linux-kernel - Re: drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c:2267:16: warning: taking address of packed member 'hw_tx_obj' of class or structure 'mcp251xfd_tx_obj_load_buf::(anonymous)' may result in an unaligned pointer value

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Message-ID: <20210329064850.vh7rlwh7oapjqucj@pengutronix.de>
Date:   Mon, 29 Mar 2021 08:48:50 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: Re: drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c:2267:16: warning:
 taking address of packed member 'hw_tx_obj' of class or structure
 'mcp251xfd_tx_obj_load_buf::(anonymous)' may result in an unaligned pointer
 value

On 27.03.2021 18:16:14, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   0f4498cef9f5cd18d7c6639a2a902ec1edc5be4e
> commit: eb79a267c9b3e608e7762a1b221428f37ace3aa3 can: mcp251xfd: rename all remaining occurrence to mcp251xfd
> date:   6 months ago
> config: mips-randconfig-r035-20210327 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project d50fe9f0d6b9ee61df8830a67ea0a33c27a637e7)
> 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 mips cross compiling tool for clang build
>         # apt-get install binutils-mips-linux-gnu
>         # 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 attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=mips 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):

[...]

> >> drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c:2267:16: warning: taking address of packed member 'hw_tx_obj' of class or structure 'mcp251xfd_tx_obj_load_buf::(anonymous)' may result in an unaligned pointer value [-Waddress-of-packed-member]
>                    hw_tx_obj = &load_buf->crc.hw_tx_obj;
>                                 ^~~~~~~~~~~~~~~~~~~~~~~
>    drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c:2269:16: warning: taking address of packed member 'hw_tx_obj' of class or structure 'mcp251xfd_tx_obj_load_buf::(anonymous)' may result in an unaligned pointer value [-Waddress-of-packed-member]
>                    hw_tx_obj = &load_buf->nocrc.hw_tx_obj;
>                                 ^~~~~~~~~~~~~~~~~~~~~~~~~
>    4 warnings and 1 error generated.

That warning is technically correct, hw_tx_obj is an unaligned pointer in
the first warning, but...

> vim +2267 drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
> 
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2215  static void
> eb79a267c9b3e6 drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c Marc Kleine-Budde 2020-09-30  2216  mcp251xfd_tx_obj_from_skb(const struct mcp251xfd_priv *priv,
> eb79a267c9b3e6 drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c Marc Kleine-Budde 2020-09-30  2217  			  struct mcp251xfd_tx_obj *tx_obj,
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2218  			  const struct sk_buff *skb,
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2219  			  unsigned int seq)
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2220  {
[...]
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2265  	load_buf = &tx_obj->buf;
> eb79a267c9b3e6 drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c Marc Kleine-Budde 2020-09-30  2266  	if (priv->devtype_data.quirks & MCP251XFD_QUIRK_CRC_TX)
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18 @2267  		hw_tx_obj = &load_buf->crc.hw_tx_obj;
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2268  	else
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2269  		hw_tx_obj = &load_buf->nocrc.hw_tx_obj;
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2270  
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2271  	put_unaligned_le32(id, &hw_tx_obj->id);
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2272  	put_unaligned_le32(flags, &hw_tx_obj->flags);
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2273  
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2274  	/* Clear data at end of CAN frame */
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2275  	offset = round_down(cfd->len, sizeof(u32));
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2276  	len = round_up(can_dlc2len(dlc), sizeof(u32)) - offset;
> eb79a267c9b3e6 drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c Marc Kleine-Budde 2020-09-30  2277  	if (MCP251XFD_SANITIZE_CAN && len)
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2278  		memset(hw_tx_obj->data + offset, 0x0, len);
> 55e5b97f003e85 drivers/net/can/spi/mcp25xxfd/mcp25xxfd-core.c Marc Kleine-Budde 2020-09-18  2279  	memcpy(hw_tx_obj->data, cfd->data, cfd->len);

...it's only accessed via put_unaligned_* and memset()/memcpy().

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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