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

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Message-ID: <c52a52d9-a9e0-5020-80fe-4aada39035d3@acm.org>
Date:   Wed, 28 Jul 2021 14:37:20 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Dan Carpenter <dan.carpenter@...cle.com>, dsterba@...e.cz,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 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 { }. BTW, my understanding is that neither the C standard nor the 
C++ standard guarantee anything about initialization of padding bytes 
nor about the initialization of unnamed bitfields for stack variables 
when using aggregate initialization.

Bart.