On Thu, Mar 06, 2025 at 06:22:33PM +0900, Vincent Mailhol wrote: > On 06/03/2025 at 04:45, Andy Shevchenko wrote: > >>> But GENMASK_U128() becomes a special case now. > >>> The 128-bit GENMASK is unsued, but it's exported in uapi. Is there any > >>> simple way to end up with a common implementation for all fixed-type > >>> GENMASKs? > >> > >> What bothers me is that the 128 bit types are not something available on > >> all architectures, c.f. the CONFIG_ARCH_SUPPORTS_INT128. So, I would > >> need a U128() equivalent to the ULL() but which does not break on > >> architectures which do not support 128 bits integers. > >> > >> This is where I am stuck. If someone can guide me on how to write a > >> robust U128() macro, then I think the common implementation could be > >> feasible. > > > > I think we may leave that U128 stuff alone for now. > > I found the solution! The trick is to use type_max() from overflow.h. > > With this, GENMASK_TYPE() becomes: > > #define GENMASK_TYPE(t, h, l) \ > ((t)(GENMASK_INPUT_CHECK(h, l) + \ > (type_max(t) << (l) & \ > type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h))))) > > and works with all the GENMASK variants, including the U128 one! The > unit tests under lib/test_bits.c are all green. > > Of course, this does *not* work in assembly. But as explained before, > GENMASK_TYPE() is guarded by a #if !defined(__ASSEMBLY__), so all good! > > The question raised by Yury on whether or not we should keep > __GENMASK_U128() in the uapi still remains. And in full honesty, I will > not touch that one. This is not in the scope of this series. I vote for not touching it right now independently on its destiny. -- With Best Regards, Andy Shevchenko
