[PATCH] hwmon: (ibmaem) Replace zero-length array with flexible-array member

[PATCH] hwmon: (ibmaem) 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/hwmon/ibmaem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/ibmaem.c b/drivers/hwmon/ibmaem.c
index db63c1295cb2..fb052c2d9c34 100644
--- a/drivers/hwmon/ibmaem.c
+++ b/drivers/hwmon/ibmaem.c
@@ -232,7 +232,7 @@ struct aem_read_sensor_req {
 
 struct aem_read_sensor_resp {
 	struct aem_iana_id	id;
-	u8			bytes[0];
+	u8			bytes[];
 } __packed;
 
 /* Data structures to talk to the IPMI layer */
-- 
2.25.0

Re: [PATCH] hwmon: (ibmaem) Replace zero-length array with flexible-array member

[Guenter Roeck]

On Tue, Feb 11, 2020 at 05:42:37PM -0600, 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
> 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>

Applied to hwmon-next.

Thanks,
Guenter

> ---
>  drivers/hwmon/ibmaem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/ibmaem.c b/drivers/hwmon/ibmaem.c
> index db63c1295cb2..fb052c2d9c34 100644
> --- a/drivers/hwmon/ibmaem.c
> +++ b/drivers/hwmon/ibmaem.c
> @@ -232,7 +232,7 @@ struct aem_read_sensor_req {
>  
>  struct aem_read_sensor_resp {
>  	struct aem_iana_id	id;
> -	u8			bytes[0];
> +	u8			bytes[];
>  } __packed;
>  
>  /* Data structures to talk to the IPMI layer */