On 2020-02-12 6:07 p.m., Nathan Chancellor wrote: > On Wed, Feb 12, 2020 at 09:52:52AM +0100, Michel Dänzer wrote: >> On 2020-02-11 9:39 p.m., Nathan Chancellor wrote: >>> On Tue, Feb 11, 2020 at 10:41:48AM +0100, Michel Dänzer wrote: >>>> On 2020-02-11 7:13 a.m., Nathan Chancellor wrote: >>>>> A recent commit in clang added -Wtautological-compare to -Wall, which is >>>>> enabled for i915 so we see the following warning: >>>>> >>>>> ../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1485:22: warning: >>>>> result of comparison of constant 576460752303423487 with expression of >>>>> type 'unsigned int' is always false >>>>> [-Wtautological-constant-out-of-range-compare] >>>>> if (unlikely(remain > N_RELOC(ULONG_MAX))) >>>>> ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ >>>>> >>>>> This warning only happens on x86_64 but that check is relevant for >>>>> 32-bit x86 so we cannot remove it. >>>> >>>> That's suprising. AFAICT N_RELOC(ULONG_MAX) works out to the same value >>>> in both cases, and remain is a 32-bit value in both cases. How can it be >>>> larger than N_RELOC(ULONG_MAX) on 32-bit (but not on 64-bit)? >>>> >>> >>> Hi Michel, >>> >>> Can't this condition be true when UINT_MAX == ULONG_MAX? >> >> Oh, right, I think I was wrongly thinking long had 64 bits even on 32-bit. >> >> >> Anyway, this suggests a possible better solution: >> >> #if UINT_MAX == ULONG_MAX >> if (unlikely(remain > N_RELOC(ULONG_MAX))) >> return -EINVAL; >> #endif >> >> >> Or if that can't be used for some reason, something like >> >> if (unlikely((unsigned long)remain > N_RELOC(ULONG_MAX))) >> return -EINVAL; >> >> should silence the warning. > > I do like this one better than the former. FWIW, one downside of this one compared to all alternatives (presumably) is that it might end up generating actual code even on 64-bit, which always ends up skipping the return. -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and X developer _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
