Fix for 3303 MultithreadedParallelIsolates has a race condition.

src/arm64/macro-assembler-arm64.cc

Index: src/arm64/macro-assembler-arm64.cc
diff --git a/src/arm64/macro-assembler-arm64.cc b/src/arm64/macro-assembler-arm64.cc
index 0b2954e18f54ee9b78eeb5b6ff3a517e62b5876e..cce03af879de9b4b7aabedddfc996957b81c378e 100644
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -5020,7 +5020,8 @@ void MacroAssembler::EmitFrameSetupForCodeAgePatching() {
   // TODO(jbramley): Other architectures use the internal memcpy to copy the
   // sequence. If this is a performance bottleneck, we should consider caching
   // the sequence and copying it in the same way.
-  InstructionAccurateScope scope(this, kCodeAgeSequenceSize / kInstructionSize);
+  InstructionAccurateScope scope(this,
+                                 kNoCodeAgeSequenceLength / kInstructionSize);
   ASSERT(jssp.Is(StackPointer()));
   EmitFrameSetupForCodeAgePatching(this);
 }
@@ -5028,7 +5029,8 @@ void MacroAssembler::EmitFrameSetupForCodeAgePatching() {
 
 
 void MacroAssembler::EmitCodeAgeSequence(Code* stub) {
-  InstructionAccurateScope scope(this, kCodeAgeSequenceSize / kInstructionSize);
+  InstructionAccurateScope scope(this,
+                                 kNoCodeAgeSequenceLength / kInstructionSize);
   ASSERT(jssp.Is(StackPointer()));
   EmitCodeAgeSequence(this, stub);
 }
@@ -5052,7 +5054,7 @@ void MacroAssembler::EmitFrameSetupForCodeAgePatching(Assembler * assm) {
   __ stp(fp, lr, MemOperand(jssp, 2 * kXRegSize));
   __ add(fp, jssp, StandardFrameConstants::kFixedFrameSizeFromFp);
 
-  __ AssertSizeOfCodeGeneratedSince(&start, kCodeAgeSequenceSize);
+  __ AssertSizeOfCodeGeneratedSince(&start, kNoCodeAgeSequenceLength);
 }
 
 
@@ -5075,25 +5077,13 @@ void MacroAssembler::EmitCodeAgeSequence(Assembler * assm,
   __ AssertSizeOfCodeGeneratedSince(&start, kCodeAgeStubEntryOffset);
   if (stub) {
     __ dc64(reinterpret_cast<uint64_t>(stub->instruction_start()));
-    __ AssertSizeOfCodeGeneratedSince(&start, kCodeAgeSequenceSize);
+    __ AssertSizeOfCodeGeneratedSince(&start, kNoCodeAgeSequenceLength);
   }
 }
 
 
-bool MacroAssembler::IsYoungSequence(byte* sequence) {
-  // Generate a young sequence to compare with.
-  const int length = kCodeAgeSequenceSize / kInstructionSize;
-  static bool initialized = false;
-  static byte young[kCodeAgeSequenceSize];
-  if (!initialized) {
-    PatchingAssembler patcher(young, length);
-    // The young sequence is the frame setup code for FUNCTION code types. It is
-    // generated by FullCodeGenerator::Generate.
-    MacroAssembler::EmitFrameSetupForCodeAgePatching(&patcher);
-    initialized = true;
-  }
-
-  bool is_young = (memcmp(sequence, young, kCodeAgeSequenceSize) == 0);
+bool MacroAssembler::IsYoungSequence(Isolate* isolate, byte* sequence) {
+  bool is_young = isolate->no_code_age_sequence()->Match(sequence);
   ASSERT(is_young || IsCodeAgeSequence(sequence));
   return is_young;
 }
@@ -5107,6 +5097,7 @@ bool MacroAssembler::IsCodeAgeSequence(byte* sequence) {
   const int length = kCodeAgeStubEntryOffset / kInstructionSize;
   static bool initialized = false;
   static byte old[kCodeAgeStubEntryOffset];
+  // TODO(mvstanton): this static isn't thread safe.

[Sven Panne, 2014/05/05 07:54:14]

Perhaps NoCodeAgeSequence should have a more generic name and be used here, too?

[mvstanton, 2014/05/06 09:55:45]

I changed it to CodeAgingHelper, and it can determine if your code is old or
young, this addressed the thread safety issue too.

   if (!initialized) {
     PatchingAssembler patcher(old, length);
     MacroAssembler::EmitCodeAgeSequence(&patcher, NULL);