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Message-ID: <20260217113509.GA12624@wp.pl>
Date: Tue, 17 Feb 2026 12:35:09 +0100
From: Stanislaw Gruszka <stf_xl@...pl>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Johannes Berg <johannes@...solutions.net>,
linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v4][next] wifi: iwlegacy: Avoid multiple
-Wflex-array-member-not-at-end warnings
On Mon, Feb 16, 2026 at 06:25:14PM +0900, 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.
>
> Move the conflicting declarations (which in a couple of cases happen
> to be in a union, so the entire unions are moved) to the end of the
> corresponding structures, struct il_frame, and struct il3945_frame.
>
> Notice that `struct il_tx_beacon_cmd`, `struct il4965_tx_resp`, and
> `struct il3945_tx_beacon_cmd` are flexible structures, this is
> structures that contain a flexible-array member.
>
> The case for struct il4965_beacon_notif is different. Since this
> structure is defined by hardware, we create the new `struct
> il4965_tx_resp_hdr` type. We then use this newly created type to
> replace the object type causing trouble in struct il4965_beacon_notif,
> namely `struct il4965_tx_resp`.
>
> Also, once -fms-extensions is enabled, we can use transparent struct
> members in struct il4965_tx_resp.
>
> Notice that the newly created type does not contain the flex-array
> member `agg_status`, which is the object causing the -Wfamnae warnings.
> This object is currently in a union along with `__le32 status`, so
> anything using struct il4965_beacon_notif needs to have its own view
> of `status`. To preserve the memory layout, we therefore add member
> `__le32 beacon_tx_status` to struct il4965_beacon_notif.
>
> After these changes, the size of struct il4965_beacon_notif along
> with its member's offsets remain the same, hence the memory layout
> doesn't change:
>
> Before changes:
> struct il4965_beacon_notif {
> struct il4965_tx_resp beacon_notify_hdr; /* 0 24 */
> __le32 low_tsf; /* 24 4 */
> __le32 high_tsf; /* 28 4 */
> __le32 ibss_mgr_status; /* 32 4 */
>
> /* size: 36, cachelines: 1, members: 4 */
> /* last cacheline: 36 bytes */
> };
>
> After changes:
> struct il4965_beacon_notif {
> struct il4965_tx_resp_hdr beacon_notify_hdr; /* 0 20 */
> __le32 beacon_tx_status; /* 20 4 */
> __le32 low_tsf; /* 24 4 */
> __le32 high_tsf; /* 28 4 */
> __le32 ibss_mgr_status; /* 32 4 */
>
> /* size: 36, cachelines: 1, members: 5 */
> /* last cacheline: 36 bytes */
> };
>
> Lastly, adjust the rest of the code, accordingly.
>
> With these changes fix the following warnings:
>
> 11 drivers/net/wireless/intel/iwlegacy/common.h:526:11: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 11 drivers/net/wireless/intel/iwlegacy/commands.h:2667:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 4 drivers/net/wireless/intel/iwlegacy/3945.h:131:11: 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@...nel.org>
Acked-by: Stanislaw Gruszka <stf_xl@...pl>
Regards
Stanislaw
> ---
> Changes in v4:
> - (Aggh...) Fix a couple of typos in changelog text:
> s/stryct/struct
> s/il4965_beacon_notif/il4965_tx_resp.
>
> Changes in v3:
> - Create new separate struct il4965_tx_resp_hdr, and use
> transparent struct members instead of __struct_group(). (Kees)
> - Update subject line - Add 'wifi:' prefix. (Stanislaw)
> - Link: https://lore.kernel.org/linux-hardening/aZLgfO6z1Gt8aiyc@kspp/
>
> Changes in v2:
> - Use the struct_group() helper, and update the conflicting type
> (struct il4965_tx_resp -> struct il4965_tx_resp_hdr) in
> struct il4965_beacon_notif.
> - Link: https://lore.kernel.org/linux-hardening/aYlkt2WP2oQ1TgeH@kspp/
>
> v1:
> - Link: https://lore.kernel.org/linux-hardening/aR2CtqZI3atH0HmE@kspp/
>
> drivers/net/wireless/intel/iwlegacy/3945.h | 4 +++-
> drivers/net/wireless/intel/iwlegacy/4965-mac.c | 2 +-
> drivers/net/wireless/intel/iwlegacy/commands.h | 9 +++++++--
> drivers/net/wireless/intel/iwlegacy/common.h | 4 +++-
> 4 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/wireless/intel/iwlegacy/3945.h b/drivers/net/wireless/intel/iwlegacy/3945.h
> index fb1e33c89d0e..ed63b31fee9a 100644
> --- a/drivers/net/wireless/intel/iwlegacy/3945.h
> +++ b/drivers/net/wireless/intel/iwlegacy/3945.h
> @@ -123,13 +123,15 @@ enum il3945_antenna {
> #define IEEE80211_FRAME_LEN (IEEE80211_DATA_LEN + IEEE80211_HLEN)
>
> struct il3945_frame {
> + struct list_head list;
> +
> + /* Must be last as it ends in a flexible-array member. */
> union {
> struct ieee80211_hdr frame;
> struct il3945_tx_beacon_cmd beacon;
> u8 raw[IEEE80211_FRAME_LEN];
> u8 cmd[360];
> } u;
> - struct list_head list;
> };
>
> #define SUP_RATE_11A_MAX_NUM_CHANNELS 8
> diff --git a/drivers/net/wireless/intel/iwlegacy/4965-mac.c b/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> index 57fa866efd9f..f5a99a2ee95a 100644
> --- a/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> +++ b/drivers/net/wireless/intel/iwlegacy/4965-mac.c
> @@ -4076,7 +4076,7 @@ il4965_hdl_beacon(struct il_priv *il, struct il_rx_buf *rxb)
> u8 rate = il4965_hw_get_rate(beacon->beacon_notify_hdr.rate_n_flags);
>
> D_RX("beacon status %x retries %d iss %d tsf:0x%.8x%.8x rate %d\n",
> - le32_to_cpu(beacon->beacon_notify_hdr.u.status) & TX_STATUS_MSK,
> + le32_to_cpu(beacon->beacon_tx_status) & TX_STATUS_MSK,
> beacon->beacon_notify_hdr.failure_frame,
> le32_to_cpu(beacon->ibss_mgr_status),
> le32_to_cpu(beacon->high_tsf), le32_to_cpu(beacon->low_tsf), rate);
> diff --git a/drivers/net/wireless/intel/iwlegacy/commands.h b/drivers/net/wireless/intel/iwlegacy/commands.h
> index b61b8f377702..7aba84ac88a1 100644
> --- a/drivers/net/wireless/intel/iwlegacy/commands.h
> +++ b/drivers/net/wireless/intel/iwlegacy/commands.h
> @@ -1690,7 +1690,7 @@ struct agg_tx_status {
> __le16 sequence;
> } __packed;
>
> -struct il4965_tx_resp {
> +struct il4965_tx_resp_hdr {
> u8 frame_count; /* 1 no aggregation, >1 aggregation */
> u8 bt_kill_count; /* # blocked by bluetooth (unused for agg) */
> u8 failure_rts; /* # failures due to unsuccessful RTS */
> @@ -1707,6 +1707,10 @@ struct il4965_tx_resp {
> __le16 reserved;
> __le32 pa_power1; /* RF power amplifier measurement (not used) */
> __le32 pa_power2;
> +} __packed;
> +
> +struct il4965_tx_resp {
> + struct il4965_tx_resp_hdr;
>
> /*
> * For non-agg: frame status TX_STATUS_*
> @@ -2664,7 +2668,8 @@ struct il3945_beacon_notif {
> } __packed;
>
> struct il4965_beacon_notif {
> - struct il4965_tx_resp beacon_notify_hdr;
> + struct il4965_tx_resp_hdr beacon_notify_hdr;
> + __le32 beacon_tx_status;
> __le32 low_tsf;
> __le32 high_tsf;
> __le32 ibss_mgr_status;
> diff --git a/drivers/net/wireless/intel/iwlegacy/common.h b/drivers/net/wireless/intel/iwlegacy/common.h
> index 4c9836ab11dd..21f1c7702add 100644
> --- a/drivers/net/wireless/intel/iwlegacy/common.h
> +++ b/drivers/net/wireless/intel/iwlegacy/common.h
> @@ -518,13 +518,15 @@ struct il_channel_info {
> #define IEEE80211_FRAME_LEN (IEEE80211_DATA_LEN + IEEE80211_HLEN)
>
> struct il_frame {
> + struct list_head list;
> +
> + /* Must be last as it ends in a flexible-array member. */
> union {
> struct ieee80211_hdr frame;
> struct il_tx_beacon_cmd beacon;
> u8 raw[IEEE80211_FRAME_LEN];
> u8 cmd[360];
> } u;
> - struct list_head list;
> };
>
> enum {
> --
> 2.43.0
>
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