Function set_initial_memory

tools/link.py:524–569

()

def set_initial_memory():
  user_specified_initial_heap = 'INITIAL_HEAP' in user_settings

  # INITIAL_HEAP cannot be used when the memory object is created in JS: we don't know
  # the size of static data here and thus the total initial memory size.
  if settings.IMPORTED_MEMORY:
    if user_specified_initial_heap:
      # Some of these could (and should) be implemented.
      exit_with_error('INITIAL_HEAP is currently not compatible with IMPORTED_MEMORY')
    # The default for imported memory is to fall back to INITIAL_MEMORY.
    settings.INITIAL_HEAP = -1

  if not user_specified_initial_heap:
    # For backwards compatibility, we will only use INITIAL_HEAP by default when the user
    # specified neither INITIAL_MEMORY nor MAXIMUM_MEMORY. Both place an upper bounds on
    # the overall initial linear memory (stack + static data + heap), and we do not know
    # the size of static data at this stage. Setting any non-zero initial heap value in
    # this scenario would risk pushing users over the limit they have set.
    user_specified_initial = settings.INITIAL_MEMORY != -1
    user_specified_maximum = 'MAXIMUM_MEMORY' in user_settings or 'WASM_MEM_MAX' in user_settings or 'BINARYEN_MEM_MAX' in user_settings
    if user_specified_initial or user_specified_maximum:
      settings.INITIAL_HEAP = -1

  # Apply the default if we are going with INITIAL_MEMORY.
  if settings.INITIAL_HEAP == -1 and settings.INITIAL_MEMORY == -1:
    default_setting('INITIAL_MEMORY', 16 * 1024 * 1024)

  def check_memory_setting(setting):
    if settings[setting] % webassembly.WASM_PAGE_SIZE != 0:
      exit_with_error(f'{setting} must be a multiple of WebAssembly page size (64KiB), was {settings[setting]}')
    if settings[setting] >= 2**53:
      exit_with_error(f'{setting} must be smaller than 2^53 bytes due to JS Numbers (doubles) being used to hold pointer addresses in JS side')

  # Due to the aforementioned lack of knowledge about the static data size, we delegate
  # checking the overall consistency of these settings to wasm-ld.
  if settings.INITIAL_HEAP != -1:
    check_memory_setting('INITIAL_HEAP')

  if settings.INITIAL_MEMORY != -1:
    check_memory_setting('INITIAL_MEMORY')
    if settings.INITIAL_MEMORY < settings.STACK_SIZE:
      exit_with_error(f'INITIAL_MEMORY must be larger than STACK_SIZE, was {settings.INITIAL_MEMORY} (STACK_SIZE={settings.STACK_SIZE})')

  check_memory_setting('MAXIMUM_MEMORY')
  if settings.MEMORY_GROWTH_LINEAR_STEP != -1:
    check_memory_setting('MEMORY_GROWTH_LINEAR_STEP')


# Set an upper estimate of what MAXIMUM_MEMORY should be. Take note that this value