq!(tag, M::tag_static_base_pointer(memory_extra, id));
+        Ok(alloc)
     }
 
     /// Gives raw access to the `Allocation`, without bounds or alignment checks.

src/librustc_mir/transform/const_prop.rs

@@ -196,9 +196,9 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine {
         _id: AllocId,
         alloc: Cow<'b, Allocation>,
         _kind: Option<MemoryKind<!>>,
-    ) -> Cow<'b, Allocation<Self::PointerTag>> {
+    ) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
         // We do not use a tag so we can just cheaply forward the allocation
-        alloc
+        (alloc, ())
     }
 
     #[inline(always)]