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Message-ID: <71aa855b-54b8-5fef-0d10-b9f132536af2@collabora.com>
Date: Mon, 23 Mar 2020 15:01:26 +0100
From: Enric Balletbo i Serra <enric.balletbo@...labora.com>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
Benson Leung <bleung@...omium.org>,
Guenter Roeck <groeck@...omium.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] chrome: cros_ec_chardev: Replace zero-length array
with flexible-array member
Hi Gustavo,
On 21/3/20 0:15, 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]
>
> 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>
Queued for 5.7. Thanks!
~ Enric
> ---
> drivers/platform/chrome/cros_ec_chardev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/chrome/cros_ec_chardev.c
> index b51ab24055f3..e0bce869c49a 100644
> --- a/drivers/platform/chrome/cros_ec_chardev.c
> +++ b/drivers/platform/chrome/cros_ec_chardev.c
> @@ -48,7 +48,7 @@ struct ec_event {
> struct list_head node;
> size_t size;
> u8 event_type;
> - u8 data[0];
> + u8 data[];
> };
>
> static int ec_get_version(struct cros_ec_dev *ec, char *str, int maxlen)
>
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