linux-kernel - RE: [PATCH] mei: bus: replace zero-length array with flexible-array member

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Date:   Wed, 12 Feb 2020 22:19:48 +0000
From:   "Winkler, Tomas" <tomas.winkler@...el.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Usyskin, Alexander" <alexander.usyskin@...el.com>,
        "Lubart, Vitaly" <vitaly.lubart@...el.com>
Subject: RE: [PATCH] mei: bus: replace zero-length array with flexible-array
 member



> -----Original Message-----
> From: Gustavo A. R. Silva <gustavo@...eddedor.com>
> Sent: Tuesday, February 11, 2020 23:08
> To: Winkler, Tomas <tomas.winkler@...el.com>; Arnd Bergmann
> <arnd@...db.de>; Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: linux-kernel@...r.kernel.org; Gustavo A. R. Silva
> <gustavo@...eddedor.com>
> Subject: [PATCH] mei: bus: replace zero-length array with flexible-array member
> 
> 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.
> 
> 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>
Ack.

> ---
>  drivers/misc/mei/bus-fixup.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/mei/bus-fixup.c b/drivers/misc/mei/bus-fixup.c index
> 5fcac02233af..aa3648d59a8a 100644
> --- a/drivers/misc/mei/bus-fixup.c
> +++ b/drivers/misc/mei/bus-fixup.c
> @@ -107,7 +107,7 @@ struct mkhi_rule_id {  struct mkhi_fwcaps {
>  	struct mkhi_rule_id id;
>  	u8 len;
> -	u8 data[0];
> +	u8 data[];
>  } __packed;
> 
>  struct mkhi_fw_ver_block {
> @@ -135,7 +135,7 @@ struct mkhi_msg_hdr {
> 
>  struct mkhi_msg {
>  	struct mkhi_msg_hdr hdr;
> -	u8 data[0];
> +	u8 data[];
>  } __packed;
> 
>  #define MKHI_OSVER_BUF_LEN (sizeof(struct mkhi_msg_hdr) + \
> --
> 2.25.0