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

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Message-ID: <541a4f6a-60b3-a171-a223-1692f78b48ee@embeddedor.com>
Date:   Tue, 11 Feb 2020 14:16:19 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        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 13:35, Kees Cook 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.
> 
> Is there a compiler warning we can enable to avoid new 0-byte arrays
> from entering the kernel source tree? I can only find "-pedantic" which
> enables way too many other checks.
> 

Months ago, I only found -pedantic, too. And we definitely don't want
to use it for this. :/

--
Gustavo