Pattern match on generated code to find edge counters.

runtime/vm/code_patcher_ia32.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_IA32.
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/assembler.h"
 #include "vm/code_patcher.h"
 #include "vm/cpu.h"
@@ skipping 131 matching lines @@
   uword call_address() const {
     return start_;
   }
 
   uword start_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(StaticCall);
 };
 
 
-// The expected pattern of a dart closure call:
+// The expected pattern of a Dart closure call:
 //   mov EDX, arguments_descriptor_array
 //   call target_address
 //   <- return address
 class ClosureCall : public ValueObject {
  public:
   explicit ClosureCall(uword return_address)
       : start_(return_address - (kInstr1Size + kInstr2Size)) {
     ASSERT(IsValid(return_address));
     ASSERT(kInstr2Size == Assembler::kCallExternalLabelSize);
   }
@@ skipping 89 matching lines @@
     *ic_data_result = ic_data.raw();
   }
   return ic_data.GetTargetAt(0);
 }
 
 
 intptr_t CodePatcher::InstanceCallSizeInBytes() {
   return InstanceCall::kNumInstructions * InstanceCall::kInstructionSize;
 }
 
+
+// The expected code pattern of an edge counter in unoptimized code:
+//  b8 imm32    mov EAX, immediate
+class EdgeCounter : public ValueObject {
+ public:
+  EdgeCounter(uword pc, const Code& ignored) : end_(pc - kAdjust) {
+    ASSERT(IsValid(end_));
+  }
+
+  static bool IsValid(uword end) {
+    return (*reinterpret_cast<uint8_t*>(end - 5) == 0xb8);
+  }
+
+  RawObject* edge_counter() const {
+    return *reinterpret_cast<RawObject**>(end_ - 4);
+  }
+
+ private:
+  // The edge counter load is followed by the fixed-size edge counter
+  // incrementing code:
+  //     83 40 0b 02               add [eax+0xb],0x2
+  static const intptr_t kAdjust = 4;
+
+  uword end_;
+};
+
+
+RawObject* CodePatcher::GetEdgeCounterAt(uword pc, const Code& code) {
+  ASSERT(code.ContainsInstructionAt(pc));
+  EdgeCounter counter(pc, code);
+  return counter.edge_counter();
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32