From: Kalle Valo <kvalo@codeaurora.org>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Igor Mitsyanko <imitsyanko@quantenna.com>,
Avinash Patil <avinashp@quantenna.com>,
Sergey Matyukevich <smatyukevich@quantenna.com>,
linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] qtnfmac: Replace zero-length array with flexible-array
Date: Tue, 12 May 2020 08:56:47 +0000 (UTC) [thread overview]
Message-ID: <20200512085647.85C80C433F2@smtp.codeaurora.org> (raw)
In-Reply-To: <20200507191926.GA15970@embeddedor>
"Gustavo A. R. Silva" <gustavoars@kernel.org> 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]
>
> sizeof(flexible-array-member) triggers a warning because flexible array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be hiding
> some bugs. So, this work (flexible-array member conversions) will also
> help to get completely rid of those sorts of issues.
>
> 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 <gustavoars@kernel.org>
> Reviewed-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Patch applied to wireless-drivers-next.git, thanks.
55bb8a2b01a3 qtnfmac: Replace zero-length array with flexible-array
--
https://patchwork.kernel.org/patch/11534767/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
prev parent reply other threads:[~2020-05-12 8:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-07 19:19 [PATCH] qtnfmac: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-08 17:15 ` Sergey Matyukevich
2020-05-12 8:56 ` Kalle Valo [this message]
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