From: Linus Walleij <linus.walleij@linaro.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] pinctrl: uniphier: Replace zero-length array with flexible-array member
Date: Fri, 21 Feb 2020 15:37:07 +0100 [thread overview]
Message-ID: <CACRpkdaJHQoZZCK0tJVb5Ntxsg+gr1FcHwtdxjQEHo=ZiKkxAQ@mail.gmail.com> (raw)
In-Reply-To: <20200217185437.GA20901@embeddedor>
On Mon, Feb 17, 2020 at 7:51 PM 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>
Patch applied with Masahiro's ACK.
Yours,
Linus Walleij
prev parent reply other threads:[~2020-02-21 14:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-17 18:54 [PATCH] pinctrl: uniphier: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-18 1:24 ` Masahiro Yamada
2020-02-21 14:37 ` Linus Walleij [this message]
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