Messages in this thread | | | From | Arnd Bergmann <> | Date | Sat, 2 Jan 2021 12:23:20 +0100 | Subject | Re: [PATCH] i915: fix shift warning |
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On Wed, Dec 30, 2020 at 4:56 PM Chris Wilson <chris@chris-wilson.co.uk> wrote: > > Quoting Arnd Bergmann (2020-12-30 15:39:14) > > From: Arnd Bergmann <arnd@arndb.de> > > > > Randconfig builds on 32-bit machines show lots of warnings for > > the i915 driver for incorrect bit masks like: > > mask is a u8. > > VCS0 is 2, I915_MAX_VCS 4 > > (u8 & GENMASK(5, 2)) >> 2
Ah right, I misread the warning then.
> > drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:2584:9: error: shift count >= width of type [-Werror,-Wshift-count-overflow] > > return hweight64(VDBOX_MASK(&i915->gt)); > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > include/asm-generic/bitops/const_hweight.h:29:49: note: expanded from macro 'hweight64' > > #define hweight64(w) (__builtin_constant_p(w) ? __const_hweight64(w) : __arch_hweight64(w)) > > So it's upset by hweight64() on the unsigned long?
I suspect what is going on is that clang once again warns because it performs more code checks before dead-code elimination than gcc does. The warning is for the __const_hweight64() case, which is not actually used here because the input is not a compile-time constant.
> So hweight_long?
That seems to work, I'll send a new version with that.
> Or use a cast, hweight8((intel_engine_mask_t)VDMASK())? > > static __always_inline int engine_count(intel_engine_mask_t mask) > { > return sizeof(mask) == 1 ? hweight8(mask) : > sizeof(mask) == 2 ? hweight16(mask) : > sizeof(mask) == 4 ? hweight32(mask) : > hweight64(mask); > }
Fine with me as well. If you prefer that way, I'll let you handle that.
Arnd
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