Subject: [PATCH][next] net/smc: Use static_assert() to check struct sizes

From: "Gustavo A. R. Silva" <[email-masked]>
Date: Thu, 8 Aug 2024 16:07:54 -0600

Commit 9748dbc9f265 ("net/smc: Avoid -Wflex-array-member-not-at-end
warnings") introduced tagged `struct smc_clc_v2_extension_fixed` and
`struct smc_clc_smcd_v2_extension_fixed`. We want to ensure that when
new members need to be added to the flexible structures, they are
always included within these tagged structs.

So, we use `static_assert()` to ensure that the memory layout for
both the flexible structure and the tagged struct is the same after
any changes.

Signed-off-by: Gustavo A. R. Silva <[email-masked]>
---
 net/smc/smc_clc.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/smc/smc_clc.h b/net/smc/smc_clc.h
index 467effb50cd6..5625fda2960b 100644
--- a/net/smc/smc_clc.h
+++ b/net/smc/smc_clc.h
@@ -145,6 +145,8 @@ struct smc_clc_v2_extension {
 	);
 	u8 user_eids[][SMC_MAX_EID_LEN];
 };
+static_assert(offsetof(struct smc_clc_v2_extension, user_eids) == sizeof(struct smc_clc_v2_extension_fixed),
+	      "struct member likely outside of struct_group_tagged()");
 
 struct smc_clc_msg_proposal_prefix {	/* prefix part of clc proposal message*/
 	__be32 outgoing_subnet;	/* subnet mask */
@@ -169,6 +171,8 @@ struct smc_clc_smcd_v2_extension {
 	);
 	struct smc_clc_smcd_gid_chid gidchid[];
 };
+static_assert(offsetof(struct smc_clc_smcd_v2_extension, gidchid) == sizeof(struct smc_clc_smcd_v2_extension_fixed),
+	      "struct member likely outside of struct_group_tagged()");
 
 struct smc_clc_msg_proposal {	/* clc proposal message sent by Linux */
 	struct smc_clc_msg_hdr hdr;
-- 
2.34.1