From: Petr Mladek <pmladek@suse.com> To: Sakari Ailus <sakari.ailus@linux.intel.com> Cc: Andy Shevchenko <andy.shevchenko@gmail.com>, kernel test robot <lkp@intel.com>, Nick Desaulniers <nick.desaulniers@gmail.com>, clang-built-linux <clang-built-linux@googlegroups.com>, kbuild-all@lists.01.org, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Thomas Zimmermann <tzimmermann@suse.de> 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 Date: Thu, 26 Aug 2021 15:22:51 +0200 [thread overview] Message-ID: <YSeVq7nvVKgCL4HL@alley> (raw) In-Reply-To: <20210819081053.GW3@paasikivi.fi.intel.com> On Thu 2021-08-19 11:10:53, Sakari Ailus wrote: > On Fri, Jul 16, 2021 at 03:12:11PM +0300, Andy Shevchenko wrote: > > 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] > > > > Is there any plan to fix this, please? > > > > 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? > > Probably not that one but it has happened in the past that the struct > memory layout has been unintentionally different in different ABIs and that > has not been the intention, but rather a bug. What kind of bugs did the different ABI caused, please? Incompatibly between 3rd party drivers that were built with different compilers? I am not familiar with these problems. I wonder if there is a better solution. I guess that it might be a common problem affecting most drivers. Anyway, the non-aligned struct members might create slower code. > Packing has been added in newer structs to avoid that. And this smells with cargo-cult programming. People might make all new structures packed even when it is not really needed. Best Regards, Petr
WARNING: multiple messages have this Message-ID (diff)
From: Petr Mladek <pmladek@suse.com> To: kbuild-all@lists.01.org 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 Date: Thu, 26 Aug 2021 15:22:51 +0200 [thread overview] Message-ID: <YSeVq7nvVKgCL4HL@alley> (raw) In-Reply-To: <20210819081053.GW3@paasikivi.fi.intel.com> [-- Attachment #1: Type: text/plain, Size: 1709 bytes --] On Thu 2021-08-19 11:10:53, Sakari Ailus wrote: > On Fri, Jul 16, 2021 at 03:12:11PM +0300, Andy Shevchenko wrote: > > 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] > > > > Is there any plan to fix this, please? > > > > 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? > > Probably not that one but it has happened in the past that the struct > memory layout has been unintentionally different in different ABIs and that > has not been the intention, but rather a bug. What kind of bugs did the different ABI caused, please? Incompatibly between 3rd party drivers that were built with different compilers? I am not familiar with these problems. I wonder if there is a better solution. I guess that it might be a common problem affecting most drivers. Anyway, the non-aligned struct members might create slower code. > Packing has been added in newer structs to avoid that. And this smells with cargo-cult programming. People might make all new structures packed even when it is not really needed. Best Regards, Petr
next prev parent reply other threads:[~2021-08-26 13:22 UTC|newest] Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-14 17:55 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 kernel test robot 2021-07-14 17:55 ` kernel test robot 2021-07-14 19:45 ` Andy Shevchenko 2021-07-14 19:45 ` Andy Shevchenko 2021-07-16 11:41 ` Sakari Ailus 2021-07-16 11:41 ` Sakari Ailus 2021-07-16 12:12 ` Andy Shevchenko 2021-07-16 12:12 ` Andy Shevchenko 2021-08-19 8:10 ` Sakari Ailus 2021-08-19 8:10 ` Sakari Ailus 2021-08-26 13:22 ` Petr Mladek [this message] 2021-08-26 13:22 ` Petr Mladek 2021-11-04 22:21 kernel test robot 2021-11-04 22:21 ` kernel test robot 2021-11-05 10:21 ` Andy Shevchenko 2021-11-05 10:21 ` Andy Shevchenko 2022-01-08 10:33 kernel test robot 2022-01-08 10:33 ` kernel test robot 2022-01-09 14:26 ` Andy Shevchenko 2022-01-09 14:26 ` Andy Shevchenko 2022-01-10 19:44 ` Nick Desaulniers 2022-01-10 19:44 ` Nick Desaulniers 2022-01-10 20:49 ` Andy Shevchenko 2022-01-10 20:49 ` Andy Shevchenko 2022-01-10 21:22 ` Nick Desaulniers 2022-01-10 21:22 ` Nick Desaulniers 2022-01-17 3:40 kernel test robot 2022-01-17 3:40 ` kernel test robot
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