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