Orthogonalize the byte codes used for the snapshot so that

the issue of how the pointee is found and how the pointer
is encoded are separated out.  This will make it simpler to
support various pointers from and to code in the future.
Review URL: http://codereview.chromium.org/2069013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4687 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/assembler-arm.cc

@@ -108,6 +108,15 @@ void CpuFeatures::Probe() {
 const int RelocInfo::kApplyMask = 0;
 
 
+bool RelocInfo::IsCodedSpecially() {
+  // The deserializer needs to know whether a pointer is specially coded.  Being
+  // specially coded on ARM means that it is a movw/movt instruction.  We don't
+  // generate those yet.
+  return false;
+}
+
+
+
 void RelocInfo::PatchCode(byte* instructions, int instruction_count) {
   // Patch the code at the current address with the supplied instructions.
   Instr* pc = reinterpret_cast<Instr*>(pc_);

src/assembler.h

@@ -184,6 +184,11 @@ class RelocInfo BASE_EMBEDDED {
   // Apply a relocation by delta bytes
   INLINE(void apply(intptr_t delta));
 
+  // Is the pointer this relocation info refers to coded like a plain pointer
+  // or is it strange in some way (eg relative or patched into a series of
+  // instructions).
+  bool IsCodedSpecially();
+
   // Read/modify the code target in the branch/call instruction
   // this relocation applies to;
   // can only be called if IsCodeTarget(rmode_) || rmode_ == RUNTIME_ENTRY

src/ia32/assembler-ia32.cc

@@ -162,6 +162,15 @@ const int RelocInfo::kApplyMask =
     1 << RelocInfo::JS_RETURN | 1 << RelocInfo::INTERNAL_REFERENCE;
 
 
+bool RelocInfo::IsCodedSpecially() {
+  // The deserializer needs to know whether a pointer is specially coded.  Being
+  // specially coded on IA32 means that it is a relative address, as used by
+  // branch instructions.  These are also the ones that need changing when a
+  // code object moves.
+  return (1 << rmode_) & kApplyMask;
+}
+
+
 void RelocInfo::PatchCode(byte* instructions, int instruction_count) {
   // Patch the code at the current address with the supplied instructions.
   for (int i = 0; i < instruction_count; i++) {

src/serialize.h

@@ -137,17 +137,23 @@ class SnapshotByteSource {
 };
 
 
-// It is very common to have a reference to the object at word 10 in space 2,
-// the object at word 5 in space 2 and the object at word 28 in space 4.  This
-// only works for objects in the first page of a space.
-#define COMMON_REFERENCE_PATTERNS(f)                              \
-  f(kNumberOfSpaces, 2, 10)                                       \
-  f(kNumberOfSpaces + 1, 2, 5)                                    \
-  f(kNumberOfSpaces + 2, 4, 28)                                   \
-  f(kNumberOfSpaces + 3, 2, 21)                                   \
-  f(kNumberOfSpaces + 4, 2, 98)                                   \
-  f(kNumberOfSpaces + 5, 2, 67)                                   \
-  f(kNumberOfSpaces + 6, 4, 132)
+// It is very common to have a reference to objects at certain offsets in the
+// heap.  These offsets have been determined experimentally.  We code
+// references to such objects in a single byte that encodes the way the pointer
+// is written (only plain pointers allowed), the space number and the offset.
+// This only works for objects in the first page of a space.  Don't use this for
+// things in newspace since it bypasses the write barrier.
+
+static const int k64 = (sizeof(uintptr_t) - 4) / 4;
+
+#define COMMON_REFERENCE_PATTERNS(f)                               \
+  f(kNumberOfSpaces, 2, 11 - k64)                                  \
+  f(kNumberOfSpaces + 1, 2, 0)                                     \
+  f(kNumberOfSpaces + 2, 2, 142 - 16 * k64)                        \
+  f(kNumberOfSpaces + 3, 2, 74 - 15 * k64)                         \
+  f(kNumberOfSpaces + 4, 2, 5)                                     \
+  f(kNumberOfSpaces + 5, 1, 135)                                   \
+  f(kNumberOfSpaces + 6, 2, 228 - 39 * k64)
 
 #define COMMON_RAW_LENGTHS(f)        \
   f(1, 1)  \
@@ -175,37 +181,63 @@ class SerializerDeserializer: public ObjectVisitor {
   static void SetSnapshotCacheSize(int size);
 
  protected:
-  enum DataType {
-    RAW_DATA_SERIALIZATION = 0,
-    // And 15 common raw lengths.
-    OBJECT_SERIALIZATION = 16,
-    // One variant per space.
-    CODE_OBJECT_SERIALIZATION = 25,
-    // One per space (only code spaces in use).
-    EXTERNAL_REFERENCE_SERIALIZATION = 34,
-    EXTERNAL_BRANCH_TARGET_SERIALIZATION = 35,
-    SYNCHRONIZE = 36,
-    START_NEW_PAGE_SERIALIZATION = 37,
-    NATIVES_STRING_RESOURCE = 38,
-    ROOT_SERIALIZATION = 39,
-    PARTIAL_SNAPSHOT_CACHE_ENTRY = 40,
-    // Free: 41-47.
-    BACKREF_SERIALIZATION = 48,
-    // One per space, must be kSpaceMask aligned.
-    // Free: 57-63.
-    REFERENCE_SERIALIZATION = 64,
-    // One per space and common references.  Must be kSpaceMask aligned.
-    CODE_BACKREF_SERIALIZATION = 80,
-    // One per space, must be kSpaceMask aligned.
-    // Free: 89-95.
-    CODE_REFERENCE_SERIALIZATION = 96
-    // One per space, must be kSpaceMask aligned.
-    // Free: 105-255.
+  // Where the pointed-to object can be found:
+  enum Where {
+    kNewObject = 0,                 // Object is next in snapshot.
+    // 1-8                             One per space.
+    kRootArray = 0x9,               // Object is found in root array.
+    kPartialSnapshotCache = 0xa,    // Object is in the cache.
+    kExternalReference = 0xb,       // Pointer to an external reference.
+    // 0xc-0xf                         Free.
+    kBackref = 0x10,                 // Object is described relative to end.
+    // 0x11-0x18                       One per space.
+    // 0x19-0x1f                       Common backref offsets.
+    kFromStart = 0x20,              // Object is described relative to start.
+    // 0x21-0x28                       One per space.
+    // 0x29-0x2f                       Free.
+    // 0x30-0x3f                       Used by misc tags below.
+    kPointedToMask = 0x3f
   };
+
+  // How to code the pointer to the object.
+  enum HowToCode {
+    kPlain = 0,                          // Straight pointer.
+    // What this means depends on the architecture:
+    kFromCode = 0x40,                    // A pointer inlined in code.
+    kHowToCodeMask = 0x40
+  };
+
+  // Where to point within the object.
+  enum WhereToPoint {
+    kStartOfObject = 0,
+    kFirstInstruction = 0x80,
+    kWhereToPointMask = 0x80
+  };
+
+  // Misc.
+  // Raw data to be copied from the snapshot.
+  static const int kRawData = 0x30;
+  // Some common raw lengths: 0x31-0x3f
+  // A tag emitted at strategic points in the snapshot to delineate sections.
+  // If the deserializer does not find these at the expected moments then it
+  // is an indication that the snapshot and the VM do not fit together.
+  // Examine the build process for architecture, version or configuration
+  // mismatches.
+  static const int kSynchronize = 0x70;
+  // Used for the source code of the natives, which is in the executable, but
+  // is referred to from external strings in the snapshot.
+  static const int kNativesStringResource = 0x71;
+  static const int kNewPage = 0x72;
+  // 0x73-0x7f                            Free.
+  // 0xb0-0xbf                            Free.
+  // 0xf0-0xff                            Free.
+
+
   static const int kLargeData = LAST_SPACE;
   static const int kLargeCode = kLargeData + 1;
   static const int kLargeFixedArray = kLargeCode + 1;
   static const int kNumberOfSpaces = kLargeFixedArray + 1;
+  static const int kAnyOldSpace = -1;
 
   // A bitmask for getting the space out of an instruction.
   static const int kSpaceMask = 15;
@@ -396,10 +428,6 @@ class Serializer : public SerializerDeserializer {
 #endif
 
  protected:
-  enum ReferenceRepresentation {
-    TAGGED_REPRESENTATION,      // A tagged object reference.
-    CODE_TARGET_REPRESENTATION  // A reference to first instruction in target.
-  };
   static const int kInvalidRootIndex = -1;
   virtual int RootIndex(HeapObject* heap_object) = 0;
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) = 0;
@@ -409,11 +437,12 @@ class Serializer : public SerializerDeserializer {
     ObjectSerializer(Serializer* serializer,
                      Object* o,
                      SnapshotByteSink* sink,
-                     ReferenceRepresentation representation)
+                     HowToCode how_to_code,
+                     WhereToPoint where_to_point)
       : serializer_(serializer),
         object_(HeapObject::cast(o)),
         sink_(sink),
-        reference_representation_(representation),
+        reference_representation_(how_to_code + where_to_point),
         bytes_processed_so_far_(0) { }
     void Serialize();
     void VisitPointers(Object** start, Object** end);
@@ -435,16 +464,18 @@ class Serializer : public SerializerDeserializer {
     Serializer* serializer_;
     HeapObject* object_;
     SnapshotByteSink* sink_;
-    ReferenceRepresentation reference_representation_;
+    int reference_representation_;
     int bytes_processed_so_far_;
   };
 
   virtual void SerializeObject(Object* o,
-                               ReferenceRepresentation representation) = 0;
+                               HowToCode how_to_code,
+                               WhereToPoint where_to_point) = 0;
   void SerializeReferenceToPreviousObject(
       int space,
       int address,
-      ReferenceRepresentation reference_representation);
+      HowToCode how_to_code,
+      WhereToPoint where_to_point);
   void InitializeAllocators();
   // This will return the space for an object.  If the object is in large
   // object space it may return kLargeCode or kLargeFixedArray in order
@@ -492,7 +523,8 @@ class PartialSerializer : public Serializer {
   // Serialize the objects reachable from a single object pointer.
   virtual void Serialize(Object** o);
   virtual void SerializeObject(Object* o,
-                               ReferenceRepresentation representation);
+                               HowToCode how_to_code,
+                               WhereToPoint where_to_point);
 
  protected:
   virtual int RootIndex(HeapObject* o);
@@ -528,7 +560,8 @@ class StartupSerializer : public Serializer {
   // 3) Weak references (eg the symbol table).
   virtual void SerializeStrongReferences();
   virtual void SerializeObject(Object* o,
-                               ReferenceRepresentation representation);
+                               HowToCode how_to_code,
+                               WhereToPoint where_to_point);
   void SerializeWeakReferences();
   void Serialize() {
     SerializeStrongReferences();

src/x64/assembler-x64.cc

@@ -2800,6 +2800,16 @@ const int RelocInfo::kApplyMask = RelocInfo::kCodeTargetMask |
                                   1 << RelocInfo::INTERNAL_REFERENCE |
                                   1 << RelocInfo::JS_RETURN;
 
+
+bool RelocInfo::IsCodedSpecially() {
+  // The deserializer needs to know whether a pointer is specially coded.  Being
+  // specially coded on x64 means that it is a relative 32 bit address, as used
+  // by branch instructions.
+  return (1 << rmode_) & kApplyMask;
+}
+
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64