Last snapshot bits to get working precompiled hello_world on x64.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index 3612f1c0c4f1184b39929a069aeace1930e16940..283b0456452a31cb60b0127d3ad3f6c0bb333d76 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -198,6 +198,8 @@ SnapshotReader::SnapshotReader(
       data_(ExternalTypedData::Handle(zone_)),
       typed_data_(TypedData::Handle(zone_)),
       code_(Code::Handle(zone_)),
+      function_(Function::Handle(zone_)),
+      megamorphic_cache_(MegamorphicCache::Handle(zone_)),
       error_(UnhandledException::Handle(zone_)),
       max_vm_isolate_object_id_(
           (kind == Snapshot::kFull) ?
@@ -1173,9 +1175,18 @@ void InstructionsWriter::WriteAssembly() {
 
   stream_.Print(".text\n");
   stream_.Print(".globl _kInstructionsSnapshot\n");
-  stream_.Print(".balign %" Pd ", 0\n", OS::PreferredCodeAlignment());
+  stream_.Print(".balign %" Pd ", 0\n", OS::kMaxPreferredCodeAlignment);
   stream_.Print("_kInstructionsSnapshot:\n");
 
+  // This head also provides the gap to make the instructions snapshot
+  // look like a HeapPage.
+  intptr_t instructions_length = next_offset_;
+  WriteWordLiteral(instructions_length);
+  intptr_t header_words = HeaderSize() / sizeof(uword);
+  for (intptr_t i = 1; i < header_words; i++) {
+    WriteWordLiteral(0);
+  }
+
   Object& owner = Object::Handle(Z);
   String& str = String::Handle(Z);
 
@@ -1188,16 +1199,25 @@ void InstructionsWriter::WriteAssembly() {
     {
       // 1. Write from the header to the entry point.
       NoSafepointScope no_safepoint;
-      uword beginning = reinterpret_cast<uword>(insns.raw()) - kHeapObjectTag;
+
+      uword beginning = reinterpret_cast<uword>(insns.raw_ptr());
       uword entry = beginning + Instructions::HeaderSize();
 
       ASSERT(Utils::IsAligned(beginning, sizeof(uint64_t)));
       ASSERT(Utils::IsAligned(entry, sizeof(uint64_t)));
 
-      for (uint64_t* cursor = reinterpret_cast<uint64_t*>(beginning);
-           cursor < reinterpret_cast<uint64_t*>(entry);
+      // Write Instructions with the mark and VM heap bits set.
+      uword marked_tags = insns.raw_ptr()->tags_;
+      marked_tags = RawObject::VMHeapObjectTag::update(true, marked_tags);
+      marked_tags = RawObject::MarkBit::update(true, marked_tags);
+
+      WriteWordLiteral(marked_tags);
+      beginning += sizeof(uword);
+
+      for (uword* cursor = reinterpret_cast<uword*>(beginning);
+           cursor < reinterpret_cast<uword*>(entry);
            cursor++) {
-        stream_.Print(".quad 0x%0.16" Px64 "\n", *cursor);
+        WriteWordLiteral(*cursor);
       }
     }
 
@@ -1230,10 +1250,10 @@ void InstructionsWriter::WriteAssembly() {
       ASSERT(Utils::IsAligned(entry, sizeof(uint64_t)));
       ASSERT(Utils::IsAligned(end, sizeof(uint64_t)));
 
-      for (uint64_t* cursor = reinterpret_cast<uint64_t*>(entry);
-           cursor < reinterpret_cast<uint64_t*>(end);
+      for (uword* cursor = reinterpret_cast<uword*>(entry);
+           cursor < reinterpret_cast<uword*>(end);
            cursor++) {
-        stream_.Print(".quad 0x%0.16" Px64 "\n", *cursor);
+        WriteWordLiteral(*cursor);
       }
     }
   }
@@ -1255,9 +1275,9 @@ RawInstructions* InstructionsReader::GetInstructionsAt(int32_t offset,
            actual_tags);
   }
 
-  // TODO(rmacnak): The above contains stale pointers to a Code and an
-  // ObjectPool. Return the actual result after calling convention change.
-  return Instructions::null();
+  ASSERT(result->IsMarked());
+
+  return result;
 }