From 2c636f541e63a0182dce7edf0c04a2c63e45f474 Mon Sep 17 00:00:00 2001
From: Gang Zhao <zhaogang@meta.com>
Date: Mon, 9 Dec 2024 17:13:35 -0800
Subject: [PATCH] Add a findObject function to CardTable for assertions in
 writer barriers (#1513)

Summary: Pull Request resolved: https://github.com/facebook/hermes/pull/1513

Differential Revision: D62169632
---
 include/hermes/VM/CardTableNC.h | 3 +++
 lib/VM/gcs/CardTableNC.cpp      | 7 +++++++
 2 files changed, 10 insertions(+)

diff --git a/include/hermes/VM/CardTableNC.h b/include/hermes/VM/CardTableNC.h
index 7bce327636a..6881873e7b8 100644
--- 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
index 10937e15192..018ff2c5a06 100644
--- 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