Fix races related to dex caches in runtime app images.

- Make sure dex cache arrays are properly aligned.
- Handle dex cache arrays being concurrently cleared when loading an
  image.
- Don't use memcpy but update entries one by one when generating the
  image.

Test: test.py
Bug: 260557058
Change-Id: I5ef72a7363fe5e108f62d03caa399e5300cf7a55

1 files changed, 17 insertions, 6 deletions

diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index b00910fec8..8927c4337e 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -1587,12 +1587,15 @@ static void VisitInternedStringReferences(
     if (obj_ptr->IsDexCache() && raw_member_offset >= sizeof(mirror::DexCache)) {
       // Special case for strings referenced from dex cache array.
       uint32_t offset = raw_member_offset - sizeof(mirror::DexCache);
-      ObjPtr<mirror::String> referred_string =
-          obj_ptr->AsDexCache()->GetStringsArray()->Get(offset);
-      DCHECK(referred_string != nullptr);
-      ObjPtr<mirror::String> visited = visitor(referred_string);
-      if (visited != referred_string) {
-        obj_ptr->AsDexCache()->GetStringsArray()->Set(offset, visited.Ptr());
+      mirror::GcRootArray<mirror::String>* array = obj_ptr->AsDexCache()->GetStringsArray();
+      // The array could be concurrently set to null. See `StartupCompletedTask`.
+      if (array != nullptr) {
+        ObjPtr<mirror::String> referred_string = array->Get(offset);
+        DCHECK(referred_string != nullptr);
+        ObjPtr<mirror::String> visited = visitor(referred_string);
+        if (visited != referred_string) {
+          obj_ptr->AsDexCache()->GetStringsArray()->Set(offset, visited.Ptr());
+        }
       }
     } else {
       DCHECK_ALIGNED(raw_member_offset, 2);
@@ -1705,6 +1708,14 @@ void AppImageLoadingHelper::Update(
       }
     }, space->Begin(), kRuntimePointerSize);
   }
+
+  if (runtime->GetStartupCompleted()) {
+    // Free up dex cache arrays that we would only allocate at startup.
+    for (auto dex_cache : dex_caches.Iterate<mirror::DexCache>()) {
+      dex_cache->UnlinkStartupCaches();
+    }
+    space->ReleaseMetadata();
+  }
 }
 
 void AppImageLoadingHelper::HandleAppImageStrings(gc::space::ImageSpace* space) {