On Mon, Oct 19, 2015 at 12:11 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Monday 19 October 2015 09:34:15 Geert Uytterhoeven wrote: >> On Wed, Oct 7, 2015 at 1:23 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> > static __inline__ int atomic64_add_unless(atomic64_t *v, long a, long u) >> > >> > which truncates the result to 32 bit. >> >> Woops. >> >> See also my unanswered question in "atomic64 on 32-bit vs 64-bit (was: >> Re: Add virtio gpu driver.)", which is still valid: >> https://lkml.org/lkml/2015/6/28/18 >> > > Regarding your question of > >> Instead of sprinkling casts, is there any good reason why atomic64_read() >> and atomic64_t aren't "long long" everywhere, cfr. u64? > > > I assume the answer is that some (all?) 64-bit architectures intentionally > return 'long' here, in order for atomic_long_read() to return 'long' on > all architectures, given the definitions from > include/asm-generic/atomic-long.h > > We would have to either change those, or we have to pick between > atomic_long_* or atomic64_* to have a consistent return type. I guess the main reason is this comment in include/asm-generic/atomic-long.h, which I hadn't noticed before: * Casts for parameters are avoided for existing atomic functions in order to * avoid issues with cast-as-lval under gcc 4.x and other limitations that the * macros of a platform may have. Still, it's a pity, as printing atomic_64 is one more place where casts are needed in callers. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
