Re: [PATCH][next] brcmfmac: Replace zero-length array with flexible-array member

From: Kalle Valo <kvalo@codeaurora.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Arend van Spriel <arend.vanspriel@broadcom.com>,
	Franky Lin <franky.lin@broadcom.com>,
	Hante Meuleman <hante.meuleman@broadcom.com>,
	Chi-Hsien Lin <chi-hsien.lin@cypress.com>,
	Wright Feng <wright.feng@cypress.com>,
	"David S. Miller" <davem@davemloft.net>,
	linux-wireless@vger.kernel.org,
	brcm80211-dev-list.pdl@broadcom.com,
	brcm80211-dev-list@cypress.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	"Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: Re: [PATCH][next] brcmfmac: Replace zero-length array with flexible-array member
Date: Mon, 23 Mar 2020 17:12:42 +0000 (UTC)	[thread overview]
Message-ID: <20200323171242.5E029C432C2@smtp.codeaurora.org> (raw)
In-Reply-To: <20200225020804.GA9428@embeddedor>

"Gustavo A. R. Silva" <gustavo@embeddedor.com> 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
> inadvertently introduced[3] to the codebase from now on.
> 
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
> 
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
> 
> This issue was found with the help of Coccinelle.
> 
> [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")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>

Patch applied to wireless-drivers-next.git, thanks.

232c897eb5ca brcmfmac: Replace zero-length array with flexible-array member

-- 
https://patchwork.kernel.org/patch/11402413/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches