Re: drivers/iio/adc/ti-tsc2046.c:242:62: warning: taking address of packed member 'data' of class or structure 'tsc2046_adc_atom' may result in an unaligned pointer value

[Andy Shevchenko <andy.shevchenko@gmail.com>]

Seems yet another false positive from Clang.

On Mon, Jul 25, 2022 at 5:55 AM kernel test robot <lkp@intel.com> wrote:
>
> Hi Oleksij,
>
> FYI, the error/warning still remains.
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   e0dccc3b76fb35bb257b4118367a883073d7390e
> commit: 9374e8f5a38defe90bc65b2decf317c1c62d91dd iio: adc: add ADC driver for the TI TSC2046 controller
> date:   1 year, 2 months ago
> config: arm-randconfig-r025-20220724 (https://download.01.org/0day-ci/archive/20220725/202207251140.M7YAqoLC-lkp@intel.com/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 9e88cbcc403bdf82f29259ad60ff60a8fc4434a1)
> 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=9374e8f5a38defe90bc65b2decf317c1c62d91dd
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 9374e8f5a38defe90bc65b2decf317c1c62d91dd
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash drivers/iio/adc/ drivers/staging/ fs/
>
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
> >> drivers/iio/adc/ti-tsc2046.c:242:62: warning: taking address of packed member 'data' of class or structure 'tsc2046_adc_atom' may result in an unaligned pointer value [-Waddress-of-packed-member]

What the heck? The get_unaligned_*() is exactly to get unaligned data.

>            return FIELD_GET(TI_TSC2046_DATA_12BIT, get_unaligned_be16(&buf->data));
>                                                                        ^~~~~~~~~
>    include/linux/bitfield.h:108:27: note: expanded from macro 'FIELD_GET'
>                    __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");       \
>                                            ^~~~
>    include/linux/bitfield.h:52:38: note: expanded from macro '__BF_FIELD_CHECK'
>                    BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull,         \
>                                                       ^~~~
>    include/linux/build_bug.h:39:58: note: expanded from macro 'BUILD_BUG_ON_MSG'
>    #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                                             ^~~~
>    note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
>    include/linux/compiler_types.h:308:9: note: expanded from macro '__compiletime_assert'
>                    if (!(condition))                                       \
>                          ^~~~~~~~~
>    include/linux/compiler.h:56:47: note: expanded from macro 'if'
>    #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>                                                  ^~~~
>    include/linux/compiler.h:58:52: note: expanded from macro '__trace_if_var'
>    #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
>                                                       ^~~~
> >> drivers/iio/adc/ti-tsc2046.c:242:62: warning: taking address of packed member 'data' of class or structure 'tsc2046_adc_atom' may result in an unaligned pointer value [-Waddress-of-packed-member]
>            return FIELD_GET(TI_TSC2046_DATA_12BIT, get_unaligned_be16(&buf->data));
>                                                                        ^~~~~~~~~
>    include/linux/bitfield.h:108:27: note: expanded from macro 'FIELD_GET'
>                    __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");       \
>                                            ^~~~
>    include/linux/bitfield.h:52:38: note: expanded from macro '__BF_FIELD_CHECK'
>                    BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull,         \
>                                                       ^~~~
>    include/linux/build_bug.h:39:58: note: expanded from macro 'BUILD_BUG_ON_MSG'
>    #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                                             ^~~~
>    note: (skipping 2 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
>    include/linux/compiler_types.h:308:9: note: expanded from macro '__compiletime_assert'
>                    if (!(condition))                                       \
>                          ^~~~~~~~~
>    include/linux/compiler.h:56:47: note: expanded from macro 'if'
>    #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>                                                  ^~~~
>    include/linux/compiler.h:58:61: note: expanded from macro '__trace_if_var'
>    #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
>                                                                ^~~~
> >> drivers/iio/adc/ti-tsc2046.c:242:62: warning: taking address of packed member 'data' of class or structure 'tsc2046_adc_atom' may result in an unaligned pointer value [-Waddress-of-packed-member]
>            return FIELD_GET(TI_TSC2046_DATA_12BIT, get_unaligned_be16(&buf->data));
>                                                                        ^~~~~~~~~
>    include/linux/bitfield.h:108:27: note: expanded from macro 'FIELD_GET'
>                    __BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");       \
>                                            ^~~~
>    include/linux/bitfield.h:52:38: note: expanded from macro '__BF_FIELD_CHECK'
>                    BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull,         \
>                                                       ^~~~
>    include/linux/build_bug.h:39:58: note: expanded from macro 'BUILD_BUG_ON_MSG'
>    #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                                             ^~~~
>    note: (skipping 3 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
>    include/linux/compiler.h:56:47: note: expanded from macro 'if'
>    #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) )
>                                                  ^~~~
>    include/linux/compiler.h:58:86: note: expanded from macro '__trace_if_var'
>    #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
>                                                                                         ^~~~
>    include/linux/compiler.h:69:3: note: expanded from macro '__trace_if_value'
>            (cond) ?                                        \
>             ^~~~
>    3 warnings generated.
>
>
> vim +242 drivers/iio/adc/ti-tsc2046.c
>
>    239
>    240  static u16 tsc2046_adc_get_value(struct tsc2046_adc_atom *buf)
>    241  {
>  > 242          return FIELD_GET(TI_TSC2046_DATA_12BIT, get_unaligned_be16(&buf->data));
>    243  }


-- 
With Best Regards,
Andy Shevchenko