Last snapshot bits to get working precompiled hello_world on x64.

runtime/vm/isolate.cc

 // 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.
 
 #include "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/json.h"
 #include "vm/code_observers.h"
@@ skipping 862 matching lines @@
   uword stack_allocated_local_address = reinterpret_cast<uword>(&func);
   return stack_allocated_local_address;
 #endif
 #else
   uword stack_allocated_local_address = reinterpret_cast<uword>(&func);
   return stack_allocated_local_address;
 #endif
 }
 
 
+void Isolate::SetupInstructionsSnapshotPage(
+    const uint8_t* instructions_snapshot) {
+  // First word is the size of the snapshot, including the header.
+  uword header_size = OS::kMaxPreferredCodeAlignment;
+  uword snapshot_size = static_cast<uword>(
+      *reinterpret_cast<const uword*>(instructions_snapshot));
+  uword instructions_size = snapshot_size - header_size;
+  void* instructions_start = reinterpret_cast<void*>(
+      reinterpret_cast<uword>(instructions_snapshot) + header_size);

[siva, 2015/09/15 23:22:01]

As discussed offline it might be more readable to define a class
InsrtuctionSnapshot and have accessors length() and context() similar to the
regular Snapshot class.

You could move the header_size stuff also into that class.

+#if defined(DEBUG)
+  OS::Print("Precompiled instructions are at [%" Px ", %" Px ")\n",
+            reinterpret_cast<uword>(instructions_start),
+            reinterpret_cast<uword>(instructions_start) + instructions_size);
+#endif
+  heap_->SetupInstructionsSnapshotPage(instructions_start, instructions_size);
+}
+
+
 void Isolate::set_debugger_name(const char* name) {
   free(debugger_name_);
   debugger_name_ = strdup(name);
 }
 
 
 void Isolate::BuildName(const char* name_prefix) {
   ASSERT(name_ == NULL);
   if (name_prefix == NULL) {
     name_prefix = "isolate";
@@ skipping 1453 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart