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 #include "linker_block_allocator.h"
18 #include <inttypes.h>
19 #include <string.h>
20 #include <sys/mman.h>
21 #include <unistd.h>
22
23 #include "private/bionic_prctl.h"
24
25 struct LinkerBlockAllocatorPage {
26 LinkerBlockAllocatorPage* next;
27 uint8_t bytes[PAGE_SIZE-sizeof(LinkerBlockAllocatorPage*)];
28 };
29
30 struct FreeBlockInfo {
31 void* next_block;
32 size_t num_free_blocks;
33 };
34
LinkerBlockAllocator(size_t block_size)35 LinkerBlockAllocator::LinkerBlockAllocator(size_t block_size)
36 : block_size_(block_size < sizeof(FreeBlockInfo) ? sizeof(FreeBlockInfo) : block_size),
37 page_list_(nullptr),
38 free_block_list_(nullptr)
39 {}
40
alloc()41 void* LinkerBlockAllocator::alloc() {
42 if (free_block_list_ == nullptr) {
43 create_new_page();
44 }
45
46 FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(free_block_list_);
47 if (block_info->num_free_blocks > 1) {
48 FreeBlockInfo* next_block_info = reinterpret_cast<FreeBlockInfo*>(
49 reinterpret_cast<char*>(free_block_list_) + block_size_);
50 next_block_info->next_block = block_info->next_block;
51 next_block_info->num_free_blocks = block_info->num_free_blocks - 1;
52 free_block_list_ = next_block_info;
53 } else {
54 free_block_list_ = block_info->next_block;
55 }
56
57 memset(block_info, 0, block_size_);
58
59 return block_info;
60 }
61
free(void * block)62 void LinkerBlockAllocator::free(void* block) {
63 if (block == nullptr) {
64 return;
65 }
66
67 LinkerBlockAllocatorPage* page = find_page(block);
68
69 if (page == nullptr) {
70 abort();
71 }
72
73 ssize_t offset = reinterpret_cast<uint8_t*>(block) - page->bytes;
74
75 if (offset % block_size_ != 0) {
76 abort();
77 }
78
79 memset(block, 0, block_size_);
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
protect_all(int prot)89 void LinkerBlockAllocator::protect_all(int prot) {
90 for (LinkerBlockAllocatorPage* page = page_list_; page != nullptr; page = page->next) {
91 if (mprotect(page, PAGE_SIZE, prot) == -1) {
92 abort();
93 }
94 }
95 }
96
create_new_page()97 void LinkerBlockAllocator::create_new_page() {
98 LinkerBlockAllocatorPage* page = reinterpret_cast<LinkerBlockAllocatorPage*>(
99 mmap(nullptr, PAGE_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0));
100
101 if (page == MAP_FAILED) {
102 abort(); // oom
103 }
104
105 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, page, PAGE_SIZE, "linker_alloc");
106
107 memset(page, 0, PAGE_SIZE);
108
109 FreeBlockInfo* first_block = reinterpret_cast<FreeBlockInfo*>(page->bytes);
110 first_block->next_block = free_block_list_;
111 first_block->num_free_blocks = (PAGE_SIZE - sizeof(LinkerBlockAllocatorPage*))/block_size_;
112
113 free_block_list_ = first_block;
114
115 page->next = page_list_;
116 page_list_ = page;
117 }
118
find_page(void * block)119 LinkerBlockAllocatorPage* LinkerBlockAllocator::find_page(void* block) {
120 if (block == nullptr) {
121 abort();
122 }
123
124 LinkerBlockAllocatorPage* page = page_list_;
125 while (page != nullptr) {
126 const uint8_t* page_ptr = reinterpret_cast<const uint8_t*>(page);
127 if (block >= (page_ptr + sizeof(page->next)) && block < (page_ptr + PAGE_SIZE)) {
128 return page;
129 }
130
131 page = page->next;
132 }
133
134 abort();
135 }
136