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

From: Kees Cook <keescook@chromium.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: linux-kernel@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	Greg KH <gregkh@linuxfoundation.org>,
	linux-crypto@vger.kernel.org, netdev@vger.kernel.org,
	linux-usb@vger.kernel.org
Subject: Re: [PATCH] treewide: Replace zero-length arrays with flexible-array member
Date: Tue, 11 Feb 2020 11:35:50 -0800	[thread overview]
Message-ID: <202002111132.4A4F073CAF@keescook> (raw)
In-Reply-To: <20200211174126.GA29960@embeddedor>

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.

-- 
Kees Cook