[dpdk-dev] [PATCH] net: fix the way how L4 checksum choice is tested

[Ivan Malov]

The API to prepare checksum offloads mistreats L4
checksum type enum values as self-contained flags.

Turning these flag checks into enum checks causes
warnings by GCC about possibly uninitialised IPv4
header pointer. The issue was found to show up in
the case of GCC versions 4.8.5 and 5.4.0, however,
it might be the case for a wider variety of other
versions. As GCC version 7.4.0 is not susceptible
to the said false positive assessment, this patch
maintains a compiler barrier for earlier versions.

Fixes: 4fb7e803eb1a ("ethdev: add Tx preparation")
Cc: Tomasz Kulasek <tomaszx.kulasek at intel.com>
Cc: stable at dpdk.org

Signed-off-by: Ivan Malov <ivan.malov at oktetlabs.ru>
---
 lib/librte_net/rte_net.h | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/lib/librte_net/rte_net.h b/lib/librte_net/rte_net.h
index 7088584..fb09431 100644
--- a/lib/librte_net/rte_net.h
+++ b/lib/librte_net/rte_net.h
@@ -151,7 +151,19 @@ uint32_t rte_net_get_ptype(const struct rte_mbuf *m,
 			ipv4_hdr->hdr_checksum = 0;
 	}
 
-	if ((ol_flags & PKT_TX_UDP_CKSUM) == PKT_TX_UDP_CKSUM) {
+#ifdef GCC_VERSION
+#if GCC_VERSION < 70400
+	/*
+	 * Earlier versions of GCC suspect access to possibly
+	 * uninitialised ipv4_hdr in the code below, although
+	 * the said variable is properly initialised above.
+	 * Use compiler barrier to cope with the problem.
+	 */
+	rte_compiler_barrier();
+#endif
+#endif
+
+	if ((ol_flags & PKT_TX_L4_MASK) == PKT_TX_UDP_CKSUM) {
 		if (ol_flags & PKT_TX_IPV4) {
 			udp_hdr = (struct rte_udp_hdr *)((char *)ipv4_hdr +
 					m->l3_len);
@@ -167,7 +179,7 @@ uint32_t rte_net_get_ptype(const struct rte_mbuf *m,
 			udp_hdr->dgram_cksum = rte_ipv6_phdr_cksum(ipv6_hdr,
 					ol_flags);
 		}
-	} else if ((ol_flags & PKT_TX_TCP_CKSUM) ||
+	} else if ((ol_flags & PKT_TX_L4_MASK) == PKT_TX_TCP_CKSUM ||
 			(ol_flags & PKT_TX_TCP_SEG)) {
 		if (ol_flags & PKT_TX_IPV4) {
 			/* non-TSO tcp or TSO */
-- 
1.8.3.1