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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef __LINKER_BLOCK_ALLOCATOR_H
     18 #define __LINKER_BLOCK_ALLOCATOR_H
     19 
     20 #include <stdlib.h>
     21 #include <limits.h>
     22 #include "private/bionic_macros.h"
     23 
     24 struct LinkerBlockAllocatorPage;
     25 
     26 /*
     27  * This class is a non-template version of the LinkerTypeAllocator
     28  * It keeps code inside .cpp file by keeping the interface
     29  * template-free.
     30  *
     31  * Please use LinkerTypeAllocator<type> where possible (everywhere).
     32  */
     33 class LinkerBlockAllocator {
     34  public:
     35   explicit LinkerBlockAllocator(size_t block_size);
     36 
     37   void* alloc();
     38   void free(void* block);
     39   void protect_all(int prot);
     40 
     41  private:
     42   void create_new_page();
     43   LinkerBlockAllocatorPage* find_page(void* block);
     44 
     45   size_t block_size_;
     46   LinkerBlockAllocatorPage* page_list_;
     47   void* free_block_list_;
     48 
     49   DISALLOW_COPY_AND_ASSIGN(LinkerBlockAllocator);
     50 };
     51 
     52 /*
     53  * A simple allocator for the dynamic linker. An allocator allocates instances
     54  * of a single fixed-size type. Allocations are backed by page-sized private
     55  * anonymous mmaps.
     56  *
     57  * The differences between this allocator and LinkerMemoryAllocator are:
     58  * 1. This allocator manages space more efficiently. LinkerMemoryAllocator
     59  *    operates in power-of-two sized blocks up to 1k, when this implementation
     60  *    splits the page to aligned size of structure; For example for structures
     61  *    with size 513 this allocator will use 516 (520 for lp64) bytes of data
     62  *    where generalized implementation is going to use 1024 sized blocks.
     63  *
     64  * 2. This allocator does not munmap allocated memory, where LinkerMemoryAllocator does.
     65  *
     66  * 3. This allocator provides mprotect services to the user, where LinkerMemoryAllocator
     67  *    always treats it's memory as READ|WRITE.
     68  */
     69 template<typename T>
     70 class LinkerTypeAllocator {
     71  public:
     72   LinkerTypeAllocator() : block_allocator_(sizeof(T)) {}
     73   T* alloc() { return reinterpret_cast<T*>(block_allocator_.alloc()); }
     74   void free(T* t) { block_allocator_.free(t); }
     75   void protect_all(int prot) { block_allocator_.protect_all(prot); }
     76  private:
     77   LinkerBlockAllocator block_allocator_;
     78   DISALLOW_COPY_AND_ASSIGN(LinkerTypeAllocator);
     79 };
     80 
     81 #endif // __LINKER_BLOCK_ALLOCATOR_H
     82