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

From: Marc Kleine-Budde
Date: Mon Mar 29 2021 - 03:19:32 EST

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@xxxxxxxxx>
>
> 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

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