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

[Ananyev, Konstantin]

> > >
> > > 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.

I suppose you refer to the fact that struct ether_addr was renamed to rte_ether_addr by:
https://git.dpdk.org/dpdk/commit/?id=6d13ea8e8e49ab957deae2bba5ecf4a4bfe747d1 
As I understand, Olivier patches in that rework introduce API change only,  keeping ABI unchanged.
While your patch makes ABI breakage possible.
Konstantin