Track prologue offset of Code and use for more precise return addresses

runtime/vm/assembler.h

 // 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.
 
 #ifndef VM_ASSEMBLER_H_
 #define VM_ASSEMBLER_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/globals.h"
@@ skipping 71 matching lines @@
     ASSERT(HasEnsuredCapacity());
     *reinterpret_cast<T*>(cursor_) = value;
     cursor_ += sizeof(T);
   }
 
   template<typename T> void Remit() {
     ASSERT(Size() >= static_cast<intptr_t>(sizeof(T)));
     cursor_ -= sizeof(T);
   }
 
+  // Return address to code at |position| bytes.
+  uword Address(intptr_t position) {
+    return reinterpret_cast<uword>(contents_ + position);
+  }
+
   template<typename T> T Load(intptr_t position) {
     ASSERT(position >= 0 &&
            position <= (Size() - static_cast<intptr_t>(sizeof(T))));
     return *reinterpret_cast<T*>(contents_ + position);
   }
 
   template<typename T> void Store(intptr_t position, T value) {
     ASSERT(position >= 0 &&
            position <= (Size() - static_cast<intptr_t>(sizeof(T))));
     *reinterpret_cast<T*>(contents_ + position) = value;
@@ skipping 197 matching lines @@
 #include "vm/assembler_arm.h"
 #elif defined(TARGET_ARCH_ARM64)
 #include "vm/assembler_arm64.h"
 #elif defined(TARGET_ARCH_MIPS)
 #include "vm/assembler_mips.h"
 #else
 #error Unknown architecture.
 #endif
 
 #endif  // VM_ASSEMBLER_H_