[dpdk-dev] [PATCH] net/virtio: fix gcc6 i686 compiler error

[Ferruh Yigit <ferruh.yigit@intel.com>]

This is for target i686-native-linuxapp-gcc and gcc6,

Compilation error is:
== Build drivers/net/virtio
  CC virtio_rxtx_simple.o
In file included from
.../build/include/rte_mempool.h:77:0,
                 from
.../drivers/net/virtio/virtio_rxtx_simple.c:46:
.../drivers/net/virtio/virtio_rxtx_simple.c: In
function ‘virtio_xmit_pkts_simple’:
.../build/include/rte_memcpy.h:551:2: error: array
subscript is above array bounds [-Werror=array-bounds]
  rte_mov16((uint8_t *)dst + 1 * 16, (const uint8_t *)src + 1 * 16);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Call stack is as following:

virtio_xmit_pkts_simple
  virtio_xmit_cleanup
    rte_mempool_put_bulk
      rte_mempool_generic_put
        __mempool_generic_put
	  rte_memcpy

The array used as source buffer in virtio_xmit_cleanup (free) is a
pointer array with 32 elements, in 32bit this makes 128 bytes.

in rte_memcpy() implementation, there a code piece as following:
if (size > 256) {
    rte_move128(...);
    rte_move128(...); <--- [1]
    ....
}

The compiler traces the array all through the call stack and knows the
size of array is 128 and generates a warning on above [1] which tries to
access beyond byte 128.
But unfortunately it ignores the "(size > 256)" check.

Giving a hint to compiler that variable "size" is related to the size of
the source buffer fixes compiler warning.

Fixes: 863bfb474493 ("mempool: optimize copy in cache")

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
---
 drivers/net/virtio/virtio_rxtx_simple.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio/virtio_rxtx_simple.c b/drivers/net/virtio/virtio_rxtx_simple.c
index 242ad90..d8fcc15 100644
--- a/drivers/net/virtio/virtio_rxtx_simple.c
+++ b/drivers/net/virtio/virtio_rxtx_simple.c
@@ -301,7 +301,7 @@ static inline void
 virtio_xmit_cleanup(struct virtqueue *vq)
 {
 	uint16_t i, desc_idx;
-	int nb_free = 0;
+	uint32_t nb_free = 0;
 	struct rte_mbuf *m, *free[VIRTIO_TX_MAX_FREE_BUF_SZ];
 
 	desc_idx = (uint16_t)(vq->vq_used_cons_idx &
@@ -319,13 +319,16 @@ virtio_xmit_cleanup(struct virtqueue *vq)
 					free[nb_free++] = m;
 				else {
 					rte_mempool_put_bulk(free[0]->pool,
-						(void **)free, nb_free);
+						(void **)free,
+						RTE_MIN(RTE_DIM(free),
+							nb_free));
 					free[0] = m;
 					nb_free = 1;
 				}
 			}
 		}
-		rte_mempool_put_bulk(free[0]->pool, (void **)free, nb_free);
+		rte_mempool_put_bulk(free[0]->pool, (void **)free,
+			RTE_MIN(RTE_DIM(free), nb_free));
 	} else {
 		for (i = 1; i < VIRTIO_TX_FREE_NR; i++) {
 			m = (struct rte_mbuf *)vq->vq_descx[desc_idx++].cookie;
-- 
2.7.4