Re: [dpdk-dev] [PATCH V2 1/3] net: avoid cast-align warning in VLAN insert function

On 10/21/2021 6:48 PM, Stephen Hemminger wrote:

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On Thu, 21 Oct 2021 11:51:30 +0300
Eli Britstein [off-list ref] wrote:

quoted

In rte_vlan_insert there is a casting of rte_pktmbuf_prepend returned
value to (struct rte_ether_hdr *), which causes cast-align warning when
using strict cast align flag with supporting gcc:
gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
CFLAGS="-Wcast-align=strict" make V=1 -C examples/l2fwd clean static

In file included from main.c:35:
/dpdk/build/include/rte_ether.h:370:7: warning: cast increases required
alignment of target type [-Wcast-align]
   370 |  nh = (struct rte_ether_hdr *)
       |       ^

As the code assumes correct alignment, add first a (void *) casting, to
avoid the warning.

Fixes: c974021a5949 ("ether: add soft vlan encap/decap")
Cc: stable@dpdk.org

Signed-off-by: Eli Britstein <redacted>
Acked-by: Olivier Matz <redacted>

After cast to void * the second cast is not necessary.

         nh = (void *)rte_pktmbuf_prepend(...)

Ideally rte_pktmbuf_prepend() should return void * but that is
an API change.

Removing the second cast, it is silently done anyway, as 'nh' is of type 'struct rte_ether_hdr *'.

Going with this approach (I can also do it for patch 3/3), we can change rte_pktmbuf_prepend to return (void *), and let the applications using it do the silent cast.

What do you think?