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From: Olivier Matz <olivier.matz@6wind.com>
To: Bruce Richardson <bruce.richardson@intel.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>,
	DPDK Dev List <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] ether: mark ethernet addresses as being 2-byte aligned
Date: Mon, 1 Jul 2019 15:11:12 +0200	[thread overview]
Message-ID: <20190701131112.kdz3koexxyou466k@platinum> (raw)
In-Reply-To: <20190516155457.4006-1-bruce.richardson@intel.com>

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.richardson@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
> 

  parent reply	other threads:[~2019-07-01 13:11 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16 15:54 Bruce Richardson
2019-05-16 18:04 ` Kevin Traynor
2019-05-16 20:38   ` Bruce Richardson
2019-07-01 13:11 ` Olivier Matz [this message]
2019-07-01 13:38   ` Bruce Richardson
2019-07-01 14:14     ` Olivier Matz
2019-07-01 14:28       ` Bruce Richardson
     [not found] ` <1e5856a8-108b-1f0c-6ce7-b7c9eafac658@sitilge.id.lv>
2020-02-05 13:45   ` Bruce Richardson
2020-02-09 19:32     ` Martins Eglitis

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