Fix for 3303 MultithreadedParallelIsolates has a race condition.

src/arm64/macro-assembler-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "v8.h"
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "bootstrapper.h"
 #include "codegen.h"
@@ skipping 5002 matching lines @@
 
   TmpList()->set_list(old_tmp_list);
   FPTmpList()->set_list(old_fp_tmp_list);
 }
 
 
 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);
 }
 
 
 
 void MacroAssembler::EmitCodeAgeSequence(Code* stub) {
-  InstructionAccurateScope scope(this, kCodeAgeSequenceSize / kInstructionSize);
+  InstructionAccurateScope scope(this,
+                                 kNoCodeAgeSequenceLength / kInstructionSize);
   ASSERT(jssp.Is(StackPointer()));
   EmitCodeAgeSequence(this, stub);
 }
 
 
 #undef __
 #define __ assm->
 
 
 void MacroAssembler::EmitFrameSetupForCodeAgePatching(Assembler * assm) {
   Label start;
   __ bind(&start);
 
   // We can do this sequence using four instructions, but the code ageing
   // sequence that patches it needs five, so we use the extra space to try to
   // simplify some addressing modes and remove some dependencies (compared to
   // using two stp instructions with write-back).
   __ sub(jssp, jssp, 4 * kXRegSize);
   __ sub(csp, csp, 4 * kXRegSize);
   __ stp(x1, cp, MemOperand(jssp, 0 * kXRegSize));
   __ stp(fp, lr, MemOperand(jssp, 2 * kXRegSize));
   __ add(fp, jssp, StandardFrameConstants::kFixedFrameSizeFromFp);
 
-  __ AssertSizeOfCodeGeneratedSince(&start, kCodeAgeSequenceSize);
+  __ AssertSizeOfCodeGeneratedSince(&start, kNoCodeAgeSequenceLength);
 }
 
 
 void MacroAssembler::EmitCodeAgeSequence(Assembler * assm,
                                          Code * stub) {
   Label start;
   __ bind(&start);
   // When the stub is called, the sequence is replaced with the young sequence
   // (as in EmitFrameSetupForCodeAgePatching). After the code is replaced, the
   // stub jumps to &start, stored in x0. The young sequence does not call the
   // stub so there is no infinite loop here.
   //
   // A branch (br) is used rather than a call (blr) because this code replaces
   // the frame setup code that would normally preserve lr.
   __ LoadLiteral(ip0, kCodeAgeStubEntryOffset);
   __ adr(x0, &start);
   __ br(ip0);
   // IsCodeAgeSequence in codegen-arm64.cc assumes that the code generated up
   // until now (kCodeAgeStubEntryOffset) is the same for all code age sequences.
   __ 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;
 }
 
 
 #ifdef DEBUG
 bool MacroAssembler::IsCodeAgeSequence(byte* sequence) {
   // The old sequence varies depending on the code age. However, the code up
   // until kCodeAgeStubEntryOffset does not change, so we can check that part to
   // get a reasonable level of verification.
   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);
     initialized = true;
   }
   return memcmp(sequence, old, kCodeAgeStubEntryOffset) == 0;
 }
 #endif
 
 
@@ skipping 95 matching lines @@
   }
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64