[PATCH v12 3/3] eal/net: add workaround for GCC optimization bug

[scott.k.mitch1 at gmail.com]

From: Scott <scott_mitchell at apple.com>

GCC has a bug where it incorrectly elides struct initialization in
inline functions when strict aliasing is enabled (-O2/-O3/-Os), causing
reads from uninitialized memory. This affects both designated initializers
and manual field assignment.

Add RTE_FORCE_INIT_BARRIER macro that uses an asm volatile memory barrier
to prevent the compiler from incorrectly optimizing away struct
initialization. Apply the workaround to pseudo-header checksum functions
in rte_ip4.h, rte_ip6.h, hinic driver, and mlx5 driver.

Signed-off-by: Scott Mitchell <scott.k.mitch1 at gmail.com>
---
 drivers/net/hinic/hinic_pmd_tx.c |  2 ++
 drivers/net/mlx5/mlx5_flow_dv.c  |  2 ++
 lib/eal/include/rte_common.h     | 14 ++++++++++++++
 lib/net/rte_ip4.h                |  1 +
 lib/net/rte_ip6.h                |  1 +
 5 files changed, 20 insertions(+)

diff --git a/drivers/net/hinic/hinic_pmd_tx.c b/drivers/net/hinic/hinic_pmd_tx.c
index 22fb0bffaf..570715531d 100644
--- a/drivers/net/hinic/hinic_pmd_tx.c
+++ b/drivers/net/hinic/hinic_pmd_tx.c
@@ -725,6 +725,7 @@ hinic_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
 		rte_cpu_to_be_16(rte_be_to_cpu_16(ipv4_hdr->total_length) -
 				 rte_ipv4_hdr_len(ipv4_hdr));
 	}
+	RTE_FORCE_INIT_BARRIER(psd_hdr);
 	return rte_raw_cksum(&psd_hdr, sizeof(psd_hdr));
 }
 
@@ -743,6 +744,7 @@ hinic_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
 	else
 		psd_hdr.len = ipv6_hdr->payload_len;
 
+	RTE_FORCE_INIT_BARRIER(psd_hdr);
 	sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
 		sizeof(ipv6_hdr->src_addr) + sizeof(ipv6_hdr->dst_addr), 0);
 	sum = __rte_raw_cksum(&psd_hdr, sizeof(psd_hdr), sum);
diff --git a/drivers/net/mlx5/mlx5_flow_dv.c b/drivers/net/mlx5/mlx5_flow_dv.c
index 47f6d28410..1eeeb6747f 100644
--- a/drivers/net/mlx5/mlx5_flow_dv.c
+++ b/drivers/net/mlx5/mlx5_flow_dv.c
@@ -4445,6 +4445,8 @@ __flow_encap_decap_resource_register(struct rte_eth_dev *dev,
 			.reserve = 0,
 		}
 	};
+	RTE_FORCE_INIT_BARRIER(encap_decap_key);
+
 	struct mlx5_flow_cb_ctx ctx = {
 		.error = error,
 		.data = resource,
diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
index 00d428e295..d58e856d96 100644
--- a/lib/eal/include/rte_common.h
+++ b/lib/eal/include/rte_common.h
@@ -555,6 +555,20 @@ static void __attribute__((destructor(RTE_PRIO(prio)), used)) func(void)
 #define __rte_no_ubsan_alignment
 #endif
 
+/**
+ * Force struct initialization to prevent GCC optimization bug.
+ * GCC has a bug where it incorrectly elides struct initialization in
+ * inline functions when strict aliasing is enabled, causing reads from
+ * uninitialized memory. This memory barrier prevents the misoptimization.
+ */
+#ifdef RTE_CC_GCC
+#define RTE_FORCE_INIT_BARRIER(var) do {	\
+	asm volatile("" : "+m" (var));		\
+} while (0)
+#else
+#define RTE_FORCE_INIT_BARRIER(var)
+#endif
+
 /*********** Macros for pointer arithmetic ********/
 
 /**
diff --git a/lib/net/rte_ip4.h b/lib/net/rte_ip4.h
index 822a660cfb..a0839c584e 100644
--- a/lib/net/rte_ip4.h
+++ b/lib/net/rte_ip4.h
@@ -238,6 +238,7 @@ rte_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
 		psd_hdr.len = rte_cpu_to_be_16((uint16_t)(l3_len -
 			rte_ipv4_hdr_len(ipv4_hdr)));
 	}
+	RTE_FORCE_INIT_BARRIER(psd_hdr);
 	return rte_raw_cksum(&psd_hdr, sizeof(psd_hdr));
 }
 
diff --git a/lib/net/rte_ip6.h b/lib/net/rte_ip6.h
index d1abf1f5d5..902f100a44 100644
--- a/lib/net/rte_ip6.h
+++ b/lib/net/rte_ip6.h
@@ -572,6 +572,7 @@ rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
 	else
 		psd_hdr.len = ipv6_hdr->payload_len;
 
+	RTE_FORCE_INIT_BARRIER(psd_hdr);
 	sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
 		sizeof(ipv6_hdr->src_addr) + sizeof(ipv6_hdr->dst_addr),
 		0);
-- 
2.39.5 (Apple Git-154)