Check if an object is in our heap before using VM map during counting live bytes (#1289)

This PR fixes a bug in `increase_live_bytes`. If an object in the VM
space is scanned, the method will be called with an object reference
into the VM space, which may not be in our heap range. Then we get a
space descriptor from the VM map, and we will see panics in the
following code.

https://github.com/mmtk/mmtk-core/blob/129362d4f39a1191562d276c42f5b03e52aa287a/src/util/heap/layout/map64.rs#L209

https://github.com/mmtk/mmtk-core/blob/129362d4f39a1191562d276c42f5b03e52aa287a/src/util/heap/layout/map32.rs#L258

This PR works around the problem by checking if the object is in our
heap range first.

Author: qinsoon

src/scheduler/worker.rs

@@ -71,15 +71,17 @@ impl<VM: VMBinding> GCWorkerShared<VM> {
         let bytes = VM::VMObjectModel::get_current_size(object);
         // Get the space index from descriptor
         let space_descriptor = VM_MAP.get_descriptor_for_address(object.to_raw_address());
-        let space_index = space_descriptor.get_index();
-        debug_assert!(
-            space_index < MAX_SPACES,
-            "Space index {} is not in the range of [0, {})",
-            space_index,
-            MAX_SPACES
-        );
-        // Accumulate the live bytes for the index
-        live_bytes_per_space[space_index] += bytes;
+        if space_descriptor != crate::util::heap::space_descriptor::SpaceDescriptor::UNINITIALIZED {
+            let space_index = space_descriptor.get_index();
+            debug_assert!(
+                space_index < MAX_SPACES,
+                "Space index {} is not in the range of [0, {})",
+                space_index,
+                MAX_SPACES
+            );
+            // Accumulate the live bytes for the index
+            live_bytes_per_space[space_index] += bytes;
+        }
     }
 }
 

src/util/heap/layout/map.rs

@@ -81,6 +81,8 @@ pub trait VMMap: Sync {
 
     fn is_finalized(&self) -> bool;
 
+    /// Get the space descriptor for the given address. Return SpaceDescriptor::UNINITIALIZED if the
+    /// address is not within the MMTk heap range, or not within MMTk spaces.
     fn get_descriptor_for_address(&self, address: Address) -> SpaceDescriptor;
 
     fn add_to_cumulative_committed_pages(&self, pages: usize);

src/util/heap/layout/map32.rs

@@ -255,7 +255,10 @@ impl VMMap for Map32 {
 
     fn get_descriptor_for_address(&self, address: Address) -> SpaceDescriptor {
         let index = address.chunk_index();
-        self.descriptor_map[index]
+        self.descriptor_map
+            .get(index)
+            .copied()
+            .unwrap_or(SpaceDescriptor::UNINITIALIZED)
     }
 
     fn add_to_cumulative_committed_pages(&self, pages: usize) {

src/util/heap/layout/map64.rs

@@ -206,8 +206,11 @@ impl VMMap for Map64 {
     }
 
     fn get_descriptor_for_address(&self, address: Address) -> SpaceDescriptor {
-        let index = Self::space_index(address).unwrap();
-        self.inner().descriptor_map[index]
+        if let Some(index) = Self::space_index(address) {
+            self.inner().descriptor_map[index]
+        } else {
+            SpaceDescriptor::UNINITIALIZED
+        }
     }
 
     fn add_to_cumulative_committed_pages(&self, pages: usize) {