Write barrier audit: Verify previous value in generated code.

runtime/vm/assembler_ia32.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ASSEMBLER_IA32_H_
 #define VM_ASSEMBLER_IA32_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_ia32.h directly; use assembler.h instead.
 #endif
@@ skipping 608 matching lines @@
   void leave();
 
   void ret();
   void ret(const Immediate& imm);
 
   // 'size' indicates size in bytes and must be in the range 1..8.
   void nop(int size = 1);
   void int3();
   void hlt();
 
+  // Note: verified_mem mode forces far jumps.
   void j(Condition condition, Label* label, bool near = kFarJump);
   void j(Condition condition, const ExternalLabel* label);
 
   void jmp(Register reg);
+  // Note: verified_mem mode forces far jumps.
   void jmp(Label* label, bool near = kFarJump);
   void jmp(const ExternalLabel* label);
 
   void lock();
   void cmpxchgl(const Address& address, Register reg);
 
   void cpuid();
 
   /*
    * Macros for High-level operations and implemented on all architectures.
@@ skipping 279 matching lines @@
   void EmitGenericShift(int rm, Register reg, const Immediate& imm);
   void EmitGenericShift(int rm, const Operand& operand, Register shifter);
 
   void StoreIntoObjectFilter(Register object, Register value, Label* no_update);
 
   // Shorter filtering sequence that assumes that value is not a smi.
   void StoreIntoObjectFilterNoSmi(Register object,
                                   Register value,
                                   Label* no_update);
 
-  // Private helpers for write barrier verification.
+  // Analogous to VerifiedMemory::Verify(address, kWordSize).
+  void VerifyHeapWord(const Address& address);
+  // Analogous to VerifiedMemory::Write.
   void VerifiedWrite(const Address& dest, Register value);
   void UnverifiedStoreOldObject(const Address& dest, const Object& value);
 
   int32_t jit_cookie();
 
   AssemblerBuffer buffer_;
   GrowableObjectArray& object_pool_;  // Object pool is not used on ia32.
   intptr_t prologue_offset_;
   int32_t jit_cookie_;
   GrowableArray<CodeComment*> comments_;
@@ skipping 29 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_IA32_H_