linux-kernel - Re: [PATCH] mtd: rawnand: Replace zero-length array with flexible-array member

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Message-ID: <CAK7LNARPK=AgshKO1k0BtdYg5wLUp7e9s3zA2-jGLGO26a+A3A@mail.gmail.com>
Date:   Thu, 27 Feb 2020 19:59:07 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Liang Yang <liang.yang@...ogic.com>,
        Kevin Hilman <khilman@...libre.com>,
        Xiaolei Li <xiaolei.li@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic@...ts.infradead.org,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] mtd: rawnand: Replace zero-length array with
 flexible-array member

On Thu, Feb 27, 2020 at 7:25 AM Gustavo A. R. Silva
<gustavo@...eddedor.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@...eddedor.com>
> ---
>  drivers/mtd/nand/raw/denali.h       | 2 +-


Acked-by: Masahiro Yamada <yamada.masahiro@...ionext.com>


>  drivers/mtd/nand/raw/marvell_nand.c | 2 +-
>  drivers/mtd/nand/raw/meson_nand.c   | 2 +-
>  drivers/mtd/nand/raw/mtk_nand.c     | 2 +-
>  drivers/mtd/nand/raw/nand_hynix.c   | 2 +-
>  drivers/mtd/nand/raw/sunxi_nand.c   | 2 +-
>  6 files changed, 6 insertions(+), 6 deletions(-)
>

-- 
Best Regards
Masahiro Yamada