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
Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
---
Actually, I do not have llvm 14 installed so I am not able to test
(this check was introduced in v14). But as explained in [1], adding
__packed should fix the warning.
Because this is a false positive, I did not add a Fixes tag, nor a
Reported-by: kernel test robot.
---
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 1d43bccc29bf..2b0309fedfac 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd.h
@@ -441,7 +441,7 @@ 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
