Add a findObject function to CardTable for assertions in writer barri…

…ers (facebook#1513) Summary: Pull Request resolved: facebook#1513 Differential Revision: D62169632
lavenzg · Dec 10, 2024 · 2c636f5 · 2c636f5
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diff --git a/include/hermes/VM/CardTableNC.h b/include/hermes/VM/CardTableNC.h
@@ -278,6 +278,9 @@ class CardTable {
   ///
   /// \pre start is card-aligned.
   void verifyBoundaries(char *start, char *level) const;
+
+  /// Find the object that owns the memory at \p loc.
+  GCCell *findObjectContaining(const void *loc) const;
 #endif // HERMES_SLOW_DEBUG
 
  private:

diff --git a/lib/VM/gcs/CardTableNC.cpp b/lib/VM/gcs/CardTableNC.cpp
@@ -172,6 +172,13 @@ void CardTable::verifyBoundaries(char *start, char *level) const {
         "Card object boundary is broken: first obj doesn't extend into card");
   }
 }
+
+GCCell *CardTable::findObjectContaining(const void *loc) const {
+  GCCell *obj = firstObjForCard(addressToIndex(loc));
+  while (obj->nextCell() < loc)
+    obj = obj->nextCell();
+  return obj;
+}
 #endif // HERMES_SLOW_DEBUG
 
 } // namespace vm