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Date: Fri, 7 Jun 2019 11:35:12 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>, "Richardson, Bruce"
<bruce.richardson@intel.com>, Andrew Rybchenko <arybchenko@solarflare.com>
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Subject: Re: [dpdk-dev] [PATCH v4 5/8] net/ether: mark ethernet addresses as
being 2-byte aligned
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On Fri, 7 Jun 2019 16:59:32 +0000
"Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:
> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen Hemminger
> > Sent: Wednesday, June 5, 2019 7:10 PM
> > To: dev@dpdk.org
> > Cc: Richardson, Bruce <bruce.richardson@intel.com>; Stephen Hemminger <=
stephen@networkplumber.org>; Andrew Rybchenko
> > <arybchenko@solarflare.com>
> > Subject: [dpdk-dev] [PATCH v4 5/8] net/ether: mark ethernet addresses a=
s being 2-byte aligned
> >=20
> > From: Bruce Richardson <bruce.richardson@intel.com>
> >=20
> > When including the rte_ether.h header in applications with warnings
> > enabled, a warning was given because of the assumption of 2-byte alignm=
ent
> > of ethernet addresses when processing them.
> >=20
> > .../include/rte_ether.h:149:2: warning: converting a packed =E2=80=98co=
nst
> > struct ether_addr=E2=80=99 pointer (alignment 1) to a =E2=80=98unalig=
ned_uint16_t=E2=80=99
> > {aka =E2=80=98const short unsigned int=E2=80=99} pointer (alignment 2=
) may result in
> > an unaligned pointer value [-Waddress-of-packed-member]
> > 149 | const unaligned_uint16_t *ea_words =3D (const unaligned_uint16_t=
*)ea;
> > | ^~~~~
> >=20
> > Since ethernet addresses should always be aligned on a two-byte boundar=
y,
> > we can just inform the compiler of this assumption to remove the warnin=
gs
> > and allow us to always access the addresses using 16-bit operations.
> >=20
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>
> > ---
> > lib/librte_net/rte_ether.h | 11 ++++++-----
> > 1 file changed, 6 insertions(+), 5 deletions(-)
> >=20
> > diff --git a/lib/librte_net/rte_ether.h b/lib/librte_net/rte_ether.h
> > index feb35a33c94b..d7b76ddf63eb 100644
> > --- a/lib/librte_net/rte_ether.h
> > +++ b/lib/librte_net/rte_ether.h
> > @@ -58,7 +58,8 @@ extern "C" {
> > * See http://standards.ieee.org/regauth/groupmac/tutorial.html
> > */
> > struct rte_ether_addr {
> > - uint8_t addr_bytes[RTE_ETHER_ADDR_LEN]; /**< Addr bytes in tx order */
> > + uint8_t addr_bytes[RTE_ETHER_ADDR_LEN] __rte_aligned(2);
> > + /**< Addr bytes in tx order */
> > } __attribute__((__packed__)); =20
>=20
> Hmm, that would change layout of any struct/union that has struct rte_eth=
er_addr inside.
> So seems like implicit ABI breakage to me.
> Konstantin
There was no rte_ether_addr in previous releases.