linux-kernel - Re: [PATCH] usbip: Use fallthrough pseudo-keyword

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Date:   Wed, 8 Jul 2020 08:42:26 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Julia Lawall <julia.lawall@...ia.fr>, Joe Perches <joe@...ches.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] usbip: Use fallthrough pseudo-keyword

On 7/8/20 4:16 AM, Julia Lawall wrote:
> 
> 
> On Tue, 7 Jul 2020, Joe Perches wrote:
> 
>> On Tue, 2020-07-07 at 14:06 -0600, Shuah Khan wrote:
>>> On 7/7/20 1:52 PM, Gustavo A. R. Silva wrote:
>>>> Replace the existing /* fall through */ comments and its variants with
>>>> the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
>>>> fall-through markings when it is the case.
>>>>
>>>> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through
>>>>
>>>
>>> Is fallthrough syntax supported on our min gcc version?
>>
>> No.  Introduced in gcc 7.
>>
>>> Does checkpatch or coccicheck catch these cases?
>>
>> Kinda.  checkpatch isn't very good at it.
>> I _believe_, though I'm not at all sure,
>> that coccinelle can find these.
> 
> I would not guarantee anything about the support of Coccinelle for switch.
> Coccinelle does now have the ability to match on comments.  So since there
> is a distinct comment that it is to be removed, it might be possible to do
> that part automatically.
> 
> Maybe it would have to look something like this:
> 
> @r1@
> comments c : script:python() { code to recognize the comment };
> statement S;
> @@
> 
> S@c
> + fallthrough(); //or whatever is wanted
> 
> @@
> statement r1.S;
> @@
> 
> - S
> - fallthrough();
> + S
> + fallthrough();
> 
> The second rule probably looks pretty strange, but the goal is to remove
> the comments between S and fallthrough();
> 
> There is an example demos/comments.cocci that shows how to access the
> comment information using both ocaml and python.
> 

Thanks Julia. Maybe this is a way to address all of the cases. I am a
bit concerned about min gcc which is 4.8 and the fallthrough syntax
support is in gcc 7

-- Shuah