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Date: Wed, 25 Sep 2024 08:23:07 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Morten =?UTF-8?B?QnLDuHJ1cA==?= <mb@smartsharesystems.com>
Cc: "Robin Jarry" <rjarry@redhat.com>, <dev@dpdk.org>
Subject: Re: [PATCH dpdk] mbuf: fix strict aliasing error in allocator
Message-ID: <20240925082307.7162e556@fedora>
In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F72F@smartserver.smartshare.dk>
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On Wed, 25 Sep 2024 17:21:12 +0200
Morten Br=C3=B8rup <mb@smartsharesystems.com> wrote:
> From: Morten Br=C3=B8rup <mb@smartsharesystems.com>
> To: "Robin Jarry" <rjarry@redhat.com>, <dev@dpdk.org>
> Subject: RE: [PATCH dpdk] mbuf: fix strict aliasing error in allocator
> Date: Wed, 25 Sep 2024 17:21:12 +0200
>=20
> > From: Robin Jarry [mailto:rjarry@redhat.com]
> > Sent: Wednesday, 25 September 2024 10.00
> >=20
> > When building an application with -fstrict-aliasing -Wstrict-
> > aliasing=3D2,
> > we get errors triggered by rte_mbuf_raw_alloc() which is called inline
> > from rte_pktmbuf_alloc().
> >=20
> > ../dpdk/lib/mbuf/rte_mbuf.h: In function =E2=80=98rte_mbuf_raw_alloc=
=E2=80=99:
> > ../dpdk/lib/mbuf/rte_mbuf.h:600:42: error: dereferencing type-punned
> > pointer might break strict-aliasing rules [-Werror=3Dstrict-aliasing]
> > 600 | if (rte_mempool_get(mp, (void **)&m) < 0)
> > | ^~
> >=20
> > Avoid incorrect casting by changing the type of the returned variable.
> >=20
> > Signed-off-by: Robin Jarry <rjarry@redhat.com>
> > ---
> > lib/mbuf/rte_mbuf.h | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >=20
> > 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;
> >=20
> > - 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; =20
>=20
> Suggest:
> __rte_mbuf_raw_sanity_check((struct rte_mbuf *)m);
> return (struct rte_mbuf *)m;
Another way to avoid the warning would be to use a union?