Add m-esr52 at 52.6.0

1 files changed, 681 insertions, 0 deletions

diff --git a/mozglue/linker/Mappable.cpp b/mozglue/linker/Mappable.cpp
new file mode 100644
index 000000000..47b883d2d
--- /dev/null
+++ b/mozglue/linker/Mappable.cpp
@@ -0,0 +1,681 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <cstring>
+#include <cstdlib>
+#include <cstdio>
+#include <string>
+
+#include "Mappable.h"
+
+#include "mozilla/UniquePtr.h"
+
+#ifdef ANDROID
+#include <linux/ashmem.h>
+#endif
+#include <sys/stat.h>
+#include <errno.h>
+#include "ElfLoader.h"
+#include "SeekableZStream.h"
+#include "XZStream.h"
+#include "Logging.h"
+
+using mozilla::MakeUnique;
+using mozilla::UniquePtr;
+
+class CacheValidator
+{
+public:
+  CacheValidator(const char* aCachedLibPath, Zip* aZip, Zip::Stream* aStream)
+    : mCachedLibPath(aCachedLibPath)
+  {
+    static const char kChecksumSuffix[] = ".crc";
+
+    mCachedChecksumPath =
+      MakeUnique<char[]>(strlen(aCachedLibPath) + sizeof(kChecksumSuffix));
+    sprintf(mCachedChecksumPath.get(), "%s%s", aCachedLibPath, kChecksumSuffix);
+    DEBUG_LOG("mCachedChecksumPath: %s", mCachedChecksumPath.get());
+
+    mChecksum = aStream->GetCRC32();
+    DEBUG_LOG("mChecksum: %x", mChecksum);
+  }
+
+  // Returns whether the cache is valid and up-to-date.
+  bool IsValid() const
+  {
+    // Validate based on checksum.
+    RefPtr<Mappable> checksumMap = MappableFile::Create(mCachedChecksumPath.get());
+    if (!checksumMap) {
+      // Force caching if checksum is missing in cache.
+      return false;
+    }
+
+    DEBUG_LOG("Comparing %x with %s", mChecksum, mCachedChecksumPath.get());
+    MappedPtr checksumBuf = checksumMap->mmap(nullptr, checksumMap->GetLength(),
+                                              PROT_READ, MAP_PRIVATE, 0);
+    if (checksumBuf == MAP_FAILED) {
+      WARN("Couldn't map %s to validate checksum", mCachedChecksumPath.get());
+      return false;
+    }
+    if (memcmp(checksumBuf, &mChecksum, sizeof(mChecksum))) {
+      return false;
+    }
+    return !access(mCachedLibPath.c_str(), R_OK);
+  }
+
+  // Caches the APK-provided checksum used in future cache validations.
+  void CacheChecksum() const
+  {
+    AutoCloseFD fd(open(mCachedChecksumPath.get(),
+                        O_TRUNC | O_RDWR | O_CREAT | O_NOATIME,
+                        S_IRUSR | S_IWUSR));
+    if (fd == -1) {
+      WARN("Couldn't open %s to update checksum", mCachedChecksumPath.get());
+      return;
+    }
+
+    DEBUG_LOG("Updating checksum %s", mCachedChecksumPath.get());
+
+    const size_t size = sizeof(mChecksum);
+    size_t written = 0;
+    while (written < size) {
+      ssize_t ret = write(fd,
+                          reinterpret_cast<const uint8_t*>(&mChecksum) + written,
+                          size - written);
+      if (ret >= 0) {
+        written += ret;
+      } else if (errno != EINTR) {
+        WARN("Writing checksum %s failed with errno %d",
+             mCachedChecksumPath.get(), errno);
+        break;
+      }
+    }
+  }
+
+private:
+  const std::string mCachedLibPath;
+  UniquePtr<char[]> mCachedChecksumPath;
+  uint32_t mChecksum;
+};
+
+Mappable *
+MappableFile::Create(const char *path)
+{
+  int fd = open(path, O_RDONLY);
+  if (fd != -1)
+    return new MappableFile(fd);
+  return nullptr;
+}
+
+MemoryRange
+MappableFile::mmap(const void *addr, size_t length, int prot, int flags,
+                   off_t offset)
+{
+  MOZ_ASSERT(fd != -1);
+  MOZ_ASSERT(!(flags & MAP_SHARED));
+  flags |= MAP_PRIVATE;
+
+  return MemoryRange::mmap(const_cast<void *>(addr), length, prot, flags,
+                           fd, offset);
+}
+
+void
+MappableFile::finalize()
+{
+  /* Close file ; equivalent to close(fd.forget()) */
+  fd = -1;
+}
+
+size_t
+MappableFile::GetLength() const
+{
+  struct stat st;
+  return fstat(fd, &st) ? 0 : st.st_size;
+}
+
+Mappable *
+MappableExtractFile::Create(const char *name, Zip *zip, Zip::Stream *stream)
+{
+  MOZ_ASSERT(zip && stream);
+
+  const char *cachePath = getenv("MOZ_LINKER_CACHE");
+  if (!cachePath || !*cachePath) {
+    WARN("MOZ_LINKER_EXTRACT is set, but not MOZ_LINKER_CACHE; "
+        "not extracting");
+    return nullptr;
+  }
+
+  // Ensure that the cache dir is private.
+  chmod(cachePath, 0770);
+
+  UniquePtr<char[]> path =
+    MakeUnique<char[]>(strlen(cachePath) + strlen(name) + 2);
+  sprintf(path.get(), "%s/%s", cachePath, name);
+
+  CacheValidator validator(path.get(), zip, stream);
+  if (validator.IsValid()) {
+    DEBUG_LOG("Reusing %s", static_cast<char *>(path.get()));
+    return MappableFile::Create(path.get());
+  }
+  DEBUG_LOG("Extracting to %s", static_cast<char *>(path.get()));
+  AutoCloseFD fd;
+  fd = open(path.get(), O_TRUNC | O_RDWR | O_CREAT | O_NOATIME,
+                        S_IRUSR | S_IWUSR);
+  if (fd == -1) {
+    ERROR("Couldn't open %s to decompress library", path.get());
+    return nullptr;
+  }
+  AutoUnlinkFile file(path.release());
+  if (stream->GetType() == Zip::Stream::DEFLATE) {
+    if (ftruncate(fd, stream->GetUncompressedSize()) == -1) {
+      ERROR("Couldn't ftruncate %s to decompress library", file.get());
+      return nullptr;
+    }
+    /* Map the temporary file for use as inflate buffer */
+    MappedPtr buffer(MemoryRange::mmap(nullptr, stream->GetUncompressedSize(),
+                                       PROT_WRITE, MAP_SHARED, fd, 0));
+    if (buffer == MAP_FAILED) {
+      ERROR("Couldn't map %s to decompress library", file.get());
+      return nullptr;
+    }
+
+    zxx_stream zStream = stream->GetZStream(buffer);
+
+    /* Decompress */
+    if (inflateInit2(&zStream, -MAX_WBITS) != Z_OK) {
+      ERROR("inflateInit failed: %s", zStream.msg);
+      return nullptr;
+    }
+    if (inflate(&zStream, Z_FINISH) != Z_STREAM_END) {
+      ERROR("inflate failed: %s", zStream.msg);
+      return nullptr;
+    }
+    if (inflateEnd(&zStream) != Z_OK) {
+      ERROR("inflateEnd failed: %s", zStream.msg);
+      return nullptr;
+    }
+    if (zStream.total_out != stream->GetUncompressedSize()) {
+      ERROR("File not fully uncompressed! %ld / %d", zStream.total_out,
+          static_cast<unsigned int>(stream->GetUncompressedSize()));
+      return nullptr;
+    }
+  } else if (XZStream::IsXZ(stream->GetBuffer(), stream->GetSize())) {
+    XZStream xzStream(stream->GetBuffer(), stream->GetSize());
+
+    if (!xzStream.Init()) {
+      ERROR("Couldn't initialize XZ decoder");
+      return nullptr;
+    }
+    DEBUG_LOG("XZStream created, compressed=%u, uncompressed=%u",
+              xzStream.Size(), xzStream.UncompressedSize());
+
+    if (ftruncate(fd, xzStream.UncompressedSize()) == -1) {
+      ERROR("Couldn't ftruncate %s to decompress library", file.get());
+      return nullptr;
+    }
+    MappedPtr buffer(MemoryRange::mmap(nullptr, xzStream.UncompressedSize(),
+                                       PROT_WRITE, MAP_SHARED, fd, 0));
+    if (buffer == MAP_FAILED) {
+      ERROR("Couldn't map %s to decompress library", file.get());
+      return nullptr;
+    }
+    const size_t written = xzStream.Decode(buffer, buffer.GetLength());
+    DEBUG_LOG("XZStream decoded %u", written);
+    if (written != buffer.GetLength()) {
+      ERROR("Error decoding XZ file %s", file.get());
+      return nullptr;
+    }
+  } else if (stream->GetType() == Zip::Stream::STORE) {
+    SeekableZStream zStream;
+    if (!zStream.Init(stream->GetBuffer(), stream->GetSize())) {
+      ERROR("Couldn't initialize SeekableZStream for %s", name);
+      return nullptr;
+    }
+    if (ftruncate(fd, zStream.GetUncompressedSize()) == -1) {
+      ERROR("Couldn't ftruncate %s to decompress library", file.get());
+      return nullptr;
+    }
+    MappedPtr buffer(MemoryRange::mmap(nullptr, zStream.GetUncompressedSize(),
+                                       PROT_WRITE, MAP_SHARED, fd, 0));
+    if (buffer == MAP_FAILED) {
+      ERROR("Couldn't map %s to decompress library", file.get());
+      return nullptr;
+    }
+
+    if (!zStream.Decompress(buffer, 0, zStream.GetUncompressedSize())) {
+      ERROR("%s: failed to decompress", name);
+      return nullptr;
+    }
+  } else {
+    return nullptr;
+  }
+
+  validator.CacheChecksum();
+  return new MappableExtractFile(fd.forget(), file.release());
+}
+
+/**
+ * _MappableBuffer is a buffer which content can be mapped at different
+ * locations in the virtual address space.
+ * On Linux, uses a (deleted) temporary file on a tmpfs for sharable content.
+ * On Android, uses ashmem.
+ */
+class _MappableBuffer: public MappedPtr
+{
+public:
+  /**
+   * Returns a _MappableBuffer instance with the given name and the given
+   * length.
+   */
+  static _MappableBuffer *Create(const char *name, size_t length)
+  {
+    AutoCloseFD fd;
+#ifdef ANDROID
+    /* On Android, initialize an ashmem region with the given length */
+    fd = open("/" ASHMEM_NAME_DEF, O_RDWR, 0600);
+    if (fd == -1)
+      return nullptr;
+    char str[ASHMEM_NAME_LEN];
+    strlcpy(str, name, sizeof(str));
+    ioctl(fd, ASHMEM_SET_NAME, str);
+    if (ioctl(fd, ASHMEM_SET_SIZE, length))
+      return nullptr;
+
+    /* The Gecko crash reporter is confused by adjacent memory mappings of
+     * the same file and chances are we're going to map from the same file
+     * descriptor right away. To avoid problems with the crash reporter,
+     * create an empty anonymous page before or after the ashmem mapping,
+     * depending on how mappings grow in the address space.
+     */
+#if defined(__arm__)
+    void *buf = ::mmap(nullptr, length + PAGE_SIZE, PROT_READ | PROT_WRITE,
+                       MAP_SHARED, fd, 0);
+    if (buf != MAP_FAILED) {
+      ::mmap(AlignedEndPtr(reinterpret_cast<char *>(buf) + length, PAGE_SIZE),
+             PAGE_SIZE, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+      DEBUG_LOG("Decompression buffer of size 0x%x in ashmem \"%s\", mapped @%p",
+                length, str, buf);
+      return new _MappableBuffer(fd.forget(), buf, length);
+    }
+#elif defined(__i386__)
+    size_t anon_mapping_length = length + PAGE_SIZE;
+    void *buf = ::mmap(nullptr, anon_mapping_length, PROT_NONE,
+                       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (buf != MAP_FAILED) {
+      char *first_page = reinterpret_cast<char *>(buf);
+      char *map_page = first_page + PAGE_SIZE;
+
+      void *actual_buf = ::mmap(map_page, length, PROT_READ | PROT_WRITE,
+                                MAP_FIXED | MAP_SHARED, fd, 0);
+      if (actual_buf == MAP_FAILED) {
+        ::munmap(buf, anon_mapping_length);
+        DEBUG_LOG("Fixed allocation of decompression buffer at %p failed", map_page);
+        return nullptr;
+      }
+
+      DEBUG_LOG("Decompression buffer of size 0x%x in ashmem \"%s\", mapped @%p",
+                length, str, actual_buf);
+      return new _MappableBuffer(fd.forget(), actual_buf, length);
+    }
+#else
+#error need to add a case for your CPU
+#endif
+#else
+    /* On Linux, use /dev/shm as base directory for temporary files, assuming
+     * it's on tmpfs */
+    /* TODO: check that /dev/shm is tmpfs */
+    char path[256];
+    sprintf(path, "/dev/shm/%s.XXXXXX", name);
+    fd = mkstemp(path);
+    if (fd == -1)
+      return nullptr;
+    unlink(path);
+    ftruncate(fd, length);
+
+    void *buf = ::mmap(nullptr, length, PROT_READ | PROT_WRITE,
+                       MAP_SHARED, fd, 0);
+    if (buf != MAP_FAILED) {
+      DEBUG_LOG("Decompression buffer of size %ld in \"%s\", mapped @%p",
+                length, path, buf);
+      return new _MappableBuffer(fd.forget(), buf, length);
+    }
+#endif
+    return nullptr;
+  }
+
+  void *mmap(const void *addr, size_t length, int prot, int flags, off_t offset)
+  {
+    MOZ_ASSERT(fd != -1);
+#ifdef ANDROID
+    /* Mapping ashmem MAP_PRIVATE is like mapping anonymous memory, even when
+     * there is content in the ashmem */
+    if (flags & MAP_PRIVATE) {
+      flags &= ~MAP_PRIVATE;
+      flags |= MAP_SHARED;
+    }
+#endif
+    return ::mmap(const_cast<void *>(addr), length, prot, flags, fd, offset);
+  }
+
+#ifdef ANDROID
+  ~_MappableBuffer() {
+    /* Free the additional page we allocated. See _MappableBuffer::Create */
+#if defined(__arm__)
+    ::munmap(AlignedEndPtr(*this + GetLength(), PAGE_SIZE), PAGE_SIZE);
+#elif defined(__i386__)
+    ::munmap(*this - PAGE_SIZE, GetLength() + PAGE_SIZE);
+#else
+#error need to add a case for your CPU
+#endif
+  }
+#endif
+
+private:
+  _MappableBuffer(int fd, void *buf, size_t length)
+  : MappedPtr(buf, length), fd(fd) { }
+
+  /* File descriptor for the temporary file or ashmem */
+  AutoCloseFD fd;
+};
+
+
+Mappable *
+MappableDeflate::Create(const char *name, Zip *zip, Zip::Stream *stream)
+{
+  MOZ_ASSERT(stream->GetType() == Zip::Stream::DEFLATE);
+  _MappableBuffer *buf = _MappableBuffer::Create(name, stream->GetUncompressedSize());
+  if (buf)
+    return new MappableDeflate(buf, zip, stream);
+  return nullptr;
+}
+
+MappableDeflate::MappableDeflate(_MappableBuffer *buf, Zip *zip,
+                                 Zip::Stream *stream)
+: zip(zip), buffer(buf), zStream(stream->GetZStream(*buf)) { }
+
+MappableDeflate::~MappableDeflate() { }
+
+MemoryRange
+MappableDeflate::mmap(const void *addr, size_t length, int prot, int flags, off_t offset)
+{
+  MOZ_ASSERT(buffer);
+  MOZ_ASSERT(!(flags & MAP_SHARED));
+  flags |= MAP_PRIVATE;
+
+  /* The deflate stream is uncompressed up to the required offset + length, if
+   * it hasn't previously been uncompressed */
+  ssize_t missing = offset + length + zStream.avail_out - buffer->GetLength();
+  if (missing > 0) {
+    uInt avail_out = zStream.avail_out;
+    zStream.avail_out = missing;
+    if ((*buffer == zStream.next_out) &&
+        (inflateInit2(&zStream, -MAX_WBITS) != Z_OK)) {
+      ERROR("inflateInit failed: %s", zStream.msg);
+      return MemoryRange(MAP_FAILED, 0);
+    }
+    int ret = inflate(&zStream, Z_SYNC_FLUSH);
+    if (ret < 0) {
+      ERROR("inflate failed: %s", zStream.msg);
+      return MemoryRange(MAP_FAILED, 0);
+    }
+    if (ret == Z_NEED_DICT) {
+      ERROR("zstream requires a dictionary. %s", zStream.msg);
+      return MemoryRange(MAP_FAILED, 0);
+    }
+    zStream.avail_out = avail_out - missing + zStream.avail_out;
+    if (ret == Z_STREAM_END) {
+      if (inflateEnd(&zStream) != Z_OK) {
+        ERROR("inflateEnd failed: %s", zStream.msg);
+        return MemoryRange(MAP_FAILED, 0);
+      }
+      if (zStream.total_out != buffer->GetLength()) {
+        ERROR("File not fully uncompressed! %ld / %d", zStream.total_out,
+            static_cast<unsigned int>(buffer->GetLength()));
+        return MemoryRange(MAP_FAILED, 0);
+      }
+    }
+  }
+#if defined(ANDROID) && defined(__arm__)
+  if (prot & PROT_EXEC) {
+    /* We just extracted data that may be executed in the future.
+     * We thus need to ensure Instruction and Data cache coherency. */
+    DEBUG_LOG("cacheflush(%p, %p)", *buffer + offset, *buffer + (offset + length));
+    cacheflush(reinterpret_cast<uintptr_t>(*buffer + offset),
+               reinterpret_cast<uintptr_t>(*buffer + (offset + length)), 0);
+  }
+#endif
+
+  return MemoryRange(buffer->mmap(addr, length, prot, flags, offset), length);
+}
+
+void
+MappableDeflate::finalize()
+{
+  /* Free zlib internal buffers */
+  inflateEnd(&zStream);
+  /* Free decompression buffer */
+  buffer = nullptr;
+  /* Remove reference to Zip archive */
+  zip = nullptr;
+}
+
+size_t
+MappableDeflate::GetLength() const
+{
+  return buffer->GetLength();
+}
+
+Mappable *
+MappableSeekableZStream::Create(const char *name, Zip *zip,
+                                Zip::Stream *stream)
+{
+  MOZ_ASSERT(stream->GetType() == Zip::Stream::STORE);
+  UniquePtr<MappableSeekableZStream> mappable(new MappableSeekableZStream(zip));
+
+  pthread_mutexattr_t recursiveAttr;
+  pthread_mutexattr_init(&recursiveAttr);
+  pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);
+
+  if (pthread_mutex_init(&mappable->mutex, &recursiveAttr))
+    return nullptr;
+
+  if (!mappable->zStream.Init(stream->GetBuffer(), stream->GetSize()))
+    return nullptr;
+
+  mappable->buffer.reset(_MappableBuffer::Create(name,
+                              mappable->zStream.GetUncompressedSize()));
+  if (!mappable->buffer)
+    return nullptr;
+
+  mappable->chunkAvail = MakeUnique<unsigned char[]>(mappable->zStream.GetChunksNum());
+
+  return mappable.release();
+}
+
+MappableSeekableZStream::MappableSeekableZStream(Zip *zip)
+: zip(zip), chunkAvailNum(0) { }
+
+MappableSeekableZStream::~MappableSeekableZStream()
+{
+  pthread_mutex_destroy(&mutex);
+}
+
+MemoryRange
+MappableSeekableZStream::mmap(const void *addr, size_t length, int prot,
+                              int flags, off_t offset)
+{
+  /* Map with PROT_NONE so that accessing the mapping would segfault, and
+   * bring us to ensure() */
+  void *res = buffer->mmap(addr, length, PROT_NONE, flags, offset);
+  if (res == MAP_FAILED)
+    return MemoryRange(MAP_FAILED, 0);
+
+  /* Store the mapping, ordered by offset and length */
+  std::vector<LazyMap>::reverse_iterator it;
+  for (it = lazyMaps.rbegin(); it < lazyMaps.rend(); ++it) {
+    if ((it->offset < offset) ||
+        ((it->offset == offset) && (it->length < length)))
+      break;
+  }
+  LazyMap map = { res, length, prot, offset };
+  lazyMaps.insert(it.base(), map);
+  return MemoryRange(res, length);
+}
+
+void
+MappableSeekableZStream::munmap(void *addr, size_t length)
+{
+  std::vector<LazyMap>::iterator it;
+  for (it = lazyMaps.begin(); it < lazyMaps.end(); ++it)
+    if ((it->addr = addr) && (it->length == length)) {
+      lazyMaps.erase(it);
+      ::munmap(addr, length);
+      return;
+    }
+  MOZ_CRASH("munmap called with unknown mapping");
+}
+
+void
+MappableSeekableZStream::finalize() { }
+
+bool
+MappableSeekableZStream::ensure(const void *addr)
+{
+  DEBUG_LOG("ensure @%p", addr);
+  const void *addrPage = PageAlignedPtr(addr);
+  /* Find the mapping corresponding to the given page */
+  std::vector<LazyMap>::iterator map;
+  for (map = lazyMaps.begin(); map < lazyMaps.end(); ++map) {
+    if (map->Contains(addrPage))
+      break;
+  }
+  if (map == lazyMaps.end())
+    return false;
+
+  /* Find corresponding chunk */
+  off_t mapOffset = map->offsetOf(addrPage);
+  off_t chunk = mapOffset / zStream.GetChunkSize();
+
+  /* In the typical case, we just need to decompress the chunk entirely. But
+   * when the current mapping ends in the middle of the chunk, we want to
+   * stop at the end of the corresponding page.
+   * However, if another mapping needs the last part of the chunk, we still
+   * need to continue. As mappings are ordered by offset and length, we don't
+   * need to scan the entire list of mappings.
+   * It is safe to run through lazyMaps here because the linker is never
+   * going to call mmap (which adds lazyMaps) while this function is
+   * called. */
+  size_t length = zStream.GetChunkSize(chunk);
+  off_t chunkStart = chunk * zStream.GetChunkSize();
+  off_t chunkEnd = chunkStart + length;
+  std::vector<LazyMap>::iterator it;
+  for (it = map; it < lazyMaps.end(); ++it) {
+    if (chunkEnd <= it->endOffset())
+      break;
+  }
+  if ((it == lazyMaps.end()) || (chunkEnd > it->endOffset())) {
+    /* The mapping "it" points at now is past the interesting one */
+    --it;
+    length = it->endOffset() - chunkStart;
+  }
+
+  length = PageAlignedSize(length);
+
+  /* The following lock can be re-acquired by the thread holding it.
+   * If this happens, it means the following code is interrupted somehow by
+   * some signal, and ends up retriggering a chunk decompression for the
+   * same MappableSeekableZStream.
+   * If the chunk to decompress is different the second time, then everything
+   * is safe as the only common data touched below is chunkAvailNum, and it is
+   * atomically updated (leaving out any chance of an interruption while it is
+   * updated affecting the result). If the chunk to decompress is the same, the
+   * worst thing that can happen is chunkAvailNum being incremented one too
+   * many times, which doesn't affect functionality. The chances of it
+   * happening being pretty slim, and the effect being harmless, we can just
+   * ignore the issue. Other than that, we'd just be wasting time decompressing
+   * the same chunk twice. */
+  AutoLock lock(&mutex);
+
+  /* The very first page is mapped and accessed separately of the rest, and
+   * as such, only the first page of the first chunk is decompressed this way.
+   * When we fault in the remaining pages of that chunk, we want to decompress
+   * the complete chunk again. Short of doing that, we would end up with
+   * no data between PageSize() and chunkSize, which would effectively corrupt
+   * symbol resolution in the underlying library. */
+  if (chunkAvail[chunk] < PageNumber(length)) {
+    if (!zStream.DecompressChunk(*buffer + chunkStart, chunk, length))
+      return false;
+
+#if defined(ANDROID) && defined(__arm__)
+    if (map->prot & PROT_EXEC) {
+      /* We just extracted data that may be executed in the future.
+       * We thus need to ensure Instruction and Data cache coherency. */
+      DEBUG_LOG("cacheflush(%p, %p)", *buffer + chunkStart, *buffer + (chunkStart + length));
+      cacheflush(reinterpret_cast<uintptr_t>(*buffer + chunkStart),
+                 reinterpret_cast<uintptr_t>(*buffer + (chunkStart + length)), 0);
+    }
+#endif
+    /* Only count if we haven't already decompressed parts of the chunk */
+    if (chunkAvail[chunk] == 0)
+      chunkAvailNum++;
+
+    chunkAvail[chunk] = PageNumber(length);
+  }
+
+  /* Flip the chunk mapping protection to the recorded flags. We could
+   * also flip the protection for other mappings of the same chunk,
+   * but it's easier to skip that and let further segfaults call
+   * ensure again. */
+  const void *chunkAddr = reinterpret_cast<const void *>
+                          (reinterpret_cast<uintptr_t>(addrPage)
+                           - mapOffset % zStream.GetChunkSize());
+  const void *chunkEndAddr = reinterpret_cast<const void *>
+                             (reinterpret_cast<uintptr_t>(chunkAddr) + length);
+  
+  const void *start = std::max(map->addr, chunkAddr);
+  const void *end = std::min(map->end(), chunkEndAddr);
+  length = reinterpret_cast<uintptr_t>(end)
+           - reinterpret_cast<uintptr_t>(start);
+
+  if (mprotect(const_cast<void *>(start), length, map->prot) == 0) {
+    DEBUG_LOG("mprotect @%p, 0x%" PRIxSize ", 0x%x", start, length, map->prot);
+    return true;
+  }
+
+  ERROR("mprotect @%p, 0x%" PRIxSize ", 0x%x failed with errno %d",
+      start, length, map->prot, errno);
+  return false;
+}
+
+void
+MappableSeekableZStream::stats(const char *when, const char *name) const
+{
+  size_t nEntries = zStream.GetChunksNum();
+  DEBUG_LOG("%s: %s; %" PRIdSize "/%" PRIdSize " chunks decompressed",
+            name, when, static_cast<size_t>(chunkAvailNum), nEntries);
+
+  size_t len = 64;
+  UniquePtr<char[]> map = MakeUnique<char[]>(len + 3);
+  map[0] = '[';
+
+  for (size_t i = 0, j = 1; i < nEntries; i++, j++) {
+    map[j] = chunkAvail[i] ? '*' : '_';
+    if ((j == len) || (i == nEntries - 1)) {
+      map[j + 1] = ']';
+      map[j + 2] = '\0';
+      DEBUG_LOG("%s", static_cast<char *>(map.get()));
+      j = 0;
+    }
+  }
+}
+
+size_t
+MappableSeekableZStream::GetLength() const
+{
+  return buffer->GetLength();
+}