[PATCH][next] wifi: mwl8k: Use static_assert() to check struct sizes

[Gustavo A. R. Silva]

Commit 5c4250092fad ("wifi: mwl8k: Avoid -Wflex-array-member-not-at-end
warnings") introduced tagged `struct mwl8k_cmd_pkt_hdr`. We want to
ensure that when new members need to be added to the flexible structure,
they are always included within this tagged struct.

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 <gustavoars@xxxxxxxxxx>
---
 drivers/net/wireless/marvell/mwl8k.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/wireless/marvell/mwl8k.c b/drivers/net/wireless/marvell/mwl8k.c
index b130e057370f..bab9ef37a1ab 100644
--- a/drivers/net/wireless/marvell/mwl8k.c
+++ b/drivers/net/wireless/marvell/mwl8k.c
@@ -587,6 +587,7 @@ static int mwl8k_request_firmware(struct mwl8k_priv *priv, char *fw_image,
 }
 
 struct mwl8k_cmd_pkt {
+	/* New members MUST be added within the __struct_group() macro below. */
 	__struct_group(mwl8k_cmd_pkt_hdr, hdr, __packed,
 		__le16	code;
 		__le16	length;
@@ -596,6 +597,8 @@ struct mwl8k_cmd_pkt {
 	);
 	char payload[];
 } __packed;
+static_assert(offsetof(struct mwl8k_cmd_pkt, payload) == sizeof(struct mwl8k_cmd_pkt_hdr),
+	      "struct member likely outside of __struct_group()");
 
 /*
  * Firmware loading.
-- 
2.34.1