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. Yours sincerely, Vincent Mailhol
