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]>
Acked-by: Marat Khalili <[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
