[PATCH v2][next] wifi: ath6kl: wmi: Avoid -Wflex-array-member-not-at-end warning

[PATCH v2][next] wifi: ath6kl: wmi: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

struct bss_bias_info is a flexible structure, this is a structure
that contains a flexible-array member (struct bss_bias bss_bias[]).

Since struct roam_ctrl_cmd is defined by hardware, we create the new
struct bss_bias_info_hdr type, and use it to replace the object type
causing trouble in struct roam_ctrl_cmd, namely struct bss_bias_info.

Also, once -fms-extensions is enabled, we can use transparent struct
members in struct bss_bias_info.

Notice that the newly created type does not contain the flex-array
member `bss_bias`, which is the object causing the -Wfamnae warning.

After these changes, the size of struct roam_ctrl_cmd, along
with its member's offsets remain the same, hence the memory layout
doesn't change:

Before changes:
struct roam_ctrl_cmd {
	union {
		u8                 bssid[6];             /*     0     6 */
		u8                 roam_mode;            /*     0     1 */
		struct bss_bias_info bss;            	 /*     0     1 */
		struct low_rssi_scan_params params;      /*     0     8 */
	} info;                                          /*     0     8 */
	u8                         roam_ctrl;            /*     8     1 */

	/* size: 9, cachelines: 1, members: 2 */
	/* last cacheline: 9 bytes */
} __attribute__((__packed__));

After changes:
struct roam_ctrl_cmd {
	union {
		u8                 bssid[6];             /*     0     6 */
		u8                 roam_mode;            /*     0     1 */
		struct bss_bias_info_hdr bss;            /*     0     1 */
		struct low_rssi_scan_params params;      /*     0     8 */
	} info;                                          /*     0     8 */
	u8                         roam_ctrl;            /*     8     1 */

	/* size: 9, cachelines: 1, members: 2 */
	/* last cacheline: 9 bytes */
} __attribute__((__packed__));

With these changes fix the following warning:

drivers/net/wireless/ath/ath6kl/wmi.h:1658:20: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v2:
 - Create new separate struct bss_bias_info_hdr, and use
   transparent struct members (in struct bss_bias_info)
   instead of rearranging members in struct roam_ctrl_cmd.
 - Update subject line - Add 'wifi:' prefix.

v1:
 - Link: https://lore.kernel.org/linux-hardening/aR153k4ExCD-QTMq@kspp/

 drivers/net/wireless/ath/ath6kl/wmi.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/ath/ath6kl/wmi.h b/drivers/net/wireless/ath/ath6kl/wmi.h
index 3080d82e25cc..d2a5c96fc878 100644
--- a/drivers/net/wireless/ath/ath6kl/wmi.h
+++ b/drivers/net/wireless/ath/ath6kl/wmi.h
@@ -1635,8 +1635,12 @@ struct bss_bias {
 	s8 bias;
 } __packed;
 
-struct bss_bias_info {
+struct bss_bias_info_hdr {
 	u8 num_bss;
+} __packed;
+
+struct bss_bias_info {
+	struct bss_bias_info_hdr;
 	struct bss_bias bss_bias[];
 } __packed;
 
@@ -1652,7 +1656,7 @@ struct roam_ctrl_cmd {
 	union {
 		u8 bssid[ETH_ALEN]; /* WMI_FORCE_ROAM */
 		u8 roam_mode; /* WMI_SET_ROAM_MODE */
-		struct bss_bias_info bss; /* WMI_SET_HOST_BIAS */
+		struct bss_bias_info_hdr bss; /* WMI_SET_HOST_BIAS */
 		struct low_rssi_scan_params params; /* WMI_SET_LRSSI_SCAN_PARAMS
 						     */
 	} __packed info;
-- 
2.43.0

Re: [PATCH v2][next] wifi: ath6kl: wmi: Avoid -Wflex-array-member-not-at-end warning

[Jeff Johnson]

On 2/16/2026 9:10 PM, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> struct bss_bias_info is a flexible structure, this is a structure
> that contains a flexible-array member (struct bss_bias bss_bias[]).
> 
> Since struct roam_ctrl_cmd is defined by hardware, we create the new
> struct bss_bias_info_hdr type, and use it to replace the object type
> causing trouble in struct roam_ctrl_cmd, namely struct bss_bias_info.
> 
> Also, once -fms-extensions is enabled, we can use transparent struct
> members in struct bss_bias_info.
> 
> Notice that the newly created type does not contain the flex-array
> member `bss_bias`, which is the object causing the -Wfamnae warning.
> 
> After these changes, the size of struct roam_ctrl_cmd, along
> with its member's offsets remain the same, hence the memory layout
> doesn't change:
> 
> Before changes:
> struct roam_ctrl_cmd {
> 	union {
> 		u8                 bssid[6];             /*     0     6 */
> 		u8                 roam_mode;            /*     0     1 */
> 		struct bss_bias_info bss;            	 /*     0     1 */
> 		struct low_rssi_scan_params params;      /*     0     8 */
> 	} info;                                          /*     0     8 */
> 	u8                         roam_ctrl;            /*     8     1 */
> 
> 	/* size: 9, cachelines: 1, members: 2 */
> 	/* last cacheline: 9 bytes */
> } __attribute__((__packed__));
> 
> After changes:
> struct roam_ctrl_cmd {
> 	union {
> 		u8                 bssid[6];             /*     0     6 */
> 		u8                 roam_mode;            /*     0     1 */
> 		struct bss_bias_info_hdr bss;            /*     0     1 */
> 		struct low_rssi_scan_params params;      /*     0     8 */
> 	} info;                                          /*     0     8 */
> 	u8                         roam_ctrl;            /*     8     1 */
> 
> 	/* size: 9, cachelines: 1, members: 2 */
> 	/* last cacheline: 9 bytes */
> } __attribute__((__packed__));
> 
> With these changes fix the following warning:
> 
> drivers/net/wireless/ath/ath6kl/wmi.h:1658:20: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> Changes in v2:
>  - Create new separate struct bss_bias_info_hdr, and use
>    transparent struct members (in struct bss_bias_info)
>    instead of rearranging members in struct roam_ctrl_cmd.
>  - Update subject line - Add 'wifi:' prefix.
> 
> v1:
>  - Link: https://lore.kernel.org/linux-hardening/aR153k4ExCD-QTMq@kspp/
> 
>  drivers/net/wireless/ath/ath6kl/wmi.h | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/ath6kl/wmi.h b/drivers/net/wireless/ath/ath6kl/wmi.h
> index 3080d82e25cc..d2a5c96fc878 100644
> --- a/drivers/net/wireless/ath/ath6kl/wmi.h
> +++ b/drivers/net/wireless/ath/ath6kl/wmi.h
> @@ -1635,8 +1635,12 @@ struct bss_bias {
>  	s8 bias;
>  } __packed;
>  
> -struct bss_bias_info {
> +struct bss_bias_info_hdr {
>  	u8 num_bss;
> +} __packed;
> +
> +struct bss_bias_info {
> +	struct bss_bias_info_hdr;
>  	struct bss_bias bss_bias[];
>  } __packed;
>  
> @@ -1652,7 +1656,7 @@ struct roam_ctrl_cmd {
>  	union {
>  		u8 bssid[ETH_ALEN]; /* WMI_FORCE_ROAM */
>  		u8 roam_mode; /* WMI_SET_ROAM_MODE */
> -		struct bss_bias_info bss; /* WMI_SET_HOST_BIAS */
> +		struct bss_bias_info_hdr bss; /* WMI_SET_HOST_BIAS */
>  		struct low_rssi_scan_params params; /* WMI_SET_LRSSI_SCAN_PARAMS
>  						     */
>  	} __packed info;

That bss member appears to be completely unused
(bssid, roam_mode, and params are used)

So IMO the better solution is to remove bss from the union.
And I think struct bss_bias and struct bss_bias_info can also be removed.

/jeff

Re: [PATCH v2][next] wifi: ath6kl: wmi: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

>> @@ -1652,7 +1656,7 @@ struct roam_ctrl_cmd {
>>   	union {
>>   		u8 bssid[ETH_ALEN]; /* WMI_FORCE_ROAM */
>>   		u8 roam_mode; /* WMI_SET_ROAM_MODE */
>> -		struct bss_bias_info bss; /* WMI_SET_HOST_BIAS */
>> +		struct bss_bias_info_hdr bss; /* WMI_SET_HOST_BIAS */
>>   		struct low_rssi_scan_params params; /* WMI_SET_LRSSI_SCAN_PARAMS
>>   						     */
>>   	} __packed info;
> 
> That bss member appears to be completely unused
> (bssid, roam_mode, and params are used)
> 
> So IMO the better solution is to remove bss from the union.
> And I think struct bss_bias and struct bss_bias_info can also be removed.

Even if they're not used, are you sure they aren't there simply	
to define the memory layout of struct roam_ctrl_cmd?

As Kees commented[1], struct roam_ctrl_cmd appears to be a
hardware interface... See below:

drivers/net/wireless/ath/ath6kl/wmi.c:
  755 /*
  756  * Mechanism to modify the roaming behavior in the firmware. The lower rssi
  757  * at which the station has to roam can be passed with
  758  * WMI_SET_LRSSI_SCAN_PARAMS. Subtract 96 from RSSI to get the signal level
  759  * in dBm.
  760  */
  761 int ath6kl_wmi_set_roam_lrssi_cmd(struct wmi *wmi, u8 lrssi)
  762 {
  763         struct sk_buff *skb;
  764         struct roam_ctrl_cmd *cmd;
  765
  766         skb = ath6kl_wmi_get_new_buf(sizeof(*cmd));
  767         if (!skb)
  768                 return -ENOMEM;
  769
  770         cmd = (struct roam_ctrl_cmd *) skb->data;
...
}

Thanks
-Gustavo

[1] https://lore.kernel.org/linux-hardening/202601151627.99DFE54@keescook/

Re: [PATCH v2][next] wifi: ath6kl: wmi: Avoid -Wflex-array-member-not-at-end warning

[Jeff Johnson]

On 2/18/2026 1:38 AM, Gustavo A. R. Silva wrote:
> 
>>> @@ -1652,7 +1656,7 @@ struct roam_ctrl_cmd {
>>>   	union {
>>>   		u8 bssid[ETH_ALEN]; /* WMI_FORCE_ROAM */
>>>   		u8 roam_mode; /* WMI_SET_ROAM_MODE */
>>> -		struct bss_bias_info bss; /* WMI_SET_HOST_BIAS */
>>> +		struct bss_bias_info_hdr bss; /* WMI_SET_HOST_BIAS */
>>>   		struct low_rssi_scan_params params; /* WMI_SET_LRSSI_SCAN_PARAMS
>>>   						     */
>>>   	} __packed info;
>>
>> That bss member appears to be completely unused
>> (bssid, roam_mode, and params are used)
>>
>> So IMO the better solution is to remove bss from the union.
>> And I think struct bss_bias and struct bss_bias_info can also be removed.
> 
> Even if they're not used, are you sure they aren't there simply	
> to define the memory layout of struct roam_ctrl_cmd?
> 
> As Kees commented[1], struct roam_ctrl_cmd appears to be a
> hardware interface... See below:
> 
> drivers/net/wireless/ath/ath6kl/wmi.c:
>   755 /*
>   756  * Mechanism to modify the roaming behavior in the firmware. The lower rssi
>   757  * at which the station has to roam can be passed with
>   758  * WMI_SET_LRSSI_SCAN_PARAMS. Subtract 96 from RSSI to get the signal level
>   759  * in dBm.
>   760  */
>   761 int ath6kl_wmi_set_roam_lrssi_cmd(struct wmi *wmi, u8 lrssi)
>   762 {
>   763         struct sk_buff *skb;
>   764         struct roam_ctrl_cmd *cmd;
>   765
>   766         skb = ath6kl_wmi_get_new_buf(sizeof(*cmd));
>   767         if (!skb)
>   768                 return -ENOMEM;
>   769
>   770         cmd = (struct roam_ctrl_cmd *) skb->data;
> ...
> }

yes, it defines a hardware interface. But note the 'info' is a union, and each
member of the union is there to support a specific value of roam_ctrl. And
since the WMI_SET_HOST_BIAS roam_ctrl is not used, the only important thing to
consider with your patch is that the location of the roam_ctrl field must not
change, and hence the size of union info must not change.

pahole of the original:
struct roam_ctrl_cmd {
	union {
		u8                 bssid[6];             /*     0     6 */
		u8                 roam_mode;            /*     0     1 */
		struct bss_bias_info bss;                /*     0     1 */
		struct low_rssi_scan_params params;      /*     0     8 */
	} info;                                          /*     0     8 */
	u8                         roam_ctrl;            /*     8     1 */

	/* size: 9, cachelines: 1, members: 2 */
	/* last cacheline: 9 bytes */
} __attribute__((__packed__));

pahole with struct bss removed:
struct roam_ctrl_cmd {
	union {
		u8                 bssid[6];             /*     0     6 */
		u8                 roam_mode;            /*     0     1 */
		struct low_rssi_scan_params params;      /*     0     8 */
	} info;                                          /*     0     8 */
	u8                         roam_ctrl;            /*     8     1 */

	/* size: 9, cachelines: 1, members: 2 */
	/* last cacheline: 9 bytes */
} __attribute__((__packed__));

So the size of the message and the location of roam_ctrl is unchanged.

/jeff

Re: [PATCH v2][next] wifi: ath6kl: wmi: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

[..]

> yes, it defines a hardware interface. But note the 'info' is a union, and each
> member of the union is there to support a specific value of roam_ctrl. And
> since the WMI_SET_HOST_BIAS roam_ctrl is not used, the only important thing to
> consider with your patch is that the location of the roam_ctrl field must not
> change, and hence the size of union info must not change.
> 

[..]

> So the size of the message and the location of roam_ctrl is unchanged.

Perfect! With that confirmation, I can proceed with v3. :)

Thanks!
-Gustavo