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

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Date:   Tue, 10 Mar 2020 18:34:31 -0400
From:   Jes Sorensen <jes.sorensen@...il.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.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 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.

Jes