Re: [PATCH] can: mcp251xfd: silence clang's -Wunaligned-access warning

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 18.05.2022 20:43:57, Vincent Mailhol wrote:
> 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>

Thank! Applies to linux-can-next/testing.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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