struct t {
    int a1;
    int a2;
    unsigned char x, y, z, k;
};

__attribute__((__format__(__printf__, 1, 2)))
void doprint(const char *format, ...);

void foo(struct t *t) {
    /* Warns with -Wformat but not with -Wformat -Wformat-signedness */
    doprint("hello %lu\n", t->k);
}