linux-kernel - Re: [PATCH][next] zd1211rw/zd_usb.h: Replace zero-length array with flexible-array member

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Message-ID: <87k13yq2jo.fsf@kamboji.qca.qualcomm.com>
Date:   Thu, 05 Mar 2020 16:50:03 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Daniel Drake <dsd@...too.org>, Ulrich Kunitz <kune@...ne-taler.de>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] zd1211rw/zd_usb.h: Replace zero-length array with flexible-array member

"Gustavo A. R. Silva" <gustavo@...eddedor.com> writes:

> 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/net/wireless/zydas/zd1211rw/zd_usb.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)

"zd1211rw: " is enough, no need to have the filename in the title.

But I asked this already in an earlier patch, who prefers this format?
It already got opposition so I'm not sure what to do.

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