[PATCH v2][next] watchdog: cros-ec: Avoid -Wflex-array-member-not-at-end warning

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the `DEFINE_RAW_FLEX()` helper for on-stack definitions of
a flexible structure where the size of the flexible-array member
is known at compile-time, and refactor the rest of the code,
accordingly.

So, with these changes, fix the following warning:

drivers/watchdog/cros_ec_wdt.c:29:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes v2:
 - Fix truncated line in changelog text. (Tzung-Bi)
 - Update variable name: s/buf/msg (Tzung-Bi)
 - Cast to structs instead of union. (Tzung-Bi)
 - Add RB tag.

v1:
 - Link: https://lore.kernel.org/linux-hardening/Z-SBITmMfwjocYwL@kspp/

 drivers/watchdog/cros_ec_wdt.c | 30 +++++++++++++-----------------
 1 file changed, 13 insertions(+), 17 deletions(-)

diff --git a/drivers/watchdog/cros_ec_wdt.c b/drivers/watchdog/cros_ec_wdt.c
index 716c23f4388c..9ffe7f505645 100644
--- a/drivers/watchdog/cros_ec_wdt.c
+++ b/drivers/watchdog/cros_ec_wdt.c
@@ -25,26 +25,22 @@ static int cros_ec_wdt_send_cmd(struct cros_ec_device *cros_ec,
 				union cros_ec_wdt_data *arg)
 {
 	int ret;
-	struct {
-		struct cros_ec_command msg;
-		union cros_ec_wdt_data data;
-	} __packed buf = {
-		.msg = {
-			.version = 0,
-			.command = EC_CMD_HANG_DETECT,
-			.insize  = (arg->req.command == EC_HANG_DETECT_CMD_GET_STATUS) ?
-				   sizeof(struct ec_response_hang_detect) :
-				   0,
-			.outsize = sizeof(struct ec_params_hang_detect),
-		},
-		.data.req = arg->req
-	};
-
-	ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
+	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
+			sizeof(union cros_ec_wdt_data));
+
+	msg->version = 0;
+	msg->command = EC_CMD_HANG_DETECT;
+	msg->insize  = (arg->req.command == EC_HANG_DETECT_CMD_GET_STATUS) ?
+		   sizeof(struct ec_response_hang_detect) :
+		   0;
+	msg->outsize = sizeof(struct ec_params_hang_detect);
+	*(struct ec_params_hang_detect *)msg->data = arg->req;
+
+	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
 	if (ret < 0)
 		return ret;
 
-	arg->resp = buf.data.resp;
+	arg->resp = *(struct ec_response_hang_detect *)msg->data;
 
 	return 0;
 }
-- 
2.43.0