[ptr-compr] Fix decompression functions in v8-internal.h

jakobkummerow · Commit Bot · commit 8738ab802784 · 2020-02-13T12:30:25.000Z
In the final version of our pointer compression scheme, decompression uses zero-extension of the compressed value. The API copy of that code erroneously still used a sign-extending decompression from an earlier iteration of the scheme. Bug: v8:9706, v8:10198 Change-Id: I17c3a52d26ce26bc0623627d725f686c379fbd6e Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2051954 Commit-Queue: Jakob Kummerow <jkummerow@chromium.org> Reviewed-by: Ulan Degenbaev <ulan@chromium.org> Reviewed-by: Igor Sheludko <ishell@chromium.org> Cr-Commit-Position: refs/heads/master@{#66256}
diff --git a/include/v8-internal.h b/include/v8-internal.h
@@ -308,9 +308,9 @@ class Internals {
   V8_INLINE static internal::Address ReadTaggedPointerField(
       internal::Address heap_object_ptr, int offset) {
 #ifdef V8_COMPRESS_POINTERS
-    int32_t value = ReadRawField<int32_t>(heap_object_ptr, offset);
+    uint32_t value = ReadRawField<uint32_t>(heap_object_ptr, offset);
     internal::Address root = GetRootFromOnHeapAddress(heap_object_ptr);
-    return root + static_cast<internal::Address>(static_cast<intptr_t>(value));
+    return root + static_cast<internal::Address>(static_cast<uintptr_t>(value));
 #else
     return ReadRawField<internal::Address>(heap_object_ptr, offset);
 #endif
@@ -319,8 +319,8 @@ class Internals {
   V8_INLINE static internal::Address ReadTaggedSignedField(
       internal::Address heap_object_ptr, int offset) {
 #ifdef V8_COMPRESS_POINTERS
-    int32_t value = ReadRawField<int32_t>(heap_object_ptr, offset);
-    return static_cast<internal::Address>(static_cast<intptr_t>(value));
+    uint32_t value = ReadRawField<uint32_t>(heap_object_ptr, offset);
+    return static_cast<internal::Address>(static_cast<uintptr_t>(value));
 #else
     return ReadRawField<internal::Address>(heap_object_ptr, offset);
 #endif
@@ -337,13 +337,9 @@ class Internals {
   }
 
   V8_INLINE static internal::Address DecompressTaggedAnyField(
-      internal::Address heap_object_ptr, int32_t value) {
-    internal::Address root_mask = static_cast<internal::Address>(
-        -static_cast<intptr_t>(value & kSmiTagMask));
-    internal::Address root_or_zero =
-        root_mask & GetRootFromOnHeapAddress(heap_object_ptr);
-    return root_or_zero +
-           static_cast<internal::Address>(static_cast<intptr_t>(value));
+      internal::Address heap_object_ptr, uint32_t value) {
+    internal::Address root = GetRootFromOnHeapAddress(heap_object_ptr);
+    return root + static_cast<internal::Address>(static_cast<uintptr_t>(value));
   }
 #endif  // V8_COMPRESS_POINTERS
 };
diff --git a/include/v8.h b/include/v8.h
@@ -11239,7 +11239,7 @@ Local<Value> Object::GetInternalField(int index) {
 #ifdef V8_COMPRESS_POINTERS
     // We read the full pointer value and then decompress it in order to avoid
     // dealing with potential endiannes issues.
-    value = I::DecompressTaggedAnyField(obj, static_cast<int32_t>(value));
+    value = I::DecompressTaggedAnyField(obj, static_cast<uint32_t>(value));
 #endif
     internal::Isolate* isolate =
         internal::IsolateFromNeverReadOnlySpaceObject(obj);
@@ -11883,7 +11883,7 @@ Local<Value> Context::GetEmbedderData(int index) {
   // We read the full pointer value and then decompress it in order to avoid
   // dealing with potential endiannes issues.
   value =
-      I::DecompressTaggedAnyField(embedder_data, static_cast<int32_t>(value));
+      I::DecompressTaggedAnyField(embedder_data, static_cast<uint32_t>(value));
 #endif
   internal::Isolate* isolate = internal::IsolateFromNeverReadOnlySpaceObject(
       *reinterpret_cast<A*>(this));
