Refactor linker allocator

Makes it reusable for different fixed sized and not very
big structures (<PAGE_SIZE).

Change-Id: Id5ec13fc6541b1935ef7fe3671c22b98685abbae

linker/linker_allocator.cpp

@@ -0,0 +1,142 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "linker_allocator.h"
+#include <inttypes.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+struct LinkerAllocatorPage {
+  LinkerAllocatorPage* next;
+  uint8_t bytes[PAGE_SIZE-sizeof(LinkerAllocatorPage*)];
+};
+
+struct FreeBlockInfo {
+  void* next_block;
+  size_t num_free_blocks;
+};
+
+LinkerBlockAllocator::LinkerBlockAllocator()
+  : block_size_(0),
+    page_list_(nullptr),
+    free_block_list_(nullptr)
+{}
+
+void LinkerBlockAllocator::init(size_t block_size) {
+  block_size_ = block_size < sizeof(FreeBlockInfo) ? sizeof(FreeBlockInfo) : block_size;
+}
+
+
+void* LinkerBlockAllocator::alloc() {
+  if (free_block_list_ == nullptr) {
+    create_new_page();
+  } else {
+    protect_page(free_block_list_, PROT_READ | PROT_WRITE);
+  }
+
+  FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(free_block_list_);
+  if (block_info->num_free_blocks > 1) {
+    FreeBlockInfo* next_block_info = reinterpret_cast<FreeBlockInfo*>(
+      reinterpret_cast<char*>(free_block_list_) + block_size_);
+    next_block_info->next_block = block_info->next_block;
+    next_block_info->num_free_blocks = block_info->num_free_blocks - 1;
+    free_block_list_ = next_block_info;
+  } else {
+    free_block_list_ = block_info->next_block;
+  }
+
+  block_info->next_block = nullptr;
+  block_info->num_free_blocks = 0;
+
+  return block_info;
+}
+
+void LinkerBlockAllocator::free(void* block) {
+  if (block == nullptr) {
+    return;
+  }
+
+  LinkerAllocatorPage* page = find_page(block);
+
+  if (page == nullptr) {
+    abort();
+  }
+
+  ssize_t offset = reinterpret_cast<uint8_t*>(block) - page->bytes;
+
+  if (offset % block_size_ != 0) {
+    abort();
+  }
+
+  FreeBlockInfo* block_info = reinterpret_cast<FreeBlockInfo*>(block);
+
+  protect_page(block_info, PROT_READ | PROT_WRITE);
+  block_info->next_block = free_block_list_;
+  block_info->num_free_blocks = 1;
+  protect_page(block_info, PROT_READ);
+
+  free_block_list_ = block_info;
+}
+
+void LinkerBlockAllocator::protect_all(int prot) {
+  for (LinkerAllocatorPage* page = page_list_; page != nullptr; page = page->next) {
+    if (mprotect(page, PAGE_SIZE, prot) == -1) {
+      abort();
+    }
+  }
+}
+
+void LinkerBlockAllocator::protect_page(void* block, int prot) {
+  LinkerAllocatorPage* page = find_page(block);
+  if (page == nullptr || mprotect(page, PAGE_SIZE, prot) == -1) {
+    abort();
+  }
+}
+
+
+void LinkerBlockAllocator::create_new_page() {
+  LinkerAllocatorPage* page = reinterpret_cast<LinkerAllocatorPage*>(mmap(nullptr, PAGE_SIZE,
+      PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0));
+  if (page == MAP_FAILED) {
+    abort(); // oom
+  }
+
+  FreeBlockInfo* first_block = reinterpret_cast<FreeBlockInfo*>(page->bytes);
+  first_block->next_block = free_block_list_;
+  first_block->num_free_blocks = (PAGE_SIZE - sizeof(LinkerAllocatorPage*))/block_size_;
+
+  free_block_list_ = first_block;
+
+  page->next = page_list_;
+  page_list_ = page;
+}
+
+LinkerAllocatorPage* LinkerBlockAllocator::find_page(void* block) {
+  if (block == nullptr) {
+    abort();
+  }
+
+  LinkerAllocatorPage* page = page_list_;
+  const uint8_t* page_ptr = reinterpret_cast<const uint8_t*>(page);
+  while (page != nullptr) {
+    if (block >= (page_ptr + sizeof(page->next)) && block < (page_ptr + PAGE_SIZE)) {
+      return page;
+    }
+
+    page = page->next;
+  }
+
+  abort();
+}