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?