Hi, Tiezhu, On Tue, Dec 31, 2024 at 3:28 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote: > > There are objtool warnings compiled with the latest mainline LLVM: > > dc_fixpt_recip() falls through to next function dc_fixpt_sinc() > spl_fixpt_recip() falls through to next function spl_fixpt_sinc() > > Here are the call paths: > > dc_fixpt_recip() > dc_fixpt_from_fraction() > complete_integer_division_u64() > div64_u64_rem() > > spl_fixpt_recip() > spl_fixpt_from_fraction() > spl_complete_integer_division_u64() > spl_div64_u64_rem() > > This was introduced by a change in Clang from a few months: > > [SimplifyCFG] Deduce paths unreachable if they cause div/rem UB) > https://github.com/llvm/llvm-project/commit/37932643abab > > Since the ASSERT does not do anything to prevent the divide by zero > (just flags it with WARN_ON) and the rest of the code doesn't either, > the callers of division functions should harden them against dividing > by zero to avoid undefined behavior. > > Keep the current ASSERT for the aim of debugging, just add BUG() to > stop control flow if the divisior is zero. > > Suggested-by: Nathan Chancellor <nathan@xxxxxxxxxx> > Suggested-by: Xi Ruoyao <xry111@xxxxxxxxxxx> > Suggested-by: Rui Wang <wangrui@xxxxxxxxxxx> > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> > Link: https://lore.kernel.org/lkml/20241220223403.GA2605890@ax162/ > --- > drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c | 1 + > drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c b/drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c > index 88d3f9d7dd55..e15391e36b40 100644 > --- a/drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c > +++ b/drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c > @@ -52,6 +52,7 @@ static inline unsigned long long complete_integer_division_u64( > unsigned long long result; > > ASSERT(divisor); > + BUG_ON(!divisor); ASSERT() calls WARN(), so the warning message will print twice, but I don't have a better suggestion. :) Huacai > > result = div64_u64_rem(dividend, divisor, remainder); > > diff --git a/drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c b/drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c > index 131f1e3949d3..ce2036950808 100644 > --- a/drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c > +++ b/drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c > @@ -30,6 +30,7 @@ static inline unsigned long long spl_complete_integer_division_u64( > unsigned long long result; > > SPL_ASSERT(divisor); > + BUG_ON(!divisor); > > result = spl_div64_u64_rem(dividend, divisor, remainder); > > -- > 2.42.0 > >
