Re: [PATCH][next] Bluetooth: hci.h: Avoid a couple -Wflex-array-member-not-at-end warnings

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

Hi all,

Friendly ping: who can take this, please?

Thanks
-Gustavo

On 2/24/26 00:31, 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 hci_std_codecs and struct hci_std_codecs_v2 are flexible
> structures, this is structures that contain a flexible-array member
> (__u8 codec[]; and struct hci_std_codec_v2 codec[];, correspondingly.)
> 
> Since struct hci_rp_read_local_supported_codecs and struct
> hci_rp_read_local_supported_codecs_v2 are defined by hardware, we
> create the new struct hci_std_codecs_hdr and struct hci_std_codecs_v2_hdr
> types, and use them to replace the object types causing trouble in
> struct hci_rp_read_local_supported_codecs and struct
> hci_rp_read_local_supported_codecs_v2, namely struct hci_std_codecs
> std_codecs; and struct hci_std_codecs_v2_hdr std_codecs;.
> 
> Also, once -fms-extensions is enabled, we can use transparent struct
> members in both struct hci_std_codecs and struct hci_std_codecs_v2_hdr.
> 
> Notice that the newly created types does not contain the flex-array
> member `codec`, which is the object causing the -Wfamnae warnings.
> 
> After these changes, the size of struct hci_rp_read_local_supported_codecs
> and struct hci_rp_read_local_supported_codecs_v2, along with their
> member's offsets remain the same, hence the memory layouts don't
> change:
> 
> Before changes:
> struct hci_rp_read_local_supported_codecs {
>          __u8                       status;               /*     0     1 */
>          struct hci_std_codecs      std_codecs;           /*     1     1 */
>          struct hci_vnd_codecs      vnd_codecs;           /*     2     1 */
> 
>          /* size: 3, cachelines: 1, members: 3 */
>          /* last cacheline: 3 bytes */
> } __attribute__((__packed__));
> 
> struct hci_rp_read_local_supported_codecs_v2 {
>          __u8                       status;               /*     0     1 */
>          struct hci_std_codecs_v2   std_codecs;           /*     1     1 */
>          struct hci_vnd_codecs_v2   vendor_codecs;        /*     2     1 */
> 
>          /* size: 3, cachelines: 1, members: 3 */
>          /* last cacheline: 3 bytes */
> } __attribute__((__packed__));
> 
> After changes:
> struct hci_rp_read_local_supported_codecs {
> 	__u8                       status;               /*     0     1 */
> 	struct hci_std_codecs_hdr  std_codecs;           /*     1     1 */
> 	struct hci_vnd_codecs      vnd_codecs;           /*     2     1 */
> 
> 	/* size: 3, cachelines: 1, members: 3 */
> 	/* last cacheline: 3 bytes */
> } __attribute__((__packed__));
> 
> struct hci_rp_read_local_supported_codecs_v2 {
> 	__u8                       status;               /*     0     1 */
> 	struct hci_std_codecs_v2_hdr std_codecs;         /*     1     1 */
> 	struct hci_vnd_codecs_v2   vendor_codecs;        /*     2     1 */
> 
> 	/* size: 3, cachelines: 1, members: 3 */
> 	/* last cacheline: 3 bytes */
> } __attribute__((__packed__));
> 
> With these changes fix the following warnings:
> 
> include/net/bluetooth/hci.h:1490:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/net/bluetooth/hci.h:1525:34: 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>
> ---
>   include/net/bluetooth/hci.h | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> index 89ad9470fa71..572b1c620c5d 100644
> --- a/include/net/bluetooth/hci.h
> +++ b/include/net/bluetooth/hci.h
> @@ -1468,8 +1468,12 @@ struct hci_rp_read_data_block_size {
>   } __packed;
>   
>   #define HCI_OP_READ_LOCAL_CODECS	0x100b
> -struct hci_std_codecs {
> +struct hci_std_codecs_hdr {
>   	__u8	num;
> +} __packed;
> +
> +struct hci_std_codecs {
> +	struct hci_std_codecs_hdr;
>   	__u8	codec[];
>   } __packed;
>   
> @@ -1487,7 +1491,7 @@ struct hci_vnd_codecs {
>   
>   struct hci_rp_read_local_supported_codecs {
>   	__u8	status;
> -	struct hci_std_codecs std_codecs;
> +	struct hci_std_codecs_hdr std_codecs;
>   	struct hci_vnd_codecs vnd_codecs;
>   } __packed;
>   
> @@ -1504,8 +1508,12 @@ struct hci_std_codec_v2 {
>   	__u8	transport;
>   } __packed;
>   
> -struct hci_std_codecs_v2 {
> +struct hci_std_codecs_v2_hdr {
>   	__u8	num;
> +} __packed;
> +
> +struct hci_std_codecs_v2 {
> +	struct hci_std_codecs_v2_hdr;
>   	struct hci_std_codec_v2 codec[];
>   } __packed;
>   
> @@ -1522,7 +1530,7 @@ struct hci_vnd_codecs_v2 {
>   
>   struct hci_rp_read_local_supported_codecs_v2 {
>   	__u8	status;
> -	struct hci_std_codecs_v2 std_codecs;
> +	struct hci_std_codecs_v2_hdr std_codecs;
>   	struct hci_vnd_codecs_v2 vendor_codecs;
>   } __packed;
>