[heap] Fix MemoryChunk::kHeaderSize computation and add some assertions.

src/heap/spaces.h

 // Copyright 2011 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.
 
 #ifndef V8_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include "src/allocation.h"
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
@@ skipping 523 matching lines @@
   static void IncrementLiveBytesFromMutator(HeapObject* object, int by);
 
   static const intptr_t kAlignment =
       (static_cast<uintptr_t>(1) << kPageSizeBits);
 
   static const intptr_t kAlignmentMask = kAlignment - 1;
 
   static const intptr_t kSizeOffset = 0;
 
   static const intptr_t kLiveBytesOffset =
-      kSizeOffset + kPointerSize + kPointerSize + kPointerSize + kPointerSize +
-      kPointerSize + kPointerSize + kPointerSize + kPointerSize + kIntSize;
+      kSizeOffset + kPointerSize  // size_t size
+      + kIntptrSize               // intptr_t flags_
+      + kPointerSize              // Address area_start_
+      + kPointerSize              // Address area_end_
+      + 2 * kPointerSize          // base::VirtualMemory reservation_
+      + kPointerSize              // Address owner_
+      + kPointerSize              // Heap* heap_
+      + kIntSize;                 // int store_buffer_counter_
 
-  static const size_t kSlotsBufferOffset = kLiveBytesOffset + kIntSize;
+
+  static const size_t kSlotsBufferOffset =
+      kLiveBytesOffset + kIntSize;  // int live_byte_count_
 
   static const size_t kWriteBarrierCounterOffset =
-      kSlotsBufferOffset + kPointerSize + kPointerSize;
+      kSlotsBufferOffset + kPointerSize  // SlotsBuffer* slots_buffer_;
+      + kPointerSize;                    // SkipList* skip_list_;
 
-  static const size_t kHeaderSize = kWriteBarrierCounterOffset +
-                                    kPointerSize +  // write_barrier_counter_
-                                    kIntSize +      // progress_bar_
-                                    kIntSize +      // high_water_mark_
-                                    kPointerSize +  // mutex_ page lock
-                                    kPointerSize +  // parallel_sweeping_
-                                    5 * kPointerSize +  // free list statistics

[Michael Lippautz, 2015/09/07 16:55:25]

5 * kPointerSize implicitly included the memory that was needed to amount for
alignment requirements. (Maybe the author new this, maybe not.)

-                                    kPointerSize +      // next_chunk_
-                                    kPointerSize;       // prev_chunk_
+  static const size_t kMinHeaderSize =
+      kWriteBarrierCounterOffset +
+      kPointerSize     // intptr_t write_barrier_counter_
+      + kIntSize       // int progress_bar_
+      + kIntSize       // int high_water_mark_
+      + kPointerSize   // base::Mutex* mutex_
+      + kPointerSize   // base::AtomicWord parallel_sweeping_
+      + 5 * kIntSize   // int free-list statistics
+      + kPointerSize   // base::AtomicWord next_chunk_
+      + kPointerSize;  // base::AtomicWord prev_chunk_
+
+  // We add some more space to the computed header size to amount for missing
+  // alignment requirements in our computation.
+  static const size_t kHeaderSize = kMinHeaderSize + kPointerSize;
 
   static const int kBodyOffset =
       CODE_POINTER_ALIGN(kHeaderSize + Bitmap::kSize);
 
   // The start offset of the object area in a page. Aligned to both maps and
   // code alignment to be suitable for both.  Also aligned to 32 words because
   // the marking bitmap is arranged in 32 bit chunks.
   static const int kObjectStartAlignment = 32 * kPointerSize;
   static const int kObjectStartOffset =
       kBodyOffset - 1 +
@@ skipping 149 matching lines @@
                                  Address area_start, Address area_end,
                                  Executability executable, Space* owner);
 
  private:
   // next_chunk_ holds a pointer of type MemoryChunk
   base::AtomicWord next_chunk_;
   // prev_chunk_ holds a pointer of type MemoryChunk
   base::AtomicWord prev_chunk_;
 
   friend class MemoryAllocator;
+  friend class MemoryChunkValidator;
 };
 
 
-STATIC_ASSERT(sizeof(MemoryChunk) <= MemoryChunk::kHeaderSize);
-
-
 // -----------------------------------------------------------------------------
 // A page is a memory chunk of a size 1MB. Large object pages may be larger.
 //
 // The only way to get a page pointer is by calling factory methods:
 //   Page* p = Page::FromAddress(addr); or
 //   Page* p = Page::FromAllocationTop(top);
 class Page : public MemoryChunk {
  public:
   // Returns the page containing a given address. The address ranges
   // from [page_addr .. page_addr + kPageSize[
@@ skipping 88 matching lines @@
 #undef FRAGMENTATION_STATS_ACCESSORS
 
 #ifdef DEBUG
   void Print();
 #endif  // DEBUG
 
   friend class MemoryAllocator;
 };
 
 
-STATIC_ASSERT(sizeof(Page) <= MemoryChunk::kHeaderSize);
-
-
 class LargePage : public MemoryChunk {
  public:
   HeapObject* GetObject() { return HeapObject::FromAddress(area_start()); }
 
   inline LargePage* next_page() const {
     return static_cast<LargePage*>(next_chunk());
   }
 
   inline void set_next_page(LargePage* page) { set_next_chunk(page); }
 
  private:
   static inline LargePage* Initialize(Heap* heap, MemoryChunk* chunk);
 
   friend class MemoryAllocator;
 };
 
-STATIC_ASSERT(sizeof(LargePage) <= MemoryChunk::kHeaderSize);
 
 // ----------------------------------------------------------------------------
 // Space is the abstract superclass for all allocation spaces.
 class Space : public Malloced {
  public:
   Space(Heap* heap, AllocationSpace id, Executability executable)
       : heap_(heap), id_(id), executable_(executable) {}
 
   virtual ~Space() {}
 
@@ skipping 33 matching lines @@
   virtual void Print() = 0;
 #endif
 
  private:
   Heap* heap_;
   AllocationSpace id_;
   Executability executable_;
 };
 
 
+class MemoryChunkValidator {
+  // Computed offsets should match the compiler generates ones.
+  STATIC_ASSERT(MemoryChunk::kSizeOffset == offsetof(MemoryChunk, size_));
+  STATIC_ASSERT(MemoryChunk::kLiveBytesOffset ==
+                offsetof(MemoryChunk, live_byte_count_));
+  STATIC_ASSERT(MemoryChunk::kSlotsBufferOffset ==
+                offsetof(MemoryChunk, slots_buffer_));
+  STATIC_ASSERT(MemoryChunk::kWriteBarrierCounterOffset ==
+                offsetof(MemoryChunk, write_barrier_counter_));
+
+  // Validate our estimates on the header size.
+  STATIC_ASSERT(sizeof(MemoryChunk) <= MemoryChunk::kHeaderSize);
+  STATIC_ASSERT(sizeof(LargePage) <= MemoryChunk::kHeaderSize);
+  STATIC_ASSERT(sizeof(Page) <= MemoryChunk::kHeaderSize);
+};
+
+
 // ----------------------------------------------------------------------------
 // All heap objects containing executable code (code objects) must be allocated
 // from a 2 GB range of memory, so that they can call each other using 32-bit
 // displacements.  This happens automatically on 32-bit platforms, where 32-bit
 // displacements cover the entire 4GB virtual address space.  On 64-bit
 // platforms, we support this using the CodeRange object, which reserves and
 // manages a range of virtual memory.
 class CodeRange {
  public:
   explicit CodeRange(Isolate* isolate);
@@ skipping 1968 matching lines @@
     count = 0;
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_SPACES_H_