Fix object identity hash.
The object identity hash is now stored in the monitor word after
being computed. Hashes are computed by a pseudo random number
generator.
When we write the image, we eagerly compute object hashes to
prevent pages getting dirtied.
Bug: 8981901
Change-Id: Ic8edacbacb0afc7055fd740a52444929f88ed564
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index 871cfd5..d60b544 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -36,6 +36,7 @@
#include "globals.h"
#include "image.h"
#include "intern_table.h"
+#include "lock_word.h"
#include "mirror/art_field-inl.h"
#include "mirror/art_method-inl.h"
#include "mirror/array-inl.h"
@@ -489,7 +490,30 @@
DCHECK_LT(offset + n, image_writer->image_->Size());
memcpy(dst, src, n);
Object* copy = reinterpret_cast<Object*>(dst);
- copy->SetField32(Object::MonitorOffset(), 0, false); // We may have inflated the lock during compilation.
+ // Write in a hash code of objects which have inflated monitors or a hash code in their monitor
+ // word.
+ LockWord lw(copy->GetLockWord());
+ switch (lw.GetState()) {
+ case LockWord::kFatLocked: {
+ Monitor* monitor = lw.FatLockMonitor();
+ CHECK(monitor != nullptr);
+ CHECK(!monitor->IsLocked());
+ copy->SetLockWord(LockWord::FromHashCode(monitor->GetHashCode()));
+ break;
+ }
+ case LockWord::kThinLocked: {
+ LOG(FATAL) << "Thin locked object " << obj << " found during object copy";
+ break;
+ }
+ case LockWord::kUnlocked:
+ // Fall-through.
+ case LockWord::kHashCode:
+ // Do nothing since we can just keep the same hash code.
+ break;
+ default:
+ LOG(FATAL) << "Unreachable.";
+ break;
+ }
image_writer->FixupObject(obj, copy);
}