From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member
Date: Thu, 13 Feb 2020 00:13:41 -0600 [thread overview]
Message-ID: <0dd75019-4d02-24ee-fdf1-f713a99d4141@embeddedor.com> (raw)
In-Reply-To: <CANiq72nt19x2Z6ErT8a1_2c0sKfjkv_yUFMZS2mf3HWp3RvnDQ@mail.gmail.com>
Hi Miguel,
On 2/12/20 14:49, Miguel Ojeda wrote:
> Hi Gustavo,
>
> On Wed, Feb 12, 2020 at 8:49 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
>> inadvertenly introduced[3] to the codebase from now on.
>
> s:inadvertenly:inadvertently:
>
Thanks for this.
>> 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>
>
> I saw the discussion regarding this -- thanks! Do you want me to
> handle this or will you push everything centrally? If the latter, have
> my
>
Please, go ahead and handle it.
> Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
>
Thanks
--
Gustavo
next prev parent reply other threads:[~2020-02-13 6:11 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-12 19:52 [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-12 20:49 ` Miguel Ojeda
2020-02-13 6:13 ` Gustavo A. R. Silva [this message]
2020-03-06 21:24 ` Miguel Ojeda
2020-03-07 7:23 ` Gustavo A. R. Silva
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