linux-kernel - Re: [PATCH] treewide: Replace zero-length arrays with flexible-array member

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Date:   Tue, 11 Feb 2020 13:20:36 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] treewide: Replace zero-length arrays with flexible-array
 member



On 2/11/20 12:32, Greg KH wrote:
> On Tue, Feb 11, 2020 at 11:41:26AM -0600, Gustavo A. R. Silva wrote:
>> The current codebase makes use of the zero-length array language
>> extension to the C90 standard, but the preferred mechanism to declare
>> variable-length types such as these ones is a flexible array member[1][2],
>> introduced in C99:
>>
>> struct foo {
>>         int stuff;
>>         struct boo array[];
>> };
>>
>> By making use of the mechanism above, we will get a compiler warning
>> in case the flexible array does not occur last in the structure, which
>> will help us prevent some kind of undefined behavior bugs from being
>> unadvertenly introduced[3] to the codebase from now on.
>>
>> All these instances of code were found with the help of the following
>> Coccinelle script:
>>
>> @@
>> identifier S, member, array;
>> type T1, T2;
>> @@
>>
>> struct S {
>>   ...
>>   T1 member;
>>   T2 array[
>> - 0
>>   ];
>> };
>>
>> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
>> [2] https://github.com/KSPP/linux/issues/21
>> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>>
>> NOTE: I'll carry this in my -next tree for the v5.6 merge window.
> 
> Why not carve this up into per-subsystem patches so that we can apply
> them to our 5.7-rc1 trees and then you submit the "remaining" that don't
> somehow get merged at that timeframe for 5.7-rc2?
> 

Yep, sounds good. I'll do that.

Thanks
--
Gustavo