runtime/mem_map.h

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_RUNTIME_MEM_MAP_H_
#define ART_RUNTIME_MEM_MAP_H_

#include <string>

#include <stddef.h>
#include <sys/mman.h>  // For the PROT_* and MAP_* constants.
#include <sys/types.h>

#include "globals.h"

namespace art {

// Used to keep track of mmap segments.
//
// On 64b systems not supporting MAP_32BIT, the implementation of MemMap will do a linear scan
// for free pages. For security, the start of this scan should be randomized. This requires a
// dynamic initializer.
// For this to work, it is paramount that there are no other static initializers that access MemMap.
// Otherwise, calls might see uninitialized values.
class MemMap {
 public:
  // Request an anonymous region of length 'byte_count' and a requested base address.
  // Use NULL as the requested base address if you don't care.
  //
  // The word "anonymous" in this context means "not backed by a file". The supplied
  // 'ashmem_name' will be used -- on systems that support it -- to give the mapping
  // a name.
  //
  // On success, returns returns a MemMap instance.  On failure, returns a NULL;
  static MemMap* MapAnonymous(const char* ashmem_name, byte* addr, size_t byte_count, int prot,
                              bool low_4gb, std::string* error_msg);

  // Map part of a file, taking care of non-page aligned offsets.  The
  // "start" offset is absolute, not relative.
  //
  // On success, returns returns a MemMap instance.  On failure, returns a NULL;
  static MemMap* MapFile(size_t byte_count, int prot, int flags, int fd, off_t start,
                         const char* filename, std::string* error_msg) {
    return MapFileAtAddress(NULL, byte_count, prot, flags, fd, start, false, filename, error_msg);
  }

  // Map part of a file, taking care of non-page aligned offsets.  The
  // "start" offset is absolute, not relative. This version allows
  // requesting a specific address for the base of the mapping.
  //
  // On success, returns returns a MemMap instance.  On failure, returns a NULL;
  static MemMap* MapFileAtAddress(byte* addr, size_t byte_count, int prot, int flags, int fd,
                                  off_t start, bool reuse, const char* filename,
                                  std::string* error_msg);

  // Releases the memory mapping
  ~MemMap();

  const std::string& GetName() const {
    return name_;
  }

  bool Protect(int prot);

  int GetProtect() const {
    return prot_;
  }

  byte* Begin() const {
    return begin_;
  }

  size_t Size() const {
    return size_;
  }

  byte* End() const {
    return Begin() + Size();
  }

  void* BaseBegin() const {
    return base_begin_;
  }

  size_t BaseSize() const {
    return base_size_;
  }

  void* BaseEnd() const {
    return reinterpret_cast<byte*>(BaseBegin()) + BaseSize();
  }

  bool HasAddress(const void* addr) const {
    return Begin() <= addr && addr < End();
  }

  // Unmap the pages at end and remap them to create another memory map.
  MemMap* RemapAtEnd(byte* new_end, const char* tail_name, int tail_prot,
                     std::string* error_msg);

 private:
  MemMap(const std::string& name, byte* begin, size_t size, void* base_begin, size_t base_size,
         int prot);

  std::string name_;
  byte* const begin_;  // Start of data.
  size_t size_;  // Length of data.

  void* const base_begin_;  // Page-aligned base address.
  size_t base_size_;  // Length of mapping. May be changed by RemapAtEnd (ie Zygote).
  int prot_;  // Protection of the map.

#if defined(__LP64__) && !defined(__x86_64__)
  static uintptr_t next_mem_pos_;   // next memory location to check for low_4g extent
#endif

  friend class MemMapTest;  // To allow access to base_begin_ and base_size_.
};
std::ostream& operator<<(std::ostream& os, const MemMap& mem_map);

}  // namespace art

#endif  // ART_RUNTIME_MEM_MAP_H_