netdev - Re: [PATCH][next] zd1211rw/zd_usb.h: Replace zero-length array with flexible-array member

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Message-ID: <c2aa4d8d-1c39-1903-2b49-382f2143e181@embeddedor.com>
Date:   Tue, 10 Mar 2020 17:21:52 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Joe Perches <joe@...ches.com>,
        Jes Sorensen <jes.sorensen@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>
Cc:     Daniel Drake <dsd@...too.org>, Ulrich Kunitz <kune@...ne-taler.de>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] zd1211rw/zd_usb.h: Replace zero-length array with
 flexible-array member



On 3/10/20 5:15 PM, Joe Perches wrote:
> On Tue, 2020-03-10 at 17:13 -0500, Gustavo A. R. Silva wrote:
>>
>> On 3/10/20 5:07 PM, Jes Sorensen wrote:
>>> On 3/10/20 5:52 PM, Gustavo A. R. Silva wrote:
>>>>
>>>> On 3/10/20 8:56 AM, Kalle Valo wrote:
>>>>> + jes
>>>>>
>>>>> "Gustavo A. R. Silva" <gustavo@...eddedor.com> writes:
>>>>>>> I wrote in a confusing way, my question above was about the actual patch
>>>>>>> and not the the title. For example, Jes didn't like this style change:
>>>>>>>
>>>>>>> https://patchwork.kernel.org/patch/11402315/
>>>>>>>
>>>>>>
>>>>>> It doesn't seem that that comment adds a lot to the conversation. The only
>>>>>> thing that it says is literally "fix the compiler". By the way, more than
>>>>>> a hundred patches have already been applied to linux-next[1] and he seems
>>>>>> to be the only person that has commented such a thing.
>>>>>
>>>>> But I also asked who prefers this format in that thread, you should not
>>>>> ignore questions from two maintainers (me and Jes).
>>>>>
>>>>
>>>> I'm sorry. I thought the changelog text had already the proper information.
>>>> In the changelog text I'm quoting the GCC documentation below:
>>>>
>>>> "The preferred mechanism to declare variable-length types like struct line
>>>> above is the ISO C99 flexible array member..." [1]
>>>>
>>>> I'm also including a link to the following KSPP open issue:
>>>>
>>>> https://github.com/KSPP/linux/issues/21
>>>>
>>>> The issue above mentions the following:
>>>>
>>>> "Both cases (0-byte and 1-byte arrays) pose confusion for things like sizeof(),
>>>> CONFIG_FORTIFY_SOURCE."
>>>>
>>>> sizeof(flexible-array-member) triggers a warning because flexible array members have
>>>> incomplete type[1]. There are some instances of code in which the sizeof operator
>>>> is being incorrectly/erroneously applied to zero-length arrays and the result is zero.
>>>> Such instances may be hiding some bugs. So, the idea is also to get completely rid
>>>> of those sorts of issues.
>>>
>>> As I stated in my previous answer, this seems more code churn than an
>>> actual fix. If this is a real problem, shouldn't the work be put into
>>> fixing the compiler to handle foo[0] instead? It seems that is where the
>>> real value would be.
>>>
>>
>> Yeah. But, unfortunately, I'm not a compiler guy, so I'm not able to fix the
>> compiler as you suggest. And I honestly don't see what is so annoying/disturbing
>> about applying a patch that removes the 0 from foo[0] when it brings benefit
>> to the whole codebase.
> 
> As far as I can tell, it doesn't actually make a difference as
> all the compilers produce the same object code with either form.
> 

That's precisely why we can implement these changes, cleanly(the fact
that the compiler produces the same object code). So, the resulting
object code is not the point here.

--
Gustavo