[PATCH dpdk] mbuf: fix strict aliasing error in allocator

[Morten Brørup]

> From: Robin Jarry [mailto:rjarry at redhat.com]
> Sent: Wednesday, 25 September 2024 10.00
> 
> When building an application with -fstrict-aliasing -Wstrict-
> aliasing=2,
> we get errors triggered by rte_mbuf_raw_alloc() which is called inline
> from rte_pktmbuf_alloc().
> 
>  ../dpdk/lib/mbuf/rte_mbuf.h: In function ‘rte_mbuf_raw_alloc’:
>  ../dpdk/lib/mbuf/rte_mbuf.h:600:42: error: dereferencing type-punned
>  pointer might break strict-aliasing rules [-Werror=strict-aliasing]
>    600 |         if (rte_mempool_get(mp, (void **)&m) < 0)
>        |                                          ^~
> 
> Avoid incorrect casting by changing the type of the returned variable.
> 
> Signed-off-by: Robin Jarry <rjarry at redhat.com>
> ---
>  lib/mbuf/rte_mbuf.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
> index babe16c72ccb..bab1fb94d41d 100644
> --- a/lib/mbuf/rte_mbuf.h
> +++ b/lib/mbuf/rte_mbuf.h
> @@ -595,9 +595,9 @@ __rte_mbuf_raw_sanity_check(__rte_unused const
> struct rte_mbuf *m)
>   */
>  static inline struct rte_mbuf *rte_mbuf_raw_alloc(struct rte_mempool
> *mp)
>  {
> -	struct rte_mbuf *m;
> +	void *m;
> 
> -	if (rte_mempool_get(mp, (void **)&m) < 0)
> +	if (rte_mempool_get(mp, &m) < 0)
>  		return NULL;
>  	__rte_mbuf_raw_sanity_check(m);
>  	return m;

Suggest:
	__rte_mbuf_raw_sanity_check((struct rte_mbuf *)m);
	return (struct rte_mbuf *)m;

> --
> 2.46.1

Please confirm that this builds with RTE_LIBRTE_MBUF_DEBUG and RTE_ENABLE_ASSERT set in config/rte_config.h. When confirmed, you may add:
Acked-by: Morten Brørup <mb at smartsharesystems.com>