Make randomized allocations along 64k granularity boundaries to avoid comitti...

src/platform-win32.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 827 matching lines @@
   }
   return allocate_alignment;
 }
 
 
 void* OS::Allocate(const size_t requested,
                    size_t* allocated,
                    bool is_executable) {
   // The address range used to randomize RWX allocations in OS::Allocate
   // Try not to map pages into the default range that windows loads DLLs
+  // Use a multiple of 64k to prevent committing unused memory.
   // Note: This does not guarantee RWX regions will be within the
   // range kAllocationRandomAddressMin to kAllocationRandomAddressMax
 #ifdef V8_HOST_ARCH_64_BIT
   static const intptr_t kAllocationRandomAddressMin = 0x0000000080000000;
-  static const intptr_t kAllocationRandomAddressMax = 0x000004FFFFFFFFFF;
+  static const intptr_t kAllocationRandomAddressMax = 0x000003FFFFFF0000;
 #else
   static const intptr_t kAllocationRandomAddressMin = 0x04000000;
-  static const intptr_t kAllocationRandomAddressMax = 0x4FFFFFFF;
+  static const intptr_t kAllocationRandomAddressMax = 0x3FFF0000;
 #endif
 
   // VirtualAlloc rounds allocated size to page size automatically.
   size_t msize = RoundUp(requested, static_cast<int>(GetPageSize()));
   intptr_t address = NULL;
 
   // Windows XP SP2 allows Data Excution Prevention (DEP).
   int prot = is_executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
 
   // For exectutable pages try and randomize the allocation address
@@ skipping 1081 matching lines @@
 
   // Release the thread handles
   CloseHandle(data_->sampler_thread_);
   CloseHandle(data_->profiled_thread_);
 }
 
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal