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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 #include "linker_allocator.h"
     17 #include <inttypes.h>
     18 #include <sys/mman.h>
     19 #include <unistd.h>
     20 
     21 #include "private/bionic_prctl.h"
     22 
     23 struct LinkerAllocatorPage {
     24   LinkerAllocatorPage* next;
     25   uint8_t bytes[PAGE_SIZE-sizeof(LinkerAllocatorPage*)];
     26 };
     27 
     28 struct FreeBlockInfo {
     29   void* next_block;
     30   size_t num_free_blocks;
     31 };
     32 
     33 LinkerBlockAllocator::LinkerBlockAllocator(size_t block_size)
     34   : block_size_(block_size < sizeof(FreeBlockInfo) ? sizeof(FreeBlockInfo) : block_size),
     35     page_list_(nullptr),
     36     free_block_list_(nullptr)
     37 {}
     38 
     39 void* LinkerBlockAllocator::alloc() {
     40   if (free_block_list_ == nullptr) {
     41     create_new_page();
     42   }
     43 
     44   FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(free_block_list_);
     45   if (block_info->num_free_blocks > 1) {
     46     FreeBlockInfo* next_block_info = reinterpret_cast<FreeBlockInfo*>(
     47       reinterpret_cast<char*>(free_block_list_) + block_size_);
     48     next_block_info->next_block = block_info->next_block;
     49     next_block_info->num_free_blocks = block_info->num_free_blocks - 1;
     50     free_block_list_ = next_block_info;
     51   } else {
     52     free_block_list_ = block_info->next_block;
     53   }
     54 
     55   memset(block_info, 0, block_size_);
     56 
     57   return block_info;
     58 }
     59 
     60 void LinkerBlockAllocator::free(void* block) {
     61   if (block == nullptr) {
     62     return;
     63   }
     64 
     65   LinkerAllocatorPage* page = find_page(block);
     66 
     67   if (page == nullptr) {
     68     abort();
     69   }
     70 
     71   ssize_t offset = reinterpret_cast<uint8_t*>(block) - page->bytes;
     72 
     73   if (offset % block_size_ != 0) {
     74     abort();
     75   }
     76 
     77   memset(block, 0, block_size_);
     78 
     79   FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(block);
     80 
     81   block_info->next_block = free_block_list_;
     82   block_info->num_free_blocks = 1;
     83 
     84   free_block_list_ = block_info;
     85 }
     86 
     87 void LinkerBlockAllocator::protect_all(int prot) {
     88   for (LinkerAllocatorPage* page = page_list_; page != nullptr; page = page->next) {
     89     if (mprotect(page, PAGE_SIZE, prot) == -1) {
     90       abort();
     91     }
     92   }
     93 }
     94 
     95 void LinkerBlockAllocator::create_new_page() {
     96   LinkerAllocatorPage* page = reinterpret_cast<LinkerAllocatorPage*>(mmap(nullptr, PAGE_SIZE,
     97       PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0));
     98   if (page == MAP_FAILED) {
     99     abort(); // oom
    100   }
    101 
    102   prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, page, PAGE_SIZE, "linker_alloc");
    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 
    116 LinkerAllocatorPage* 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