linker/linker_mapped_file_fragment.cpp

/*
 * Copyright (C) 2015 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_mapped_file_fragment.h"
#include "linker_debug.h"

#include <inttypes.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

constexpr off64_t kPageMask = ~static_cast<off64_t>(PAGE_SIZE-1);

static off64_t page_start(off64_t offset) {
  return offset & kPageMask;
}

static bool safe_add(off64_t* out, off64_t a, size_t b) {
  CHECK(a >= 0);
  if (static_cast<uint64_t>(INT64_MAX - a) < b) {
    return false;
  }

  *out = a + b;
  return true;
}

static size_t page_offset(off64_t offset) {
  return static_cast<size_t>(offset & (PAGE_SIZE-1));
}

MappedFileFragment::MappedFileFragment() : map_start_(nullptr), map_size_(0),
                                           data_(nullptr), size_ (0)
{ }

MappedFileFragment::~MappedFileFragment() {
  if (map_start_ != nullptr) {
    munmap(map_start_, map_size_);
  }
}

bool MappedFileFragment::Map(int fd, off64_t base_offset, size_t elf_offset, size_t size) {
  off64_t offset;
  CHECK(safe_add(&offset, base_offset, elf_offset));

  off64_t page_min = page_start(offset);
  off64_t end_offset;

  CHECK(safe_add(&end_offset, offset, size));
  CHECK(safe_add(&end_offset, end_offset, page_offset(offset)));

  size_t map_size = static_cast<size_t>(end_offset - page_min);
  CHECK(map_size >= size);

  uint8_t* map_start = static_cast<uint8_t*>(
                          mmap64(nullptr, map_size, PROT_READ, MAP_PRIVATE, fd, page_min));

  if (map_start == MAP_FAILED) {
    return false;
  }

  map_start_ = map_start;
  map_size_ = map_size;

  data_ = map_start + page_offset(offset);
  size_ = size;

  return true;
}