From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Andreas Noever <andreas.noever@gmail.com>,
Michael Jamet <michael.jamet@intel.com>,
Yehezkel Bernat <YehezkelShB@gmail.com>,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] thunderbolt: Replace zero-length array with flexible-array
Date: Mon, 11 May 2020 13:34:15 +0300 [thread overview]
Message-ID: <20200511103415.GG487496@lahna.fi.intel.com> (raw)
In-Reply-To: <20200507192524.GA16580@embeddedor>
On Thu, May 07, 2020 at 02:25:24PM -0500, Gustavo A. R. Silva 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>
Applied, thanks!
next prev parent reply other threads:[~2020-05-11 10:34 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-07 19:25 [PATCH] thunderbolt: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-11 10:34 ` Mika Westerberg [this message]
2020-05-12 18:12 ` Gustavo A. R. Silva
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