Fixed zapping of contents

BUG=

Review-Url: https://codereview.chromium.org/2377943003
Cr-Commit-Position: refs/heads/master@{#39946}

BUILD.gn

@@ -1706,6 +1706,7 @@ v8_source_set("v8_base") {
     "src/zone/zone-allocator.h",
     "src/zone/zone-allocator.h",
     "src/zone/zone-containers.h",
+    "src/zone/zone-segment.cc",
     "src/zone/zone-segment.h",
     "src/zone/zone.cc",
     "src/zone/zone.h",

src/v8.gyp

@@ -1273,6 +1273,7 @@
         'wasm/wasm-result.h',
         'zone/accounting-allocator.cc',
         'zone/accounting-allocator.h',
+        'zone/zone-segment.cc',
         'zone/zone-segment.h',
         'zone/zone.cc',
         'zone/zone.h',

src/zone/accounting-allocator.cc

@@ -29,6 +29,7 @@ Segment* AccountingAllocator::AllocateSegment(size_t bytes) {
 void AccountingAllocator::FreeSegment(Segment* memory) {
   base::NoBarrier_AtomicIncrement(
       &current_memory_usage_, -static_cast<base::AtomicWord>(memory->size()));
+  memory->ZapHeader();
   free(memory);
 }
 

src/zone/zone-segment.cc

+// Copyright 2016 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/zone/zone-segment.h"
+
+namespace v8 {
+namespace internal {
+
+void Segment::ZapContents() {
+#ifdef DEBUG
+  memset(start(), kZapDeadByte, capacity());
+#endif
+}
+
+void Segment::ZapHeader() {
+#ifdef DEBUG
+  memset(this, kZapDeadByte, sizeof(Segment));
+#endif
+}
+}  // namespace internal
+}  // namespace v8

src/zone/zone-segment.h

@@ -38,7 +38,16 @@ class Segment {
   Address start() const { return address(sizeof(Segment)); }
   Address end() const { return address(size_); }
 
+  // Zap the contents of the segment (but not the header).
+  void ZapContents();
+  // Zaps the header and makes the segment unusable this way.
+  void ZapHeader();
+
  private:
+#ifdef DEBUG
+  // Constant byte value used for zapping dead memory in debug mode.
+  static const unsigned char kZapDeadByte = 0xcd;
+#endif
   // Computes the address of the nth byte in this segment.
   Address address(size_t n) const { return Address(this) + n; }
 

src/zone/zone.cc

@@ -92,11 +92,6 @@ void* Zone::New(size_t size) {
 }
 
 void Zone::DeleteAll() {
-#ifdef DEBUG
-  // Constant byte value used for zapping dead memory in debug mode.
-  static const unsigned char kZapDeadByte = 0xcd;
-#endif
-
   // Find a segment with a suitable size to keep around.
   Segment* keep = nullptr;
   // Traverse the chained list of segments, zapping (in debug mode)
@@ -112,9 +107,8 @@ void Zone::DeleteAll() {
 #ifdef DEBUG
       // Un-poison first so the zapping doesn't trigger ASan complaints.
       ASAN_UNPOISON_MEMORY_REGION(current, size);
-      // Zap the entire current segment (including the header).
-      memset(current, kZapDeadByte, size);
 #endif
+      current->ZapContents();
       segment_bytes_allocated_ -= size;
       allocator_->FreeSegment(current);
     }
@@ -131,10 +125,7 @@ void Zone::DeleteAll() {
     limit_ = keep->end();
     // Un-poison so we can re-use the segment later.
     ASAN_UNPOISON_MEMORY_REGION(start, keep->capacity());
-#ifdef DEBUG
-    // Zap the contents of the kept segment (but not the header).
-    memset(start, kZapDeadByte, keep->capacity());
-#endif
+    keep->ZapContents();
   } else {
     position_ = limit_ = 0;
   }
@@ -145,20 +136,14 @@ void Zone::DeleteAll() {
 }
 
 void Zone::DeleteKeptSegment() {
-#ifdef DEBUG
-  // Constant byte value used for zapping dead memory in debug mode.
-  static const unsigned char kZapDeadByte = 0xcd;
-#endif
-
   DCHECK(segment_head_ == nullptr || segment_head_->next() == nullptr);
   if (segment_head_ != nullptr) {
     size_t size = segment_head_->size();
 #ifdef DEBUG
     // Un-poison first so the zapping doesn't trigger ASan complaints.
     ASAN_UNPOISON_MEMORY_REGION(segment_head_, size);
-    // Zap the entire kept segment (including the header).
-    memset(segment_head_, kZapDeadByte, size);
 #endif
+    segment_head_->ZapContents();
     segment_bytes_allocated_ -= size;
     allocator_->FreeSegment(segment_head_);
     segment_head_ = nullptr;