[dpdk-dev] [PATCH v4 5/8] net/ether: mark ethernet addresses as being 2-byte aligned

[Stephen Hemminger]

On Fri, 7 Jun 2019 16:59:32 +0000
"Ananyev, Konstantin" <konstantin.ananyev at intel.com> wrote:

> > -----Original Message-----
> > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Stephen Hemminger
> > Sent: Wednesday, June 5, 2019 7:10 PM
> > To: dev at dpdk.org
> > Cc: Richardson, Bruce <bruce.richardson at intel.com>; Stephen Hemminger <stephen at networkplumber.org>; Andrew Rybchenko
> > <arybchenko at solarflare.com>
> > Subject: [dpdk-dev] [PATCH v4 5/8] net/ether: mark ethernet addresses as being 2-byte aligned
> > 
> > From: Bruce Richardson <bruce.richardson at intel.com>
> > 
> > When including the rte_ether.h header in applications with warnings
> > enabled, a warning was given because of the assumption of 2-byte alignment
> > of ethernet addresses when processing them.
> > 
> > .../include/rte_ether.h:149:2: warning: converting a packed ‘const
> >   struct ether_addr’ pointer (alignment 1) to a ‘unaligned_uint16_t’
> >   {aka ‘const short unsigned int’} pointer (alignment 2) may result in
> >   an unaligned pointer value [-Waddress-of-packed-member]
> > 149 |  const unaligned_uint16_t *ea_words = (const unaligned_uint16_t *)ea;
> >     |  ^~~~~
> > 
> > Since ethernet addresses should always be aligned on a two-byte boundary,
> > we can just inform the compiler of this assumption to remove the warnings
> > and allow us to always access the addresses using 16-bit operations.
> > 
> > Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> > Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
> > Reviewed-by: Andrew Rybchenko <arybchenko at solarflare.com>
> > ---
> >  lib/librte_net/rte_ether.h | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > 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__));  
> 
> Hmm, that would change layout of any struct/union that has struct rte_ether_addr inside.
> So seems like implicit ABI breakage to me.
> Konstantin

There was no rte_ether_addr in previous releases.