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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