linker/linker_block_allocator.h

/*
 * Copyright (C) 2014 The Android Open Source Project
 * 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.
 *
 * 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.
 */

#pragma once

#include <stdlib.h>
#include <limits.h>

#include <android-base/macros.h>

static constexpr size_t kBlockSizeAlign = sizeof(void*);
static constexpr size_t kBlockSizeMin = sizeof(void*) * 2;

struct LinkerBlockAllocatorPage;

/*
 * This class is a non-template version of the LinkerTypeAllocator
 * It keeps code inside .cpp file by keeping the interface
 * template-free.
 *
 * Please use LinkerTypeAllocator<type> where possible (everywhere).
 */
class LinkerBlockAllocator {
 public:
  explicit LinkerBlockAllocator(size_t block_size);

  void* alloc();
  void free(void* block);
  void protect_all(int prot);

  // Purge all pages if all previously allocated blocks have been freed.
  void purge();

 private:
  void create_new_page();
  LinkerBlockAllocatorPage* find_page(void* block);

  size_t block_size_;
  LinkerBlockAllocatorPage* page_list_;
  void* free_block_list_;
  size_t allocated_;

  DISALLOW_COPY_AND_ASSIGN(LinkerBlockAllocator);
};

/*
 * A simple allocator for the dynamic linker. An allocator allocates instances
 * of a single fixed-size type. Allocations are backed by page-sized private
 * anonymous mmaps.
 *
 * The differences between this allocator and BionicAllocator are:
 * 1. This allocator manages space more efficiently. BionicAllocator operates in
 *    power-of-two sized blocks up to 1k, when this implementation splits the
 *    page to aligned size of structure; For example for structures with size
 *    513 this allocator will use 516 (520 for lp64) bytes of data where
 *    generalized implementation is going to use 1024 sized blocks.
 *
 * 2. This allocator does not munmap allocated memory, where BionicAllocator does.
 *
 * 3. This allocator provides mprotect services to the user, where BionicAllocator
 *    always treats its memory as READ|WRITE.
 */
template<typename T>
class LinkerTypeAllocator {
 public:
  LinkerTypeAllocator() : block_allocator_(sizeof(T)) {}
  T* alloc() { return reinterpret_cast<T*>(block_allocator_.alloc()); }
  void free(T* t) { block_allocator_.free(t); }
  void protect_all(int prot) { block_allocator_.protect_all(prot); }
 private:
  LinkerBlockAllocator block_allocator_;
  DISALLOW_COPY_AND_ASSIGN(LinkerTypeAllocator);
};