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

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

[Gustavo A. R. Silva]

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@embeddedor.com>
---
 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

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

[Winkler, Tomas]

> -----Original Message-----
> From: Gustavo A. R. Silva <gustavo@embeddedor.com>
> Sent: Tuesday, February 11, 2020 23:08
> To: Winkler, Tomas <tomas.winkler@intel.com>; Arnd Bergmann
> <arnd@arndb.de>; Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: linux-kernel@vger.kernel.org; Gustavo A. R. Silva
> <gustavo@embeddedor.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@embeddedor.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