linux-kernel - Re: drivers/media/v4l2-core/v4l2-ioctl.c:303:28: warning: taking address of packed member 'pixelformat' of class or structure 'v4l2_pix_format_mplane' may result in an unaligned pointer value

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Date:   Wed, 14 Jul 2021 22:45:26 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     kernel test robot <lkp@...el.com>,
        Nick Desaulniers <nick.desaulniers@...il.com>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        kbuild-all@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: drivers/media/v4l2-core/v4l2-ioctl.c:303:28: warning: taking
 address of packed member 'pixelformat' of class or structure
 'v4l2_pix_format_mplane' may result in an unaligned pointer value

+Cc: Nick. Nick, any recommendations on how to fix this in the best
possible way?

On Wed, Jul 14, 2021 at 8:58 PM kernel test robot <lkp@...el.com> wrote:
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   8096acd7442e613fad0354fc8dfdb2003cceea0b
> commit: e927e1e0f0dd3e353d5556503a71484008692c82 v4l: ioctl: Use %p4cc printk modifier to print FourCC codes
> date:   5 months ago
> config: mips-randconfig-r004-20210714 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 8d69635ed9ecf36fd0ca85906bfde17949671cbe)
> 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=e927e1e0f0dd3e353d5556503a71484008692c82
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout e927e1e0f0dd3e353d5556503a71484008692c82
>         # 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/media/v4l2-core/v4l2-ioctl.c:303:28: warning: taking address of packed member 'pixelformat' of class or structure 'v4l2_pix_format_mplane' may result in an unaligned pointer value [-Waddress-of-packed-member]
>                            mp->width, mp->height, &mp->pixelformat,

This seems unsolvable without copying a value.

> >> drivers/media/v4l2-core/v4l2-ioctl.c:347:37: warning: taking address of packed member 'pixelformat' of class or structure 'v4l2_sdr_format' may result in an unaligned pointer value [-Waddress-of-packed-member]

Why is it packed in the first place? Is it used on unaligned addresses
in other structures? But even so, why should it matter?

> >> drivers/media/v4l2-core/v4l2-ioctl.c:353:5: warning: taking address of packed member 'dataformat' of class or structure 'v4l2_meta_format' may result in an unaligned pointer value [-Waddress-of-packed-member]
>                            &meta->dataformat, meta->buffersize);

Ditto.

-- 
With Best Regards,
Andy Shevchenko