[dpdk-dev] [PATCH] ether: mark ethernet addresses as being 2-byte aligned

Bruce Richardson bruce.richardson at intel.com
Thu May 16 17:54:57 CEST 2019

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>


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.
 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. */

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