[PATCH v2][next] rtc: Avoid a couple of -Wflex-array-member-not-at-end warnings

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

Use the `DEFINE_RAW_FLEX()` helper for an on-stack definition 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/rtc/rtc-cros-ec.c:62:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/rtc/rtc-cros-ec.c:40:40: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Change in v2:
 - Cast to `struct ec_response_rtc *`, instead of using memcpy(). (Tzung-Bi Shih)

v1:
 - Link: https://lore.kernel.org/linux-hardening/Z9N8BsVJF-s6Hcvd@kspp/

 drivers/rtc/rtc-cros-ec.c | 30 ++++++++++++------------------
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/drivers/rtc/rtc-cros-ec.c b/drivers/rtc/rtc-cros-ec.c
index 865c2e82c7a5..e956505a06fb 100644
--- a/drivers/rtc/rtc-cros-ec.c
+++ b/drivers/rtc/rtc-cros-ec.c
@@ -35,21 +35,18 @@ struct cros_ec_rtc {
 static int cros_ec_rtc_get(struct cros_ec_device *cros_ec, u32 command,
 			   u32 *response)
 {
+	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
+			sizeof(struct ec_response_rtc));
 	int ret;
-	struct {
-		struct cros_ec_command msg;
-		struct ec_response_rtc data;
-	} __packed msg;
 
-	memset(&msg, 0, sizeof(msg));
-	msg.msg.command = command;
-	msg.msg.insize = sizeof(msg.data);
+	msg->command = command;
+	msg->insize = sizeof(struct ec_response_rtc);
 
-	ret = cros_ec_cmd_xfer_status(cros_ec, &msg.msg);
+	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
 	if (ret < 0)
 		return ret;
 
-	*response = msg.data.time;
+	*response = ((struct ec_response_rtc *)msg->data)->time;
 
 	return 0;
 }
@@ -57,18 +54,15 @@ static int cros_ec_rtc_get(struct cros_ec_device *cros_ec, u32 command,
 static int cros_ec_rtc_set(struct cros_ec_device *cros_ec, u32 command,
 			   u32 param)
 {
+	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
+			sizeof(struct ec_response_rtc));
 	int ret;
-	struct {
-		struct cros_ec_command msg;
-		struct ec_response_rtc data;
-	} __packed msg;
 
-	memset(&msg, 0, sizeof(msg));
-	msg.msg.command = command;
-	msg.msg.outsize = sizeof(msg.data);
-	msg.data.time = param;
+	msg->command = command;
+	msg->outsize = sizeof(struct ec_response_rtc);
+	((struct ec_response_rtc *)msg->data)->time = param;
 
-	ret = cros_ec_cmd_xfer_status(cros_ec, &msg.msg);
+	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
 	if (ret < 0)
 		return ret;
 	return 0;
-- 
2.43.0