Class Module

tools/webassembly.py:192–638

Extremely minimal wasm module reader. Currently only used for parsing the dylink section.

class Module:
  """Extremely minimal wasm module reader.

  Currently only used for parsing the dylink section.
  """

  def __init__(self, filename):
    self.buf = None # Set this before FS calls below in case they throw.
    self.filename = filename
    self.size = os.path.getsize(filename)
    self.buf = open(filename, 'rb')
    magic = self.buf.read(4)
    version = self.buf.read(4)
    if magic != MAGIC or version != VERSION:
      raise InvalidWasmError(f'{filename} is not a valid wasm file')
    self._cache = {}

  def __del__(self):
    assert not self.buf, '`__exit__` should have already been called, please use context manager'

  def __enter__(self):
    return self

  def __exit__(self, _exc_type, _exc_val, _exc_tb):
    if self.buf:
      self.buf.close()
      self.buf = None

  def read_at(self, offset, count):
    self.buf.seek(offset)
    return self.buf.read(count)

  def read_byte(self):
    return self.buf.read(1)[0]

  def read_uleb(self):
    return read_uleb(self.buf)

  def read_sleb(self):
    return read_sleb(self.buf)

  def read_string(self):
    size = self.read_uleb()
    return self.buf.read(size).decode('utf-8')

  def read_limits(self):
    flags = self.read_byte()
    initial = self.read_uleb()
    maximum = 0
    if flags & LIMITS_HAS_MAX:
      maximum = self.read_uleb()
    return Limits(flags, initial, maximum)

  def read_type(self):
    return Type(self.read_uleb())

  def read_init(self):
    code = []