Deletion barrier preparation: validate overwritten references.

runtime/vm/virtual_memory_test.cc

 // 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.
 
 #include "platform/assert.h"
 #include "vm/unit_test.h"
 #include "vm/virtual_memory.h"
 
 namespace dart {
 
+bool IsZero(char* begin, char* end) {
+  for (char* current = begin; current < end; ++current) {
+    if (*current != 0) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
 UNIT_TEST_CASE(AllocateVirtualMemory) {
   const intptr_t kVirtualMemoryBlockSize = 64 * KB;
   VirtualMemory* vm = VirtualMemory::Reserve(kVirtualMemoryBlockSize);
   EXPECT(vm != NULL);
   EXPECT(vm->address() != NULL);
   EXPECT_EQ(kVirtualMemoryBlockSize, vm->size());
   EXPECT_EQ(vm->start(), reinterpret_cast<uword>(vm->address()));
   EXPECT_EQ(vm->start() + kVirtualMemoryBlockSize, vm->end());
   EXPECT(vm->Contains(vm->start()));
   EXPECT(vm->Contains(vm->start() + 1));
   EXPECT(vm->Contains(vm->start() + kVirtualMemoryBlockSize - 1));
   EXPECT(vm->Contains(vm->start() + (kVirtualMemoryBlockSize / 2)));
   EXPECT(!vm->Contains(vm->start() - 1));
   EXPECT(!vm->Contains(vm->end()));
   EXPECT(!vm->Contains(vm->end() + 1));
   EXPECT(!vm->Contains(0));
   EXPECT(!vm->Contains(static_cast<uword>(-1)));
 
   vm->Commit(false);
+
   char* buf = reinterpret_cast<char*>(vm->address());
+  EXPECT(IsZero(buf, buf + vm->size()));
   buf[0] = 'a';
   buf[1] = 'c';
   buf[2] = '/';
   buf[3] = 'd';
   buf[4] = 'c';
   buf[5] = 0;
   EXPECT_STREQ("ac/dc", buf);
 
   delete vm;
 }
@@ skipping 38 matching lines @@
 
 UNIT_TEST_CASE(VirtualMemoryCommitPartial) {
   const intptr_t kVirtualMemoryBlockSize = 3 * MB;
   VirtualMemory* vm = VirtualMemory::Reserve(kVirtualMemoryBlockSize);
   EXPECT(vm != NULL);
   // Commit only the middle MB and write to it.
   const uword commit_start = vm->start() + (1 * MB);
   const intptr_t kCommitSize = 1 * MB;
   vm->Commit(commit_start, kCommitSize, false);
   char* buf = reinterpret_cast<char*>(commit_start);
+  EXPECT(IsZero(buf, buf + kCommitSize));
   buf[0] = 'f';
   buf[1] = 'o';
   buf[2] = 'o';
   buf[3] = 0;
   EXPECT_STREQ("foo", buf);
   delete vm;
 }
 
 }  // namespace dart