linker_allocator.cpp revision d59e50063ad708509f3ad83350be33f5612c4f54 
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  memset(block_info, 0, block_size_);
59
60  return block_info;
61}
62
63void LinkerBlockAllocator::free(void* block) {
64  if (block == nullptr) {
65    return;
66  }
67
68  LinkerAllocatorPage* page = find_page(block);
69
70  if (page == nullptr) {
71    abort();
72  }
73
74  ssize_t offset = reinterpret_cast<uint8_t*>(block) - page->bytes;
75
76  if (offset % block_size_ != 0) {
77    abort();
78  }
79
80  memset(block, 0, block_size_);
81
82  FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(block);
83
84  block_info->next_block = free_block_list_;
85  block_info->num_free_blocks = 1;
86
87  free_block_list_ = block_info;
88}
89
90void LinkerBlockAllocator::protect_all(int prot) {
91  for (LinkerAllocatorPage* page = page_list_; page != nullptr; page = page->next) {
92    if (mprotect(page, PAGE_SIZE, prot) == -1) {
93      abort();
94    }
95  }
96}
97
98void LinkerBlockAllocator::create_new_page() {
99  LinkerAllocatorPage* page = reinterpret_cast<LinkerAllocatorPage*>(mmap(nullptr, PAGE_SIZE,
100      PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0));
101  if (page == MAP_FAILED) {
102    abort(); // oom
103  }
104  memset(page, 0, PAGE_SIZE);
105
106  FreeBlockInfo* first_block = reinterpret_cast<FreeBlockInfo*>(page->bytes);
107  first_block->next_block = free_block_list_;
108  first_block->num_free_blocks = (PAGE_SIZE - sizeof(LinkerAllocatorPage*))/block_size_;
109
110  free_block_list_ = first_block;
111
112  page->next = page_list_;
113  page_list_ = page;
114}
115
116LinkerAllocatorPage* LinkerBlockAllocator::find_page(void* block) {
117  if (block == nullptr) {
118    abort();
119  }
120
121  LinkerAllocatorPage* page = page_list_;
122  while (page != nullptr) {
123    const uint8_t* page_ptr = reinterpret_cast<const uint8_t*>(page);
124    if (block >= (page_ptr + sizeof(page->next)) && block < (page_ptr + PAGE_SIZE)) {
125      return page;
126    }
127
128    page = page->next;
129  }
130
131  abort();
132}
133