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

From: Nathan Chancellor
Date: Tue Jul 26 2022 - 11:17:26 EST

On Tue, Jul 26, 2022 at 10:07:09AM +0200, Andy Shevchenko wrote:
> Seems yet another false positive from Clang.

This warning should not show up because it is disabled in the main
Makefile. Unfortunately, a recent change in clang made '-mtune' warn
when it is not supported in the backend, which is the case for ARM:

https://github.com/ClangBuiltLinux/linux/issues/1674

As a result, all subsequent cc-option calls fail, which was the root
cause of this warning last time, just with MIPS:

https://lore.kernel.org/YenXz+RznXBuJMSR@dev-arch.archlinux-ax161/

Intel folks, could you update your version of clang or add this
particular warning to your blocklist? It should be resolved with
https://github.com/llvm/llvm-project/commit/1d23f6c5a4f6ebb101c282f8f506588fe4d9e92f.

Cheers,
Nathan

> On Mon, Jul 25, 2022 at 5:55 AM kernel test robot <lkp@xxxxxxxxx> 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@xxxxxxxxx/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@xxxxxxxxx>
> >
> > 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