Re: drivers/net/can/spi/mcp251xfd/mcp251xfd.h:481:34: warning: field hw_tx_obj within 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:479:2)' is less aligned than 'struct mcp251xfd_hw_tx_obj_raw' and is usually due to ...

From: Marc Kleine-Budde
Date: Wed May 18 2022 - 03:05:39 EST

On 18.05.2022 14:45:33, kernel test robot wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: 210e04ff768142b96452030c4c2627512b30ad95
> commit: eb79a267c9b3e608e7762a1b221428f37ace3aa3 can: mcp251xfd: rename all remaining occurrence to mcp251xfd
> date: 1 year, 8 months ago
> config: arm-randconfig-c002-20220518 (https://download.01.org/0day-ci/archive/20220518/202205181414.n8QRDe8k-lkp@xxxxxxxxx/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 853fa8ee225edf2d0de94b0dcbd31bea916e825e)
> reproduce (this is a W=1 build):
> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> # install arm cross compiling tool for clang build
> # apt-get install binutils-arm-linux-gnueabi
> # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=eb79a267c9b3e608e7762a1b221428f37ace3aa3
> git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> git fetch --no-tags linus master
> git checkout eb79a267c9b3e608e7762a1b221428f37ace3aa3
> # save the config file
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
>
> All warnings (new ones prefixed by >>):
>
> >> drivers/net/can/spi/mcp251xfd/mcp251xfd.h:481:34: warning: field hw_tx_obj within 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:479:2)' is less aligned than 'struct mcp251xfd_hw_tx_obj_raw' and is usually due to 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:479:2)' being packed, which can lead to unaligned accesses [-Wunaligned-access]
> struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
> ^
> drivers/net/can/spi/mcp251xfd/mcp251xfd.h:485:34: warning: field hw_tx_obj within 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:483:2)' is less aligned than 'struct mcp251xfd_hw_tx_obj_raw' and is usually due to 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:483:2)' being packed, which can lead to unaligned accesses [-Wunaligned-access]
> struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
> ^
> drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c:511:1: warning: unused function 'mcp251xfd_chip_set_mode_nowait' [-Wunused-function]
> mcp251xfd_chip_set_mode_nowait(const struct mcp251xfd_priv *priv,
> ^
> 3 warnings generated.
> --
> >> drivers/net/can/spi/mcp251xfd/mcp251xfd.h:481:34: warning: field hw_tx_obj within 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:479:2)' is less aligned than 'struct mcp251xfd_hw_tx_obj_raw' and is usually due to 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:479:2)' being packed, which can lead to unaligned accesses [-Wunaligned-access]
> struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
> ^
> drivers/net/can/spi/mcp251xfd/mcp251xfd.h:485:34: warning: field hw_tx_obj within 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:483:2)' is less aligned than 'struct mcp251xfd_hw_tx_obj_raw' and is usually due to 'struct mcp251xfd_tx_obj_load_buf::(unnamed at drivers/net/can/spi/mcp251xfd/mcp251xfd.h:483:2)' being packed, which can lead to unaligned accesses [-Wunaligned-access]
> struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
> ^
> 2 warnings generated.
>
>
> vim +481 drivers/net/can/spi/mcp251xfd/mcp251xfd.h
>
> 477
> 478 union mcp251xfd_tx_obj_load_buf {
> 479 struct __packed {
> 480 struct mcp251xfd_buf_cmd cmd;
> > 481 struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
> 482 } nocrc;
> 483 struct __packed {
> 484 struct mcp251xfd_buf_cmd_crc cmd;
> 485 struct mcp251xfd_hw_tx_obj_raw hw_tx_obj;
> 486 __be16 crc;
> 487 } crc;
> 488 } ____cacheline_aligned;
> 489

The structure layout is intentional as it describes the hardware
messages on the SPI bus. The functions accessing these structs use
appropriate put_unaligned_*() functions.

How to properly annotate these structs to silence the warnings?

Marc

--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
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