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

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Message-ID: <948ec681-c4ee-3479-8d8b-5aa1e358ec04@embeddedor.com>
Date:   Tue, 10 Mar 2020 17:36:39 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Jes Sorensen <jes.sorensen@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>
Cc:     Joe Perches <joe@...ches.com>, 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, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] zd1211rw/zd_usb.h: Replace zero-length array with
 flexible-array member



On 3/10/20 5:34 PM, Jes Sorensen wrote:
> On 3/10/20 6:31 PM, Gustavo A. R. Silva wrote:
>>
>>
>> On 3/10/20 5:20 PM, Jes Sorensen wrote:
>>> On 3/10/20 6:13 PM, Gustavo A. R. Silva wrote:
>>>>
>>>>
>>>> On 3/10/20 5:07 PM, Jes Sorensen wrote:
>>>>> 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.
>>>
>>> My point is that it adds what seems like unnecessary churn, which is not
>>> a benefit, and it doesn't improve the generated code.
>>>
>>
>> As an example of one of the benefits of this is that the compiler won't trigger
>> a warning in the following case:
>>
>> struct boo {
>> 	int stuff;
>> 	struct foo array[0];
>> 	int morestuff;
>> };
>>
>> The result of the code above is an undefined behavior.
>>
>> On the other hand in the case below, the compiles does trigger a warning:
>>
>> struct boo {
>> 	int stuff;
>> 	struct foo array[];
>> 	int morestuff;
>> };
> 
> Right, this just underlines my prior argument, that this should be fixed
> in the compiler.
> 

In the meantime it's not at all harmful to do something about it in the codebase.

Thanks
--
Gustavo