Re: [PATCH] media: cedrus: don't initialize pointers with zero

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On 12/07/2018 12:31 PM, Mauro Carvalho Chehab wrote:
> Em Fri, 7 Dec 2018 12:14:50 +0100
> Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:
> 
>> On 12/07/2018 11:56 AM, Mauro Carvalho Chehab wrote:
>>> A common mistake is to assume that initializing a var with:
>>> 	struct foo f = { 0 };
>>>
>>> Would initialize a zeroed struct. Actually, what this does is
>>> to initialize the first element of the struct to zero.
>>>
>>> According to C99 Standard 6.7.8.21:
>>>
>>>     "If there are fewer initializers in a brace-enclosed
>>>      list than there are elements or members of an aggregate,
>>>      or fewer characters in a string literal used to initialize
>>>      an array of known size than there are elements in the array,
>>>      the remainder of the aggregate shall be initialized implicitly
>>>      the same as objects that have static storage duration."
>>>
>>> So, in practice, it could zero the entire struct, but, if the
>>> first element is not an integer, it will produce warnings:
>>>
>>> 	drivers/staging/media/sunxi/cedrus/cedrus.c:drivers/staging/media/sunxi/cedrus/cedrus.c:78:49:  warning: Using plain integer as NULL pointer
>>> 	drivers/staging/media/sunxi/cedrus/cedrus_dec.c:drivers/staging/media/sunxi/cedrus/cedrus_dec.c:29:35:  warning: Using plain integer as NULL pointer
>>>
>>> A proper way to initialize it with gcc is to use:
>>>
>>> 	struct foo f = { };
>>>
>>> But that seems to be a gcc extension. So, I decided to check upstream  
>>
>> No, this is not a gcc extension. It's part of the latest C standard.
> 
> Sure? Where the C standard spec states that? I've been seeking for
> such info for a while, as '= {}' is also my personal preference.

I believe it was added in C11, but I've loaned the book that stated
that to someone else, so I can't check.

In any case, it's used everywhere:

git grep '= *{ *}' drivers/

So it is really pointless to *not* use it.

Regards,

	Hans

> I tried to build the Kernel with clang, just to be sure that this
> won't cause issues with the clang support, but, unfortunately, the
> clang compiler (not even the upstream version) is able to build
> the upstream Kernel yet, as it lacks asm-goto support (there is an
> OOT patch for llvm solving it - but it sounds too much effort for
> my time to have to build llvm from their sources just for a simple
> check like this).
> 
>> It's used all over in the kernel, so please use {} instead of { NULL }.
>>
>> Personally I think {} is a fantastic invention and I wish C++ had it as
>> well.
> 
> Fully agreed on that.
> 
>>
>> Regards,
>>
>> 	Hans
>>
>>> what's the most commonly pattern. The gcc pattern has about 2000 entries:
>>>
>>> 	$ git grep -E "=\s*\{\s*\}"|wc -l
>>> 	1951
>>>
>>> The standard-C compliant pattern has about 2500 entries:
>>>
>>> 	$ git grep -E "=\s*\{\s*NULL\s*\}"|wc -l
>>> 	137
>>> 	$ git grep -E "=\s*\{\s*0\s*\}"|wc -l
>>> 	2323
>>>
>>> So, let's initialize those structs with:
>>> 	 = { NULL }
>>>
>>> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx>
>>> ---
>>>  drivers/staging/media/sunxi/cedrus/cedrus.c     | 2 +-
>>>  drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 2 +-
>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c b/drivers/staging/media/sunxi/cedrus/cedrus.c
>>> index b538eb0321d8..44c45c687503 100644
>>> --- a/drivers/staging/media/sunxi/cedrus/cedrus.c
>>> +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c
>>> @@ -75,7 +75,7 @@ static int cedrus_init_ctrls(struct cedrus_dev *dev, struct cedrus_ctx *ctx)
>>>  	memset(ctx->ctrls, 0, ctrl_size);
>>>  
>>>  	for (i = 0; i < CEDRUS_CONTROLS_COUNT; i++) {
>>> -		struct v4l2_ctrl_config cfg = { 0 };
>>> +		struct v4l2_ctrl_config cfg = { NULL };
>>>  
>>>  		cfg.elem_size = cedrus_controls[i].elem_size;
>>>  		cfg.id = cedrus_controls[i].id;
>>> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
>>> index e40180a33951..4099a42dba2d 100644
>>> --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
>>> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
>>> @@ -26,7 +26,7 @@ void cedrus_device_run(void *priv)
>>>  {
>>>  	struct cedrus_ctx *ctx = priv;
>>>  	struct cedrus_dev *dev = ctx->dev;
>>> -	struct cedrus_run run = { 0 };
>>> +	struct cedrus_run run = { NULL };
>>>  	struct media_request *src_req;
>>>  	unsigned long flags;
>>>  
>>>   
>>
> 
> 
> 
> Thanks,
> Mauro
> 




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