text: /*
   * Copyright (C) 2013 Google Inc. 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 with the
   * distribution.
   *     * Neither the name of Google Inc. nor the names of its
   * contributors may be used to endorse or promote products derived from
   * this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #ifndef WTF_PageAllocator_h
  #define WTF_PageAllocator_h
  
  #include "wtf/Assertions.h"
  #include "wtf/CPU.h"
  #include "wtf/WTFExport.h"
  #include <stdint.h>
  
  namespace WTF {
  
  #if OS(WIN)
  static const size_t kPageAllocationGranularityShift = 16; // 64KB
  #else
  static const size_t kPageAllocationGranularityShift = 12; // 4KB
  #endif
  static const size_t kPageAllocationGranularity = 1 << kPageAllocationGranularityShift;
  static const size_t kPageAllocationGranularityOffsetMask = kPageAllocationGranularity - 1;
  static const size_t kPageAllocationGranularityBaseMask = ~kPageAllocationGranularityOffsetMask;
  
  // All Blink-supported systems have 4096 sized system pages and can handle
  // permissions and commit / decommit at this granularity.
  static const size_t kSystemPageSize = 4096;
  static const size_t kSystemPageOffsetMask = kSystemPageSize - 1;
  static const size_t kSystemPageBaseMask = ~kSystemPageOffsetMask;
  
  // Allocate one or more pages. Addresses in the range will be readable and
  // writeable but not executable.
  // The requested address is just a hint; the actual address returned may
  // differ. The returned address will be aligned at least to align bytes.
  // len is in bytes, and must be a multiple of kPageAllocationGranularity.
  // align is in bytes, and must be a power-of-two multiple of
  // kPageAllocationGranularity.
  // If addr is null, then a suitable and randomized address will be chosen
  // automatically.
  // This call will return null if the allocation cannot be satisfied.
  WTF_EXPORT void* allocPages(void* addr, size_t len, size_t align);
  
  // Free one or more pages.
  // addr and len must match a previous call to allocPages().
  WTF_EXPORT void freePages(void* addr, size_t len);
  
  // Mark one or more system pages as being inaccessible.
  // Subsequently accessing any address in the range will fault, and the
  // addresses will not be re-used by future allocations.
  // len must be a multiple of kSystemPageSize bytes.
  WTF_EXPORT void setSystemPagesInaccessible(void* addr, size_t len);
  
  // Mark one or more system pages as being accessible.
  // The pages will be readable and writeable.
  // len must be a multiple of kSystemPageSize bytes.
  WTF_EXPORT void setSystemPagesAccessible(void* addr, size_t len);
  
  // Decommit one or more system pages. Decommitted means that the physical memory
  // is released to the system, but the virtual address space remains reserved.
  // System pages are re-committed by calling recommitSystemPages(). Touching
  // a decommitted page _may_ fault.
  // Clients should not make any assumptions about the contents of decommitted
  // system pages, before or after they write to the page. The only guarantee
  // provided is that the contents of the system page will be deterministic again
  // after recommitting and writing to it. In particlar note that system pages are// not guaranteed to be zero-filled upon re-commit.
  // len must be a multiple of kSystemPageSize bytes.
  WTF_EXPORT void decommitSystemPages(void* addr, size_t len);
  
  // Recommit one or more system pages. Decommitted system pages must be
  // recommitted before they are read are written again.
  // Note that this operation may be a no-op on some platforms.
  // len must be a multiple of kSystemPageSize bytes.
  WTF_EXPORT void recommitSystemPages(void* addr, size_t len);
  
  } // namespace WTF
  
  #endif // WTF_PageAllocator_h
  