https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85719
--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> --- IMO the documentation on "io", "io_low" and "address" has improved. Maybe it is clearer now? There's also an example what code will be generated for attribute "address". https://gcc.gnu.org/onlinedocs/gcc/AVR-Variable-Attributes.html#index-io-variable-attribute_002c-AVR
