netdev - [PATCH net 3/4] can: ems_usb: fix clang's -Wunaligned-access warning

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Message-Id: <20220809075317.1549323-4-mkl@pengutronix.de>
Date:   Tue,  9 Aug 2022 09:53:16 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        kernel@...gutronix.de, Marc Kleine-Budde <mkl@...gutronix.de>,
        Gerhard Uttenthaler <uttenthaler@...-wuensche.com>,
        Sebastian Haas <haas@...-wuensche.com>
Subject: [PATCH net 3/4] can: ems_usb: fix clang's -Wunaligned-access warning

clang emits a -Wunaligned-access warning on struct __packed
ems_cpc_msg.

The reason is that the anonymous union msg (not declared as packed) is
being packed right after some non naturally aligned variables (3*8
bits + 2*32) inside a packed struct:

| struct __packed ems_cpc_msg {
| 	u8 type;	/* type of message */
| 	u8 length;	/* length of data within union 'msg' */
| 	u8 msgid;	/* confirmation handle */
| 	__le32 ts_sec;	/* timestamp in seconds */
| 	__le32 ts_nsec;	/* timestamp in nano seconds */
|	/* ^ not naturally aligned */
|
| 	union {
| 	/* ^ not declared as packed */
| 		u8 generic[64];
| 		struct cpc_can_msg can_msg;
| 		struct cpc_can_params can_params;
| 		struct cpc_confirm confirmation;
| 		struct cpc_overrun overrun;
| 		struct cpc_can_error error;
| 		struct cpc_can_err_counter err_counter;
| 		u8 can_state;
| 	} msg;
| };

Starting from LLVM 14, having an unpacked struct nested in a packed
struct triggers a warning. c.f. [1].

Fix the warning by marking the anonymous union as packed.

[1] https://github.com/llvm/llvm-project/issues/55520

Fixes: 702171adeed3 ("ems_usb: Added support for EMS CPC-USB/ARM7 CAN/USB interface")
Link: https://lore.kernel.org/all/20220802094021.959858-1-mkl@pengutronix.de
Cc: Gerhard Uttenthaler <uttenthaler@...-wuensche.com>
Cc: Sebastian Haas <haas@...-wuensche.com>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 drivers/net/can/usb/ems_usb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/usb/ems_usb.c b/drivers/net/can/usb/ems_usb.c
index d1e1a459c045..d31191686a54 100644
--- a/drivers/net/can/usb/ems_usb.c
+++ b/drivers/net/can/usb/ems_usb.c
@@ -195,7 +195,7 @@ struct __packed ems_cpc_msg {
 	__le32 ts_sec;	/* timestamp in seconds */
 	__le32 ts_nsec;	/* timestamp in nano seconds */
 
-	union {
+	union __packed {
 		u8 generic[64];
 		struct cpc_can_msg can_msg;
 		struct cpc_can_params can_params;
-- 
2.35.1