[PATCH dpdk v2] mbuf: fix strict aliasing error in allocator

[Ali Alnubani]

> -----Original Message-----
> From: Robin Jarry <rjarry at redhat.com>
> Sent: Wednesday, September 25, 2024 6:41 PM
> To: dev at dpdk.org
> Subject: [PATCH dpdk v2] mbuf: fix strict aliasing error in allocator
> 
> 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 using an inline union variable.
> 
> Signed-off-by: Robin Jarry <rjarry at redhat.com>
> ---
> 
> Notes:
>     v2: use inline union to fix -Wincompatible-pointer-types
> 
>  lib/mbuf/rte_mbuf.h | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
> index babe16c72ccb..0d2e0e64b3ce 100644
> --- a/lib/mbuf/rte_mbuf.h
> +++ b/lib/mbuf/rte_mbuf.h
> @@ -595,12 +595,15 @@ __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;
> +	union {
> +		void *ptr;
> +		struct rte_mbuf *m;
> +	} ret;
> 
> -	if (rte_mempool_get(mp, (void **)&m) < 0)
> +	if (rte_mempool_get(mp, &ret.ptr) < 0)
>  		return NULL;
> -	__rte_mbuf_raw_sanity_check(m);
> -	return m;
> +	__rte_mbuf_raw_sanity_check(ret.m);
> +	return ret.m;
>  }
> 
>  /**
> --
> 2.46.1

Hello,

We noticed the failure in ci/iol-mellanox-Performance and ran a few performance test cases on NVIDIA hardware and found no regressions.
Additionally ran build and functional test cases that also passed.

Tested-by: Ali Alnubani <alialnu at nvidia.com>

Regards,
Ali