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/runtime/arch/arm/quick_entrypoints_arm.S b/runtime/arch/arm/quick_entrypoints_arm.S
index 736ce2f..c11349802 100644
--- a/runtime/arch/arm/quick_entrypoints_arm.S
+++ b/runtime/arch/arm/quick_entrypoints_arm.S
@@ -325,24 +325,25 @@
ENTRY art_quick_lock_object
cbz r0, slow_lock
retry_lock:
- ldrex r1, [r0, #LOCK_WORD_OFFSET]
ldrt r2, [r9, #THREAD_ID_OFFSET]
- cmp r1, #0
- bmi slow_lock @ lock word contains a monitor
- bne already_thin
+ ldrex r1, [r0, #LOCK_WORD_OFFSET]
+ cbnz r1, not_unlocked @ already thin locked
@ unlocked case - r2 holds thread id with count of 0
strex r3, r2, [r0, #LOCK_WORD_OFFSET]
cbnz r3, strex_fail @ store failed, retry
bx lr
strex_fail:
b retry_lock @ unlikely forward branch, need to reload and recheck r1/r2
-already_thin:
+not_unlocked:
+ lsr r3, r1, 30
+ cbnz r3, slow_lock @ if either of the top two bits are set, go slow path
eor r2, r1, r2 @ lock_word.ThreadId() ^ self->ThreadId()
uxth r2, r2 @ zero top 16 bits
cbnz r2, slow_lock @ lock word and self thread id's match -> recursive lock
@ else contention, go to slow path
- adds r2, r1, #65536 @ increment count in lock word placing in r2 for storing
- bmi slow_lock @ if we overflow the count go slow
+ add r2, r1, #65536 @ increment count in lock word placing in r2 for storing
+ lsr r1, r2, 30 @ if either of the top two bits are set, we overflowed.
+ cbnz r1, slow_lock @ if we overflow the count go slow path
str r2, [r0, #LOCK_WORD_OFFSET] @ no need for strex as we hold the lock
bx lr
slow_lock:
@@ -363,9 +364,9 @@
ENTRY art_quick_unlock_object
cbz r0, slow_unlock
ldr r1, [r0, #LOCK_WORD_OFFSET]
+ lsr r2, r1, 30
+ cbnz r2, slow_unlock @ if either of the top two bits are set, go slow path
ldr r2, [r9, #THREAD_ID_OFFSET]
- cmp r1, #0
- bmi slow_unlock @ lock word contains a monitor
eor r3, r1, r2 @ lock_word.ThreadId() ^ self->ThreadId()
uxth r3, r3 @ zero top 16 bits
cbnz r3, slow_unlock @ do lock word and self thread id's match?