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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Message-ID: <YPF3m01nYlt3On7V@smile.fi.intel.com>
Date:   Fri, 16 Jul 2021 15:12:11 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     kernel test robot <lkp@...el.com>,
        Nick Desaulniers <nick.desaulniers@...il.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>
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

On Fri, Jul 16, 2021 at 02:41:05PM +0300, Sakari Ailus wrote:
> On Wed, Jul 14, 2021 at 10:45:26PM +0300, Andy Shevchenko wrote:
> > > >> 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?
> 
> It's packed since we wanted to avoid having holes in the structs. There are
> other ways to do that but it's ABI dependent and is prone to human errors,
> too.

What holes can you think about in the above mention structure?

In case if you are going to extend it you will need anyway changes somewhere
else as well.

-- 
With Best Regards,
Andy Shevchenko