- Make sure to be able to deal with unaligned snapshot buffers

runtime/vm/snapshot.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_SNAPSHOT_H_
 #define VM_SNAPSHOT_H_
 
 #include "platform/assert.h"
+#include "platform/utils.h"
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
 #include "vm/datastream.h"
 #include "vm/exceptions.h"
 #include "vm/globals.h"
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
 #include "vm/visitor.h"
 
 namespace dart {
@@ skipping 116 matching lines @@
   };
 
   static const int kHeaderSize = 2 * sizeof(int64_t);
   static const int kLengthIndex = 0;
   static const int kSnapshotFlagIndex = 1;
 
   static const Snapshot* SetupFromBuffer(const void* raw_memory);
 
   // Getters.
   const uint8_t* content() const { return content_; }
-  intptr_t length() const { return static_cast<intptr_t>(length_); }
-  Kind kind() const { return static_cast<Kind>(kind_); }
+  intptr_t length() const {
+    return static_cast<intptr_t>(ReadUnaligned(&unaligned_length_));
+  }
+  Kind kind() const {
+    return static_cast<Kind>(ReadUnaligned(&unaligned_kind_));
+  }
 
-  bool IsMessageSnapshot() const { return kind_ == kMessage; }
-  bool IsScriptSnapshot() const { return kind_ == kScript; }
-  bool IsFullSnapshot() const { return kind_ == kFull; }
+  bool IsMessageSnapshot() const { return kind() == kMessage; }
+  bool IsScriptSnapshot() const { return kind() == kScript; }
+  bool IsFullSnapshot() const { return kind() == kFull; }
   uint8_t* Addr() { return reinterpret_cast<uint8_t*>(this); }
 
-  static intptr_t length_offset() { return OFFSET_OF(Snapshot, length_); }
+  static intptr_t length_offset() {
+    return OFFSET_OF(Snapshot, unaligned_length_);
+  }
   static intptr_t kind_offset() {
-    return OFFSET_OF(Snapshot, kind_);
+    return OFFSET_OF(Snapshot, unaligned_kind_);
   }
 
  private:
-  Snapshot() : length_(0), kind_(kFull) {}
+  // Prevent Snapshot from ever being allocated directly.
+  Snapshot();
 
-  int64_t length_;  // Stream length.
-  int64_t kind_;  // Kind of snapshot.
+  // The following fields are potentially unaligned.
+  int64_t unaligned_length_;  // Stream length.
+  int64_t unaligned_kind_;  // Kind of snapshot.
   uint8_t content_[];  // Stream content.
 
   DISALLOW_COPY_AND_ASSIGN(Snapshot);
 };
 
 
 class BaseReader {
  public:
   BaseReader(const uint8_t* buffer, intptr_t size) : stream_(buffer, size) {}
   // Reads raw data (for basic types).
@@ skipping 532 matching lines @@
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_SNAPSHOT_H_