linux-kernel - Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy() region

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Message-ID: <20210729082039.GX25548@kadam>
Date:   Thu, 29 Jul 2021 11:20:39 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     dsterba@...e.cz, Bart Van Assche <bvanassche@....org>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com,
        nborisov@...e.com
Subject: Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy()
 region

On Thu, Jul 29, 2021 at 07:56:27AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Jul 28, 2021 at 11:37:30PM +0200, David Sterba wrote:
> > On Wed, Jul 28, 2021 at 02:37:20PM -0700, Bart Van Assche wrote:
> > > On 7/28/21 2:14 AM, Dan Carpenter wrote:
> > > > On Wed, Jul 28, 2021 at 10:59:22AM +0200, David Sterba wrote:
> > > >>>   drivers/media/platform/omap3isp/ispstat.c |  5 +--
> > > >>>   include/uapi/linux/omap3isp.h             | 44 +++++++++++++++++------
> > > >>>   2 files changed, 36 insertions(+), 13 deletions(-)
> > > >>>
> > > >>> diff --git a/drivers/media/platform/omap3isp/ispstat.c b/drivers/media/platform/omap3isp/ispstat.c
> > > >>> index 5b9b57f4d9bf..ea8222fed38e 100644
> > > >>> --- a/drivers/media/platform/omap3isp/ispstat.c
> > > >>> +++ b/drivers/media/platform/omap3isp/ispstat.c
> > > >>> @@ -512,7 +512,7 @@ int omap3isp_stat_request_statistics(struct ispstat *stat,
> > > >>>   int omap3isp_stat_request_statistics_time32(struct ispstat *stat,
> > > >>>   					struct omap3isp_stat_data_time32 *data)
> > > >>>   {
> > > >>> -	struct omap3isp_stat_data data64;
> > > >>> +	struct omap3isp_stat_data data64 = { };
> > > >>
> > > >> Should this be { 0 } ?
> > > >>
> > > >> We've seen patches trying to switch from { 0 } to {  } but the answer
> > > >> was that { 0 } is supposed to be used,
> > > >> http://www.ex-parrot.com/~chris/random/initialise.html 
> > > >>
> > > >> (from https://lore.kernel.org/lkml/fbddb15a-6e46-3f21-23ba-b18f66e3448a@suse.com/ )
> > > > 
> > > > In the kernel we don't care about portability so much.  Use the = { }
> > > > GCC extension.  If the first member of the struct is a pointer then
> > > > Sparse will complain about = { 0 }.
> > > 
> > > +1 for { }.
> > 
> > Oh, I thought the tendency is is to use { 0 } because that can also
> > intialize the compound members, by a "scalar 0" as it appears in the
> > code.
> > 
> 
> Holes in the structure might not be initialized to anything if you do
> either one of these as well.
> 
> Or did we finally prove that is not the case?  I can not remember
> anymore...

Yep.  The C11 spec says that struct holes are initialized.

https://lore.kernel.org/netdev/20200731140452.GE24045@ziepe.ca/

What doesn't initialize struct holes is assignments:

	struct foo foo = *bar;

regards,
dan carpenter