Messages in this thread Patch in this message | | | From | Vincent Mailhol <> | Subject | [PATCH] can: mcp251xfd: silence clang's -Wunaligned-access warning | Date | Wed, 18 May 2022 20:43:57 +0900 |
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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@wanadoo.fr> --- 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
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