linker_allocator.cpp revision bc23e530c4db5175a065eeef36553c9c2c78fcf4 
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#include "linker_allocator.h"
17#include <inttypes.h>
18#include <sys/mman.h>
19#include <unistd.h>
20
21struct LinkerAllocatorPage {
22  LinkerAllocatorPage* next;
23  uint8_t bytes[PAGE_SIZE-sizeof(LinkerAllocatorPage*)];
24};
25
26struct FreeBlockInfo {
27  void* next_block;
28  size_t num_free_blocks;
29};
30
31LinkerBlockAllocator::LinkerBlockAllocator()
32  : block_size_(0),
33    page_list_(nullptr),
34    free_block_list_(nullptr)
35{}
36
37void LinkerBlockAllocator::init(size_t block_size) {
38  block_size_ = block_size < sizeof(FreeBlockInfo) ? sizeof(FreeBlockInfo) : block_size;
39}
40
41
42void* LinkerBlockAllocator::alloc() {
43  if (free_block_list_ == nullptr) {
44    create_new_page();
45  }
46
47  FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(free_block_list_);
48  if (block_info->num_free_blocks > 1) {
49    FreeBlockInfo* next_block_info = reinterpret_cast<FreeBlockInfo*>(
50      reinterpret_cast<char*>(free_block_list_) + block_size_);
51    next_block_info->next_block = block_info->next_block;
52    next_block_info->num_free_blocks = block_info->num_free_blocks - 1;
53    free_block_list_ = next_block_info;
54  } else {
55    free_block_list_ = block_info->next_block;
56  }
57
58  block_info->next_block = nullptr;
59  block_info->num_free_blocks = 0;
60
61  return block_info;
62}
63
64void LinkerBlockAllocator::free(void* block) {
65  if (block == nullptr) {
66    return;
67  }
68
69  LinkerAllocatorPage* page = find_page(block);
70
71  if (page == nullptr) {
72    abort();
73  }
74
75  ssize_t offset = reinterpret_cast<uint8_t*>(block) - page->bytes;
76
77  if (offset % block_size_ != 0) {
78    abort();
79  }
80
81  FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(block);
82
83  block_info->next_block = free_block_list_;
84  block_info->num_free_blocks = 1;
85
86  free_block_list_ = block_info;
87}
88
89void LinkerBlockAllocator::protect_all(int prot) {
90  for (LinkerAllocatorPage* page = page_list_; page != nullptr; page = page->next) {
91    if (mprotect(page, PAGE_SIZE, prot) == -1) {
92      abort();
93    }
94  }
95}
96
97void LinkerBlockAllocator::create_new_page() {
98  LinkerAllocatorPage* page = reinterpret_cast<LinkerAllocatorPage*>(mmap(nullptr, PAGE_SIZE,
99      PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0));
100  if (page == MAP_FAILED) {
101    abort(); // oom
102  }
103
104  FreeBlockInfo* first_block = reinterpret_cast<FreeBlockInfo*>(page->bytes);
105  first_block->next_block = free_block_list_;
106  first_block->num_free_blocks = (PAGE_SIZE - sizeof(LinkerAllocatorPage*))/block_size_;
107
108  free_block_list_ = first_block;
109
110  page->next = page_list_;
111  page_list_ = page;
112}
113
114LinkerAllocatorPage* LinkerBlockAllocator::find_page(void* block) {
115  if (block == nullptr) {
116    abort();
117  }
118
119  LinkerAllocatorPage* page = page_list_;
120  const uint8_t* page_ptr = reinterpret_cast<const uint8_t*>(page);
121  while (page != nullptr) {
122    if (block >= (page_ptr + sizeof(page->next)) && block < (page_ptr + PAGE_SIZE)) {
123      return page;
124    }
125
126    page = page->next;
127  }
128
129  abort();
130}
131