code: def com_adobe_fonts_check_cff2_call_depth(ttFont):
      
      any_failures = False
      cff = ttFont['CFF2'].cff
  
      for top_dict in cff.topDictIndex:
          for fd_index, font_dict in enumerate(top_dict.FDArray):
              if hasattr(font_dict, 'Private'):
                  private_dict = font_dict.Private
              else:
                  private_dict = None
              failed = yield from \
                  _check_call_depth(top_dict, private_dict, fd_index)
              any_failures = any_failures or failed
  
      if not any_failures:
          yield PASS, 'Maximum call depth not exceeded.'
docs: Is the CFF2 subr/gsubr call depth > 10?