[PATCH AUTOSEL 5.15 097/109] can: mcp251xfd: silence clang's -Wunaligned-access warning

Sasha Levin
2022-05-30T14:21:20Z

From: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

[ Upstream commit 1a6dd9996699889313327be03981716a8337656b ]

clang emits a -Wunaligned-access warning on union
mcp251xfd_tx_ojb_load_buf.

The reason is that field hw_tx_obj (not declared as packed) is being
packed right after a 16 bits field inside a packed struct:

| union mcp251xfd_tx_obj_load_buf {
| struct __packed {
| struct mcp251xfd_buf_cmd cmd;
| /* ^ 16 bits fields */
| struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
| /* ^ not declared as packed */
| } nocrc;
| struct __packed {
| struct mcp251xfd_buf_cmd_crc cmd;
| struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
| __be16 crc;
| } crc;
| } ____cacheline_aligned;

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

This is a false positive because the field is always being accessed
with the relevant put_unaligned_*() function. Adding __packed to the
structure declaration silences the warning.

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

Link: https://lore.kernel.org/all/20220518114357.55452-1-mailhol.vincent@wanadoo.fr
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reported-by: kernel test robot <lkp@intel.com>
Tested-by: Nathan Chancellor <nathan@kernel.org> # build
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/can/spi/mcp251xfd/mcp251xfd.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
index 0f322dabaf65..281856eea2ef 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
@@ -433,7 +433,7 @@ struct mcp251xfd_hw_tef_obj {
/* The tx_obj_raw version is used in spi async, i.e. without
* regmap. We have to take care of endianness ourselves.
*/
-struct mcp251xfd_hw_tx_obj_raw {
+struct __packed mcp251xfd_hw_tx_obj_raw {
__le32 id;
__le32 flags;
u8 data[sizeof_field(struct canfd_frame, data)];
--
2.35.1