linux-kernel - Re: [PATCH] ath9k: initialize arrays at compile time

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Message-ID: <c290ae27-9e4a-96ed-d8d6-a8b8bf8d0181@redhat.com>
Date:   Wed, 23 Mar 2022 06:13:25 -0700
From:   Tom Rix <trix@...hat.com>
To:     Joe Perches <joe@...ches.com>,
        Sebastian Gottschall <s.gottschall@...media-net.de>,
        John Crispin <john@...ozen.org>, toke@...e.dk,
        kvalo@...nel.org, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ath9k: initialize arrays at compile time


On 3/20/22 10:36 AM, Joe Perches wrote:
> On Sun, 2022-03-20 at 18:17 +0100, Sebastian Gottschall wrote:
>> Am 20.03.2022 um 17:48 schrieb John Crispin:
>>>
>>> On 20.03.22 16:20, trix@...hat.com wrote:
>>>> array[size] = { 0 };
>>> should this not be array[size] = { }; ?!
>>>
>>> If I recall correctly { 0 } will only set the first element of the
>>> struct/array to 0 and leave random data in all others elements
>>>
>>>      John
>> You are right, john
> No.  The patch is fine.
>
> Though generally the newer code in the kernel uses
>
> 	type dec[size] = {};
>
> to initialize stack arrays.
>
> array stack declarations not using 0
>
> $ git grep -P '^\t(?:\w++\s*){1,2}\[\s*\w+\s*\]\s*=\s*\{\s*\};' -- '*.c' | wc -l
> 213
>
> array stack declarations using 0
>
> $ git grep -P '^\t(?:\w++\s*){1,2}\[\s*\w+\s*\]\s*=\s*\{\s*0\s*\};' -- '*.c' | wc -l
> 776
>
> Refer to the c standard section on initialization 6.7.8 subsections 19 and 21
>
> 19
>
> The initialization shall occur in initializer list order, each initializer provided for a
> particular subobject overriding any previously listed initializer for the same subobject
> all subobjects that are not initialized explicitly shall be initialized implicitly the same as
> objects that have static storage duration.
>
> ...
>
> 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.
>
Joe,

Thanks for providing these sections for c reference !

I will update the commit log and replace { 0 } with { }

Tom