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
2022-07-26T08:07:51Z

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