Hi Bruce,
On Thu, May 16, 2019 at 04:54:57PM +0100, Bruce Richardson wrote:
> 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,
I'm a bit reserved about this last assumption. The ethernet address
structure may be used in a private structure, whose alignment is 1. Are
we sure that there is no (funny) protocol that carries unaligned
ethernet addresses?
Shouldn't we change the definition of unaligned_uint16_t instead?
Or change the rte_is_broadcast_ether_addr() function?
> 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.richard...@intel.com>
>
> ---
>
> Although this is an ABI break, the network structures are all being renamed
> in this release, and a deprecation notice was previously posted for it.
Yes, but the network renaming is identified in the release note as an
API break, not an ABI break.
> ---
> lib/librte_net/rte_ether.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/librte_net/rte_ether.h b/lib/librte_net/rte_ether.h
> index 3a87ff184..8090b7c01 100644
> --- a/lib/librte_net/rte_ether.h
> +++ b/lib/librte_net/rte_ether.h
> @@ -55,7 +55,8 @@ extern "C" {
> * See http://standards.ieee.org/regauth/groupmac/tutorial.html
> */
> struct ether_addr {
> - uint8_t addr_bytes[ETHER_ADDR_LEN]; /**< Addr bytes in tx order */
> + /** Addr bytes in tx order */
> + uint8_t addr_bytes[ETHER_ADDR_LEN] __rte_aligned(2);
> } __attribute__((__packed__));
>
> #define ETHER_LOCAL_ADMIN_ADDR 0x02 /**< Locally assigned Eth. address. */
> --
> 2.21.0
>
