On Fri, Sep 05, 2025 at 10:16:33AM +0200, Anders Roxell wrote: > > - v = FIELD_PREP(PCI_EXP_DEVCTL_READRQ, ffs(rq) - 8); > > + firstbit = ffs(rq); > > + if (firstbit < 8) > > + return -EINVAL; > > + v = FIELD_PREP(PCI_EXP_DEVCTL_READRQ, firstbit - 8); > > Hi Kees, > > Thank you for looking into this. > > These warnings are not a one time thing. the later versions of gcc > can figure it > out that firstbit is at least 8 based on the "rq < 128" (i guess), so > we're adding > bogus code. maybe we should just disable the check for gcc-8. I think the issue is that GCC thinks it knows the range for ffs is not the entire [0..UINT_MAX], but it _doesn't_ know how "rq" affects the outcome. (The range checker warnings kick in when it's not the whole range of a given type.) But I am just guessing, based on what how I've seen in behave in the past. > Maybe something like this: > > diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h > index 5355f8f806a9..4716025c98c7 100644 > --- a/include/linux/bitfield.h > +++ b/include/linux/bitfield.h > @@ -65,9 +65,20 @@ > BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \ > _pfx "mask is not constant"); \ > BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero"); \ > - BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \ > - ~((_mask) >> __bf_shf(_mask)) & \ > - (0 + (_val)) : 0, \ > + /* Value validation disabled for gcc < 9 due to > __attribute_const__ issues. > + */ \ > + BUILD_BUG_ON_MSG(__GNUC__ >= 9 && > __builtin_constant_p(_val) ? \ > + ~((_mask) >> __bf_shf(_mask)) & > \ > + (0 + (_val)) : 0, > \ > _pfx "value too large for the field"); \ > BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \ > __bf_cast_unsigned(_reg, ~0ull), \ > > I found similar patterns with ffs and FIELD_PREP here > drivers/dma/uniphier-xdmac.c row 156 and 165 > drivers/gpu/drm/i915/display/intel_cursor_regs.h row 17 You got warnings for these? -- Kees Cook
