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: <20210716114105.GF3@paasikivi.fi.intel.com>
Date:   Fri, 16 Jul 2021 14:41:05 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Andy Shevchenko <andy.shevchenko@...il.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>,
        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

Hi Andy,

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.

-- 
Sakari Ailus