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

scott.k.mitch1
2026-01-10T01:57:27Z

From: Scott <scott_mitchell@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@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)