Serializer: support all alignment kinds.

src/snapshot/serialize.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/platform/platform.h"
 #include "src/bootstrapper.h"
@@ skipping 735 matching lines @@
     }
     isolate_->heap()->set_allocation_sites_list(site);
   } else if (obj->IsCode()) {
     // We flush all code pages after deserializing the startup snapshot. In that
     // case, we only need to remember code objects in the large object space.
     // When deserializing user code, remember each individual code object.
     if (deserializing_user_code() || space == LO_SPACE) {
       new_code_objects_.Add(Code::cast(obj));
     }
   }
+  // Check alignment.
+  DCHECK_EQ(0, Heap::GetFillToAlign(obj->address(), obj->RequiredAlignment()));
   return obj;
 }
 
 
 HeapObject* Deserializer::GetBackReferencedObject(int space) {
   HeapObject* obj;
   BackReference back_reference(source_.GetInt());
   if (space == LO_SPACE) {
     CHECK(back_reference.chunk_index() == 0);
     uint32_t index = back_reference.large_object_index();
     obj = deserialized_large_objects_[index];
   } else {
     DCHECK(space < kNumberOfPreallocatedSpaces);
     uint32_t chunk_index = back_reference.chunk_index();
     DCHECK_LE(chunk_index, current_chunk_[space]);
     uint32_t chunk_offset = back_reference.chunk_offset();
-    obj = HeapObject::FromAddress(reservations_[space][chunk_index].start +
-                                  chunk_offset);
+    Address address = reservations_[space][chunk_index].start + chunk_offset;
+    if (next_alignment_ != kWordAligned) {
+      int padding = Heap::GetFillToAlign(address, next_alignment_);
+      next_alignment_ = kWordAligned;
+      DCHECK(padding == 0 || HeapObject::FromAddress(address)->IsFiller());
+      address += padding;
+    }
+    obj = HeapObject::FromAddress(address);
   }
   if (deserializing_user_code() && obj->IsInternalizedString()) {
     obj = String::cast(obj)->GetForwardedInternalizedString();
   }
   hot_objects_.Add(obj);
   return obj;
 }
 
 
 // This routine writes the new object into the pointer provided and then
 // returns true if the new object was in young space and false otherwise.
 // The reason for this strange interface is that otherwise the object is
 // written very late, which means the FreeSpace map is not set up by the
 // time we need to use it to mark the space at the end of a page free.
 void Deserializer::ReadObject(int space_number, Object** write_back) {
   Address address;
   HeapObject* obj;
-  int next_int = source_.GetInt();
+  int size = source_.GetInt() << kObjectAlignmentBits;
 
-  bool double_align = false;
-#ifndef V8_HOST_ARCH_64_BIT
-  double_align = next_int == kDoubleAlignmentSentinel;
-  if (double_align) next_int = source_.GetInt();
-#endif
-
-  DCHECK_NE(kDoubleAlignmentSentinel, next_int);
-  int size = next_int << kObjectAlignmentBits;
-  int reserved_size = size + (double_align ? kPointerSize : 0);
-  address = Allocate(space_number, reserved_size);
-  obj = HeapObject::FromAddress(address);
-  if (double_align) {
-    obj = isolate_->heap()->DoubleAlignForDeserialization(obj, reserved_size);
+  if (next_alignment_ != kWordAligned) {
+    int reserved = size + Heap::GetMaximumFillToAlign(next_alignment_);
+    address = Allocate(space_number, reserved);
+    obj = HeapObject::FromAddress(address);
+    // If one of the following assertions fails, then we are deserializing an
+    // aligned object when the filler maps have not been deserialized yet.
+    // We require filler maps as padding to align the object.
+    Heap* heap = isolate_->heap();
+    DCHECK(heap->free_space_map()->IsMap());
+    DCHECK(heap->one_pointer_filler_map()->IsMap());
+    DCHECK(heap->two_pointer_filler_map()->IsMap());
+    obj = heap->AlignWithFiller(obj, size, reserved, next_alignment_);
     address = obj->address();
+    next_alignment_ = kWordAligned;
+  } else {
+    address = Allocate(space_number, size);
+    obj = HeapObject::FromAddress(address);
   }
 
   isolate_->heap()->OnAllocationEvent(obj, size);
   Object** current = reinterpret_cast<Object**>(address);
   Object** limit = current + (size >> kPointerSizeLog2);
   if (FLAG_log_snapshot_positions) {
     LOG(isolate_, SnapshotPositionEvent(address, source_.position()));
   }
 
   if (ReadData(current, limit, space_number, address)) {
@@ skipping 174 matching lines @@
   case byte_code + 1:                     \
   case byte_code + 2:                     \
   case byte_code + 3:
 
 #define SIXTEEN_CASES(byte_code)          \
   FOUR_CASES(byte_code)                   \
   FOUR_CASES(byte_code + 4)               \
   FOUR_CASES(byte_code + 8)               \
   FOUR_CASES(byte_code + 12)
 
+#define SINGLE_CASE(where, how, within, space) \
+  CASE_STATEMENT(where, how, within, space)    \
+  CASE_BODY(where, how, within, space)
+
       // Deserialize a new object and write a pointer to it to the current
       // object.
       ALL_SPACES(kNewObject, kPlain, kStartOfObject)
       // Support for direct instruction pointers in functions.  It's an inner
       // pointer because it points at the entry point, not at the start of the
       // code object.
-      CASE_STATEMENT(kNewObject, kPlain, kInnerPointer, CODE_SPACE)
-      CASE_BODY(kNewObject, kPlain, kInnerPointer, CODE_SPACE)
+      SINGLE_CASE(kNewObject, kPlain, kInnerPointer, CODE_SPACE)
       // Deserialize a new code object and write a pointer to its first
       // instruction to the current code object.
       ALL_SPACES(kNewObject, kFromCode, kInnerPointer)
       // Find a recently deserialized object using its offset from the current
       // allocation point and write a pointer to it to the current object.
       ALL_SPACES(kBackref, kPlain, kStartOfObject)
       ALL_SPACES(kBackrefWithSkip, kPlain, kStartOfObject)
 #if defined(V8_TARGET_ARCH_MIPS) || defined(V8_TARGET_ARCH_MIPS64) || \
     defined(V8_TARGET_ARCH_PPC) || V8_EMBEDDED_CONSTANT_POOL
       // Deserialize a new object from pointer found in code and write
@@ skipping 10 matching lines @@
       // Find a recently deserialized code object using its offset from the
       // current allocation point and write a pointer to its first instruction
       // to the current code object or the instruction pointer in a function
       // object.
       ALL_SPACES(kBackref, kFromCode, kInnerPointer)
       ALL_SPACES(kBackrefWithSkip, kFromCode, kInnerPointer)
       ALL_SPACES(kBackref, kPlain, kInnerPointer)
       ALL_SPACES(kBackrefWithSkip, kPlain, kInnerPointer)
       // Find an object in the roots array and write a pointer to it to the
       // current object.
-      CASE_STATEMENT(kRootArray, kPlain, kStartOfObject, 0)
-      CASE_BODY(kRootArray, kPlain, kStartOfObject, 0)
+      SINGLE_CASE(kRootArray, kPlain, kStartOfObject, 0)
 #if defined(V8_TARGET_ARCH_MIPS) || defined(V8_TARGET_ARCH_MIPS64) || \
     defined(V8_TARGET_ARCH_PPC) || V8_EMBEDDED_CONSTANT_POOL
       // Find an object in the roots array and write a pointer to it to in code.
-      CASE_STATEMENT(kRootArray, kFromCode, kStartOfObject, 0)
-      CASE_BODY(kRootArray, kFromCode, kStartOfObject, 0)
+      SINGLE_CASE(kRootArray, kFromCode, kStartOfObject, 0)
 #endif
       // Find an object in the partial snapshots cache and write a pointer to it
       // to the current object.
-      CASE_STATEMENT(kPartialSnapshotCache, kPlain, kStartOfObject, 0)
-      CASE_BODY(kPartialSnapshotCache, kPlain, kStartOfObject, 0)
+      SINGLE_CASE(kPartialSnapshotCache, kPlain, kStartOfObject, 0)
       // Find an code entry in the partial snapshots cache and
       // write a pointer to it to the current object.
-      CASE_STATEMENT(kPartialSnapshotCache, kPlain, kInnerPointer, 0)
-      CASE_BODY(kPartialSnapshotCache, kPlain, kInnerPointer, 0)
+      SINGLE_CASE(kPartialSnapshotCache, kPlain, kInnerPointer, 0)
       // Find an external reference and write a pointer to it to the current
       // object.
-      CASE_STATEMENT(kExternalReference, kPlain, kStartOfObject, 0)
-      CASE_BODY(kExternalReference, kPlain, kStartOfObject, 0)
+      SINGLE_CASE(kExternalReference, kPlain, kStartOfObject, 0)
       // Find an external reference and write a pointer to it in the current
       // code object.
-      CASE_STATEMENT(kExternalReference, kFromCode, kStartOfObject, 0)
-      CASE_BODY(kExternalReference, kFromCode, kStartOfObject, 0)
+      SINGLE_CASE(kExternalReference, kFromCode, kStartOfObject, 0)
       // Find an object in the attached references and write a pointer to it to
       // the current object.
-      CASE_STATEMENT(kAttachedReference, kPlain, kStartOfObject, 0)
-      CASE_BODY(kAttachedReference, kPlain, kStartOfObject, 0)
-      CASE_STATEMENT(kAttachedReference, kPlain, kInnerPointer, 0)
-      CASE_BODY(kAttachedReference, kPlain, kInnerPointer, 0)
-      CASE_STATEMENT(kAttachedReference, kFromCode, kInnerPointer, 0)
-      CASE_BODY(kAttachedReference, kFromCode, kInnerPointer, 0)
+      SINGLE_CASE(kAttachedReference, kPlain, kStartOfObject, 0)
+      SINGLE_CASE(kAttachedReference, kPlain, kInnerPointer, 0)
+      SINGLE_CASE(kAttachedReference, kFromCode, kInnerPointer, 0)
       // Find a builtin and write a pointer to it to the current object.
-      CASE_STATEMENT(kBuiltin, kPlain, kStartOfObject, 0)
-      CASE_BODY(kBuiltin, kPlain, kStartOfObject, 0)
-      CASE_STATEMENT(kBuiltin, kPlain, kInnerPointer, 0)
-      CASE_BODY(kBuiltin, kPlain, kInnerPointer, 0)
-      CASE_STATEMENT(kBuiltin, kFromCode, kInnerPointer, 0)
-      CASE_BODY(kBuiltin, kFromCode, kInnerPointer, 0)
+      SINGLE_CASE(kBuiltin, kPlain, kStartOfObject, 0)
+      SINGLE_CASE(kBuiltin, kPlain, kInnerPointer, 0)
+      SINGLE_CASE(kBuiltin, kFromCode, kInnerPointer, 0)
 
 #undef CASE_STATEMENT
 #undef CASE_BODY
 #undef ALL_SPACES
 
       case kSkip: {
         int size = source_.GetInt();
         current = reinterpret_cast<Object**>(
             reinterpret_cast<intptr_t>(current) + size);
         break;
@@ skipping 74 matching lines @@
       }
 
       case kVariableRepeat: {
         int repeats = source_.GetInt();
         Object* object = current[-1];
         DCHECK(!isolate->heap()->InNewSpace(object));
         for (int i = 0; i < repeats; i++) UnalignedCopy(current++, &object);
         break;
       }
 
+      case kAlignmentPrefix:
+      case kAlignmentPrefix + 1:
+      case kAlignmentPrefix + 2: {
+        DCHECK_EQ(kWordAligned, next_alignment_);
+        next_alignment_ =
+            static_cast<AllocationAlignment>(data - (kAlignmentPrefix - 1));
+        break;
+      }
+
       STATIC_ASSERT(kNumberOfRootArrayConstants == Heap::kOldSpaceRoots);
       STATIC_ASSERT(kNumberOfRootArrayConstants == 32);
       SIXTEEN_CASES(kRootArrayConstantsWithSkip)
       SIXTEEN_CASES(kRootArrayConstantsWithSkip + 16) {
         int skip = source_.GetInt();
         current = reinterpret_cast<Object**>(
             reinterpret_cast<intptr_t>(current) + skip);
         // Fall through.
       }
 
@@ skipping 46 matching lines @@
         int repeats = data - kFixedRepeatStart;
         Object* object;
         UnalignedCopy(&object, current - 1);
         DCHECK(!isolate->heap()->InNewSpace(object));
         for (int i = 0; i < repeats; i++) UnalignedCopy(current++, &object);
         break;
       }
 
 #undef SIXTEEN_CASES
 #undef FOUR_CASES
+#undef SINGLE_CASE
 
       default:
         CHECK(false);
     }
   }
   CHECK_EQ(limit, current);
   return true;
 }
 
 
@@ skipping 307 matching lines @@
       DCHECK(how_to_code == kPlain && where_to_point == kStartOfObject);
       sink_->Put(kAttachedReference + kPlain + kStartOfObject, "Global Proxy");
       sink_->PutInt(kGlobalProxyReference, "kGlobalProxyReference");
     } else {
       if (FLAG_trace_serializer) {
         PrintF(" Encoding back reference to: ");
         obj->ShortPrint();
         PrintF("\n");
       }
 
+      PutAlignmentPrefix(obj);
       AllocationSpace space = back_reference.space();
       if (skip == 0) {
         sink_->Put(kBackref + how_to_code + where_to_point + space, "BackRef");
       } else {
         sink_->Put(kBackrefWithSkip + how_to_code + where_to_point + space,
                    "BackRefWithSkip");
         sink_->PutInt(skip, "BackRefSkipDistance");
       }
       PutBackReference(obj, back_reference);
     }
@@ skipping 73 matching lines @@
 }
 
 
 void Serializer::PutBackReference(HeapObject* object, BackReference reference) {
   DCHECK(BackReferenceIsAlreadyAllocated(reference));
   sink_->PutInt(reference.reference(), "BackRefValue");
   hot_objects_.Add(object);
 }
 
 
+int Serializer::PutAlignmentPrefix(HeapObject* object) {
+  AllocationAlignment alignment = object->RequiredAlignment();
+  if (alignment != kWordAligned) {
+    DCHECK(1 <= alignment && alignment <= 3);
+    byte prefix = (kAlignmentPrefix - 1) + alignment;
+    sink_->Put(prefix, "Alignment");
+    return Heap::GetMaximumFillToAlign(alignment);
+  }
+  return 0;
+}
+
+
 void PartialSerializer::SerializeObject(HeapObject* obj, HowToCode how_to_code,
                                         WhereToPoint where_to_point, int skip) {
   if (obj->IsMap()) {
     // The code-caches link to context-specific code objects, which
     // the startup and context serializes cannot currently handle.
     DCHECK(Map::cast(obj)->code_cache() == obj->GetHeap()->empty_fixed_array());
   }
 
   // Replace typed arrays by undefined.
   if (obj->IsJSTypedArray()) obj = isolate_->heap()->undefined_value();
@@ skipping 61 matching lines @@
     sink_->Put(kNewObject + reference_representation_ + space,
                "NewLargeObject");
     sink_->PutInt(size >> kObjectAlignmentBits, "ObjectSizeInWords");
     if (object_->IsCode()) {
       sink_->Put(EXECUTABLE, "executable large object");
     } else {
       sink_->Put(NOT_EXECUTABLE, "not executable large object");
     }
     back_reference = serializer_->AllocateLargeObject(size);
   } else {
-    bool needs_double_align = false;
-    // TODO(bbudge): Generalize to other alignment constraints.
-    if (object_->RequiredAlignment() == kDoubleAligned) {
-      // Add wriggle room for double alignment padding.
-      back_reference = serializer_->Allocate(space, size + kPointerSize);
-      needs_double_align = true;
-    } else {
-      back_reference = serializer_->Allocate(space, size);
-    }
+    int fill = serializer_->PutAlignmentPrefix(object_);
+    back_reference = serializer_->Allocate(space, size + fill);
     sink_->Put(kNewObject + reference_representation_ + space, "NewObject");
-    if (needs_double_align)
-      sink_->PutInt(kDoubleAlignmentSentinel, "DoubleAlignSentinel");
-    int encoded_size = size >> kObjectAlignmentBits;
-    DCHECK_NE(kDoubleAlignmentSentinel, encoded_size);
-    sink_->PutInt(encoded_size, "ObjectSizeInWords");
+    sink_->PutInt(size >> kObjectAlignmentBits, "ObjectSizeInWords");
   }
 
 #ifdef OBJECT_PRINT
   if (FLAG_serialization_statistics) {
     serializer_->CountInstanceType(map, size);
   }
 #endif  // OBJECT_PRINT
 
   // Mark this object as already serialized.
   serializer_->back_reference_map()->Add(object_, back_reference);
@@ skipping 934 matching lines @@
   SerializedCodeData* scd = new SerializedCodeData(cached_data);
   SanityCheckResult r = scd->SanityCheck(isolate, source);
   if (r == CHECK_SUCCESS) return scd;
   cached_data->Reject();
   source->GetIsolate()->counters()->code_cache_reject_reason()->AddSample(r);
   delete scd;
   return NULL;
 }
 }  // namespace internal
 }  // namespace v8