> -----Original Message----- > From: Bruce Richardson <[email protected]> > Sent: Thursday 4 December 2025 18:21 > To: [email protected] > Cc: Bruce Richardson <[email protected]>; [email protected] > Subject: [PATCH v2 02/10] app/test: fix undefined behaviour in red autotest > > The shift of a negative number (or very large positive) is undefined > behaviour which causes errors when run with UBSan. Fix this by making > the behaviour explicit for the edge case of n being zero in the > calculation. > > Fixes: de3cfa2c9823 ("sched: initial import") > Cc: [email protected] > > Signed-off-by: Bruce Richardson <[email protected]> > --- > lib/sched/rte_red.h | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/lib/sched/rte_red.h b/lib/sched/rte_red.h > index e62abb9295..3b90cc46a9 100644 > --- a/lib/sched/rte_red.h > +++ b/lib/sched/rte_red.h > @@ -172,8 +172,15 @@ __rte_red_calc_qempty_factor(uint8_t wq_log2, uint16_t m) > f = (n >> 6) & 0xf; > n >>= 10; > > - if (n < RTE_RED_SCALING) > + if (n < RTE_RED_SCALING) { > + /* When n == 0, no rounding or shifting needed. > + * For n > 0, add 2^(n-1) for rounding before right shift. > + * This avoids UB from (1 << -1) when n == 0. > + */ > + if (n == 0) > + return (uint16_t) rte_red_pow2_frac_inv[f]; > return (uint16_t) ((rte_red_pow2_frac_inv[f] + (1 << (n - 1))) > >> n); > + } > > return 0; > } > -- > 2.51.0
Acked-by: Marat Khalili <[email protected]>
