Last snapshot bits to get working precompiled hello_world on x64.

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 379287a67b4f94a77a36c0263c45cb0529b70d12..ed654ee467bdd22846484189225af3536fe2deb0 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -880,6 +880,24 @@ uword Isolate::GetCurrentStackPointer() {
 }
 
 
+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);