Macro pgm_get_far_address() from avr/pgmspace.h has a wrong constraint for operand %1: Is must be "ni" (known at compile-time (n) or known ar assembly time or later (i)) instead of "p".

Moreover, the asm is not volatile, hence the "volatile" can be dropped.

The "tmp" should also be recplaced by an identifier from implementation space like __tmp.

Last not least, the macro should come with "extension" so that it will work in strict C mode (and not only with GNU-C which valued blocks are).

Putting everything together, the macro should read

#define pgm_get_far_address(var)                      \
(__extension__({                                      \
    uint_farptr_t __tmp;                              \
                                                      \
    __asm__ (                                         \
            "ldi    %A0, lo8(%1)"           "\n\t"    \
            "ldi    %B0, hi8(%1)"           "\n\t"    \
            "ldi    %C0, hh8(%1)"           "\n\t"    \
            "clr    %D0"                    "\n\t"    \
        : "=d" (__tmp)                                \
        : "ni" (&(var))                               \
    );                                                \
    __tmp;                                            \
}))