[PATCH v5] ethdev: fix strict aliasing lead to link cannot be up

[Chengwen Feng <fengchengwen@huawei.com>]

Fix a problem introduced by a compiler upgrade (from gcc10 to gcc12.3),
which will lead the hns3 NIC can't link up. The root cause is strict
aliasing violation in rte_eth_linkstatus_set() with hns3 driver, see
[1] for more details.

This commit use union to avoid such aliasing violation.

Note: DPDK CI report compiler error (see [2] for more details):
../drivers/net/cxgbe/cxgbe_ethdev.c:214:9: error: missing braces around
initializer [-Werror=missing-braces]
  struct rte_eth_link new_link = { 0 };
So this commit replace { 0 } with memset in cxgbe.

[1] Strict aliasing problem with rte_eth_linkstatus_set()
    https://marc.info/?l=dpdk-dev&m=171274148514777&w=3
[2] https://mails.dpdk.org/archives/test-report/2024-April/637966.html

Cc: stable@dpdk.org

Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
Signed-off-by: Dengdui Huang <huangdengdui@huawei.com>

---
v5: fix DPDK CI compiler error due to GCC extension [-Werror=pedantic]
v4: fix DPDK CI compiler error with cxgbe.
v3: fix checkpatch warning "missing --in-reply-to".
v2: add RTE_ATOMIC(uint64_t) wrap which address Morten's comment.

---
 drivers/net/cxgbe/cxgbe_ethdev.c |  3 ++-
 lib/ethdev/ethdev_driver.h       | 23 +++++++----------------
 lib/ethdev/rte_ethdev.h          | 17 +++++++++++------
 3 files changed, 20 insertions(+), 23 deletions(-)

diff --git a/drivers/net/cxgbe/cxgbe_ethdev.c b/drivers/net/cxgbe/cxgbe_ethdev.c
index a27b9b266e..9b6a3651f9 100644
--- a/drivers/net/cxgbe/cxgbe_ethdev.c
+++ b/drivers/net/cxgbe/cxgbe_ethdev.c
@@ -211,9 +211,9 @@ int cxgbe_dev_link_update(struct rte_eth_dev *eth_dev,
 	unsigned int i, work_done, budget = 32;
 	struct link_config *lc = &pi->link_cfg;
 	struct adapter *adapter = pi->adapter;
-	struct rte_eth_link new_link = { 0 };
 	u8 old_link = pi->link_cfg.link_ok;
 	struct sge *s = &adapter->sge;
+	struct rte_eth_link new_link;
 
 	for (i = 0; i < CXGBE_LINK_STATUS_POLL_CNT; i++) {
 		if (!s->fw_evtq.desc)
@@ -232,6 +232,7 @@ int cxgbe_dev_link_update(struct rte_eth_dev *eth_dev,
 		rte_delay_ms(CXGBE_LINK_STATUS_POLL_MS);
 	}
 
+	memset(&new_link, 0, sizeof(new_link));
 	new_link.link_status = cxgbe_force_linkup(adapter) ?
 			       RTE_ETH_LINK_UP : pi->link_cfg.link_ok;
 	new_link.link_autoneg = (lc->link_caps & FW_PORT_CAP32_ANEG) ? 1 : 0;
diff --git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h
index 0dbf2dd6a2..9d831d5c84 100644
--- a/lib/ethdev/ethdev_driver.h
+++ b/lib/ethdev/ethdev_driver.h
@@ -1674,18 +1674,13 @@ static inline int
 rte_eth_linkstatus_set(struct rte_eth_dev *dev,
 		       const struct rte_eth_link *new_link)
 {
-	RTE_ATOMIC(uint64_t) *dev_link = (uint64_t __rte_atomic *)&(dev->data->dev_link);
-	union {
-		uint64_t val64;
-		struct rte_eth_link link;
-	} orig;
-
-	RTE_BUILD_BUG_ON(sizeof(*new_link) != sizeof(uint64_t));
+	struct rte_eth_link old_link;
 
-	orig.val64 = rte_atomic_exchange_explicit(dev_link, *(const uint64_t *)new_link,
-					rte_memory_order_seq_cst);
+	old_link.val64 = rte_atomic_exchange_explicit(&dev->data->dev_link.val64,
+						      new_link->val64,
+						      rte_memory_order_seq_cst);
 
-	return (orig.link.link_status == new_link->link_status) ? -1 : 0;
+	return (old_link.link_status == new_link->link_status) ? -1 : 0;
 }
 
 /**
@@ -1701,12 +1696,8 @@ static inline void
 rte_eth_linkstatus_get(const struct rte_eth_dev *dev,
 		       struct rte_eth_link *link)
 {
-	RTE_ATOMIC(uint64_t) *src = (uint64_t __rte_atomic *)&(dev->data->dev_link);
-	uint64_t *dst = (uint64_t *)link;
-
-	RTE_BUILD_BUG_ON(sizeof(*link) != sizeof(uint64_t));
-
-	*dst = rte_atomic_load_explicit(src, rte_memory_order_seq_cst);
+	link->val64 = rte_atomic_load_explicit(&dev->data->dev_link.val64,
+					       rte_memory_order_seq_cst);
 }
 
 /**
diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
index 147257d6a2..548fada1c7 100644
--- a/lib/ethdev/rte_ethdev.h
+++ b/lib/ethdev/rte_ethdev.h
@@ -332,12 +332,17 @@ struct rte_eth_stats {
 /**
  * A structure used to retrieve link-level information of an Ethernet port.
  */
-__extension__
-struct __rte_aligned(8) rte_eth_link { /**< aligned for atomic64 read/write */
-	uint32_t link_speed;        /**< RTE_ETH_SPEED_NUM_ */
-	uint16_t link_duplex  : 1;  /**< RTE_ETH_LINK_[HALF/FULL]_DUPLEX */
-	uint16_t link_autoneg : 1;  /**< RTE_ETH_LINK_[AUTONEG/FIXED] */
-	uint16_t link_status  : 1;  /**< RTE_ETH_LINK_[DOWN/UP] */
+struct rte_eth_link {
+	union {
+		RTE_ATOMIC(uint64_t) val64; /**< used for atomic64 read/write */
+		__extension__
+		struct {
+			uint32_t link_speed;	    /**< RTE_ETH_SPEED_NUM_ */
+			uint16_t link_duplex  : 1;  /**< RTE_ETH_LINK_[HALF/FULL]_DUPLEX */
+			uint16_t link_autoneg : 1;  /**< RTE_ETH_LINK_[AUTONEG/FIXED] */
+			uint16_t link_status  : 1;  /**< RTE_ETH_LINK_[DOWN/UP] */
+		};
+	};
 };
 
 /**@{@name Link negotiation
-- 
2.17.1