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 // the multiplier should be power of 2
round_up(size_t size,size_t multiplier)26 static constexpr size_t round_up(size_t size, size_t multiplier) {
27 return (size + (multiplier - 1)) & ~(multiplier-1);
28 }
29
30 struct LinkerBlockAllocatorPage {
31 LinkerBlockAllocatorPage* next;
32 uint8_t bytes[PAGE_SIZE - 16] __attribute__((aligned(16)));
33 };
34
35 struct FreeBlockInfo {
36 void* next_block;
37 size_t num_free_blocks;
38 };
39
LinkerBlockAllocator(size_t block_size)40 LinkerBlockAllocator::LinkerBlockAllocator(size_t block_size)
41 : block_size_(
42 round_up(block_size < sizeof(FreeBlockInfo) ? sizeof(FreeBlockInfo) : block_size, 16)),
43 page_list_(nullptr),
44 free_block_list_(nullptr)
45 {}
46
alloc()47 void* LinkerBlockAllocator::alloc() {
48 if (free_block_list_ == nullptr) {
49 create_new_page();
50 }
51
52 FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(free_block_list_);
53 if (block_info->num_free_blocks > 1) {
54 FreeBlockInfo* next_block_info = reinterpret_cast<FreeBlockInfo*>(
55 reinterpret_cast<char*>(free_block_list_) + block_size_);
56 next_block_info->next_block = block_info->next_block;
57 next_block_info->num_free_blocks = block_info->num_free_blocks - 1;
58 free_block_list_ = next_block_info;
59 } else {
60 free_block_list_ = block_info->next_block;
61 }
62
63 memset(block_info, 0, block_size_);
64
65 return block_info;
66 }
67
free(void * block)68 void LinkerBlockAllocator::free(void* block) {
69 if (block == nullptr) {
70 return;
71 }
72
73 LinkerBlockAllocatorPage* page = find_page(block);
74
75 if (page == nullptr) {
76 abort();
77 }
78
79 ssize_t offset = reinterpret_cast<uint8_t*>(block) - page->bytes;
80
81 if (offset % block_size_ != 0) {
82 abort();
83 }
84
85 memset(block, 0, block_size_);
86
87 FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(block);
88
89 block_info->next_block = free_block_list_;
90 block_info->num_free_blocks = 1;
91
92 free_block_list_ = block_info;
93 }
94
protect_all(int prot)95 void LinkerBlockAllocator::protect_all(int prot) {
96 for (LinkerBlockAllocatorPage* page = page_list_; page != nullptr; page = page->next) {
97 if (mprotect(page, PAGE_SIZE, prot) == -1) {
98 abort();
99 }
100 }
101 }
102
create_new_page()103 void LinkerBlockAllocator::create_new_page() {
104 static_assert(sizeof(LinkerBlockAllocatorPage) == PAGE_SIZE,
105 "Invalid sizeof(LinkerBlockAllocatorPage)");
106
107 LinkerBlockAllocatorPage* page = reinterpret_cast<LinkerBlockAllocatorPage*>(
108 mmap(nullptr, PAGE_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0));
109
110 if (page == MAP_FAILED) {
111 abort(); // oom
112 }
113
114 prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, page, PAGE_SIZE, "linker_alloc");
115
116 memset(page, 0, PAGE_SIZE);
117
118 FreeBlockInfo* first_block = reinterpret_cast<FreeBlockInfo*>(page->bytes);
119 first_block->next_block = free_block_list_;
120 first_block->num_free_blocks = (PAGE_SIZE - sizeof(LinkerBlockAllocatorPage*))/block_size_;
121
122 free_block_list_ = first_block;
123
124 page->next = page_list_;
125 page_list_ = page;
126 }
127
find_page(void * block)128 LinkerBlockAllocatorPage* LinkerBlockAllocator::find_page(void* block) {
129 if (block == nullptr) {
130 abort();
131 }
132
133 LinkerBlockAllocatorPage* page = page_list_;
134 while (page != nullptr) {
135 const uint8_t* page_ptr = reinterpret_cast<const uint8_t*>(page);
136 if (block >= (page_ptr + sizeof(page->next)) && block < (page_ptr + PAGE_SIZE)) {
137 return page;
138 }
139
140 page = page->next;
141 }
142
143 abort();
144 }
145