[dpdk-dev] [PATCH] examples/performance-thread: fix segfault with in gcc 5.x

[Tomasz Kulasek <tomaszx.kulasek@intel.com>]

It seems that with gcc >5.x and -O2/-O3 optimization breaks packet grouping
algorithm in l3fwd-thread application causing segfault.

When last packet pointer "lp" and "pnum->u64" buffer points the same
memory buffer, high optimization can cause unpredictable results. It seems
that assignment of precalculated group sizes may interfere with
initialization of new group size when lp points value inside current group
and didn't should be changed.

With gcc >5.x and optimization we cannot be sure which assignment will be
done first, so the group size can be counted incorrectly causing segfault.

This patch eliminates intersection of assignment of initial group size
(lp[0] = 1) and precalculated group sizes when gptbl[v].idx < 4.

Fixes: d48415e1fee3 ("examples/performance-thread: add l3fwd-thread app")

Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
---
 examples/performance-thread/l3fwd-thread/main.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/examples/performance-thread/l3fwd-thread/main.c b/examples/performance-thread/l3fwd-thread/main.c
index 15c0a4d..3417fd5 100644
--- a/examples/performance-thread/l3fwd-thread/main.c
+++ b/examples/performance-thread/l3fwd-thread/main.c
@@ -1658,9 +1658,9 @@ port_groupx4(uint16_t pn[FWDSTEP + 1], uint16_t *lp, __m128i dp1, __m128i dp2)
 
 	/* if dest port value has changed. */
 	if (v != GRPMSK) {
-		lp = pnum->u16 + gptbl[v].idx;
-		lp[0] = 1;
 		pnum->u64 = gptbl[v].pnum;
+		pnum->u16[FWDSTEP] = 1;
+		lp = pnum->u16 + gptbl[v].idx;
 	}
 
 	return lp;
-- 
1.7.9.5