Re: [ovs-dev] [PATCH 2/2] netdev-offload-dpdk: Fix vxlan vni cast-align warnings

[Eli Britstein via dev]

On 7/22/2021 3:28 PM, Ilya Maximets wrote:
External email: Use caution opening links or attachments

On 7/11/21 7:15 AM, Eli Britstein wrote:
Compiling with -Werror and -Wcast-align has errors like:

lib/netdev-offload-dpdk.c: In function 'dump_flow_pattern':
lib/netdev-offload-dpdk.c:385:38: error: cast increases required alignment
     of target type [-Werror=cast-align]
   385 |    ntohl(*(ovs_be32 *) vxlan_spec->vni) >> 8,
       |           ^

Fix them.

Reported-by: Harry Van Haaren <harry.van.haa...@intel.com>
Fixes: 4e432d6f8128 ("netdev-offload-dpdk: Support tnl/push using vxlan encap 
attribute.")
Fixes: e098c2f966cb ("netdev-dpdk-offload: Add vxlan pattern matching 
function.")
Signed-off-by: Eli Britstein <el...@nvidia.com>
---
  lib/netdev-offload-dpdk.c | 18 +++++++++++++-----
  1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/lib/netdev-offload-dpdk.c b/lib/netdev-offload-dpdk.c
index a24f92782..e4b19ae40 100644
--- a/lib/netdev-offload-dpdk.c
+++ b/lib/netdev-offload-dpdk.c
@@ -375,6 +375,8 @@ dump_flow_pattern(struct ds *s,
      } else if (item->type == RTE_FLOW_ITEM_TYPE_VXLAN) {
          const struct rte_flow_item_vxlan *vxlan_spec = item->spec;
          const struct rte_flow_item_vxlan *vxlan_mask = item->mask;
+        BUILD_ASSERT_DECL(offsetof(struct rte_flow_item_vxlan, vni) %
+                          sizeof(ovs_be32) == 0);

          ds_put_cstr(s, "vxlan ");
          if (vxlan_spec) {
@@ -382,8 +384,10 @@ dump_flow_pattern(struct ds *s,
                  vxlan_mask = &rte_flow_item_vxlan_mask;
              }
              DUMP_PATTERN_ITEM(vxlan_mask->vni, "vni", "%"PRIu32,
-                              ntohl(*(ovs_be32 *) vxlan_spec->vni) >> 8,
-                              ntohl(*(ovs_be32 *) vxlan_mask->vni) >> 8);
+                              ntohl(*ALIGNED_CAST(ovs_be32 *,
+                                                  vxlan_spec->vni)) >> 8,
+                              ntohl(*ALIGNED_CAST(ovs_be32 *,
+                                                  vxlan_mask->vni)) >> 8);
          }
          ds_put_cstr(s, "/ ");
      } else {
@@ -417,8 +421,10 @@ dump_vxlan_encap(struct ds *s, const struct rte_flow_item 
*items)
      ds_put_format(s, "set vxlan ip-version %s ",
                    ipv4 ? "ipv4" : ipv6 ? "ipv6" : "ERR");
      if (vxlan) {
+        BUILD_ASSERT_DECL(offsetof(struct rte_flow_item_vxlan, vni) %
+                          sizeof(ovs_be32) == 0);
          ds_put_format(s, "vni %"PRIu32" ",
-                      ntohl(*(ovs_be32 *) vxlan->vni) >> 8);
+                      ntohl(*ALIGNED_CAST(ovs_be32 *, vxlan->vni)) >> 8);
      }
      if (udp) {
          ds_put_format(s, "udp-src %"PRIu16" udp-dst %"PRIu16" ",
@@ -1003,9 +1009,11 @@ parse_vxlan_match(struct flow_patterns *patterns,
      vx_spec = xzalloc(sizeof *vx_spec);
      vx_mask = xzalloc(sizeof *vx_mask);

-    put_unaligned_be32((ovs_be32 *) vx_spec->vni,
+    BUILD_ASSERT_DECL(offsetof(struct rte_flow_item_vxlan, vni) %
+                      sizeof(ovs_be32) == 0);
+    put_unaligned_be32(ALIGNED_CAST(ovs_be32 *, vx_spec->vni),
                         htonl(ntohll(match->flow.tunnel.tun_id) << 8));
-    put_unaligned_be32((ovs_be32 *) vx_mask->vni,
+    put_unaligned_be32(ALIGNED_CAST(ovs_be32 *, vx_mask->vni),
                         htonl(ntohll(match->wc.masks.tunnel.tun_id) << 8));

      consumed_masks->tunnel.tun_id = 0;

Same concerns here about the build time assertion as in the patch #1.
It also seems redundant to use put_unaligned_* functions and have a
build assertion at the same time.

Suggesting to just use put/get_unaligned_* in all cases and remove
build time assertions.

The code before this patch just uses (for example) put_unaligned_be32, 
which its 1st argument is (ovs_be32 *).

vni in struct rte_flow_item_vxlan  in dpdk is uint8_t vni[3]; /**< VXLAN 
identifier. */

I use ALIGNED_CAST to mute the warning, and the assert to make sure the 
alignment is correct.

I don't understand your suggestion here, unless you suggest to use 
memcpy as suggested in patch#1.


Best regards, Ilya Maximets.
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