wifi: radiotap: Avoid -Wflex-array-member-not-at-end warnings

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

So, in order to avoid ending up with a flexible-array member in the
middle of multiple other structs, we use the `__struct_group()`
helper to create a new tagged `struct ieee80211_radiotap_header_fixed`.
This structure groups together all the members of the flexible
`struct ieee80211_radiotap_header` except the flexible array.

As a result, the array is effectively separated from the rest of the
members without modifying the memory layout of the flexible structure.
We then change the type of the middle struct members currently causing
trouble from `struct ieee80211_radiotap_header` to `struct
ieee80211_radiotap_header_fixed`.

We also want to ensure that in case new members need to be added to the
flexible structure, they are always included within the newly created
tagged struct. For this, we use `static_assert()`. This ensures that the
memory layout for both the flexible structure and the new tagged struct
is the same after any changes.

This approach avoids having to implement `struct ieee80211_radiotap_header_fixed`
as a completely separate structure, thus preventing having to maintain
two independent but basically identical structures, closing the door
to potential bugs in the future.

So, with these changes, fix the following warnings:
drivers/net/wireless/ath/wil6210/txrx.c:309:50: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/ipw2x00/ipw2100.c:2521:50: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/ipw2x00/ipw2200.h:1146:42: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/intel/ipw2x00/libipw.h:595:36: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/marvell/libertas/radiotap.h:34:42: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/marvell/libertas/radiotap.h:5:42: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/microchip/wilc1000/mon.c:10:42: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/microchip/wilc1000/mon.c:15:42: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/virtual/mac80211_hwsim.c:758:42: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/net/wireless/virtual/mac80211_hwsim.c:767:42: 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 <[email protected]>
Link: https://patch.msgid.link/ZwBMtBZKcrzwU7l4@kspp
Signed-off-by: Johannes Berg <[email protected]>

Author: GustavoARSilva

drivers/net/wireless/ath/wil6210/txrx.c

@@ -306,7 +306,7 @@ static void wil_rx_add_radiotap_header(struct wil6210_priv *wil,
 				       struct sk_buff *skb)
 {
 	struct wil6210_rtap {
-		struct ieee80211_radiotap_header rthdr;
+		struct ieee80211_radiotap_header_fixed rthdr;
 		/* fields should be in the order of bits in rthdr.it_present */
 		/* flags */
 		u8 flags;

drivers/net/wireless/intel/ipw2x00/ipw2100.c

@@ -2518,7 +2518,7 @@ static void isr_rx_monitor(struct ipw2100_priv *priv, int i,
 	 * to build this manually element by element, we can write it much
 	 * more efficiently than we can parse it. ORDER MATTERS HERE */
 	struct ipw_rt_hdr {
-		struct ieee80211_radiotap_header rt_hdr;
+		struct ieee80211_radiotap_header_fixed rt_hdr;
 		s8 rt_dbmsignal; /* signal in dbM, kluged to signed */
 	} *ipw_rt;
 

drivers/net/wireless/intel/ipw2x00/ipw2200.h

@@ -1143,7 +1143,7 @@ struct ipw_prom_priv {
  * structure is provided regardless of any bits unset.
  */
 struct ipw_rt_hdr {
-	struct ieee80211_radiotap_header rt_hdr;
+	struct ieee80211_radiotap_header_fixed rt_hdr;
 	u64 rt_tsf;      /* TSF */	/* XXX */
 	u8 rt_flags;	/* radiotap packet flags */
 	u8 rt_rate;	/* rate in 500kb/s */

drivers/net/wireless/marvell/libertas/radiotap.h

@@ -2,7 +2,7 @@
 #include <net/ieee80211_radiotap.h>
 
 struct tx_radiotap_hdr {
-	struct ieee80211_radiotap_header hdr;
+	struct ieee80211_radiotap_header_fixed hdr;
 	u8 rate;
 	u8 txpower;
 	u8 rts_retries;
@@ -31,7 +31,7 @@ struct tx_radiotap_hdr {
 #define IEEE80211_FC_DSTODS          0x0300
 
 struct rx_radiotap_hdr {
-	struct ieee80211_radiotap_header hdr;
+	struct ieee80211_radiotap_header_fixed hdr;
 	u8 flags;
 	u8 rate;
 	u8 antsignal;

drivers/net/wireless/microchip/wilc1000/mon.c

@@ -7,12 +7,12 @@
 #include "cfg80211.h"
 
 struct wilc_wfi_radiotap_hdr {
-	struct ieee80211_radiotap_header hdr;
+	struct ieee80211_radiotap_header_fixed hdr;
 	u8 rate;
 } __packed;
 
 struct wilc_wfi_radiotap_cb_hdr {
-	struct ieee80211_radiotap_header hdr;
+	struct ieee80211_radiotap_header_fixed hdr;
 	u8 rate;
 	u8 dump;
 	u16 tx_flags;

drivers/net/wireless/virtual/mac80211_hwsim.c

@@ -763,7 +763,7 @@ static const struct rhashtable_params hwsim_rht_params = {
 };
 
 struct hwsim_radiotap_hdr {
-	struct ieee80211_radiotap_header hdr;
+	struct ieee80211_radiotap_header_fixed hdr;
 	__le64 rt_tsft;
 	u8 rt_flags;
 	u8 rt_rate;
@@ -772,7 +772,7 @@ struct hwsim_radiotap_hdr {
 } __packed;
 
 struct hwsim_radiotap_ack_hdr {
-	struct ieee80211_radiotap_header hdr;
+	struct ieee80211_radiotap_header_fixed hdr;
 	u8 rt_flags;
 	u8 pad;
 	__le16 rt_channel;

include/net/ieee80211_radiotap.h

@@ -24,32 +24,37 @@
  * struct ieee80211_radiotap_header - base radiotap header
  */
 struct ieee80211_radiotap_header {
-	/**
-	 * @it_version: radiotap version, always 0
-	 */
-	uint8_t it_version;
-
-	/**
-	 * @it_pad: padding (or alignment)
-	 */
-	uint8_t it_pad;
-
-	/**
-	 * @it_len: overall radiotap header length
-	 */
-	__le16 it_len;
-
-	/**
-	 * @it_present: (first) present word
-	 */
-	__le32 it_present;
+	__struct_group(ieee80211_radiotap_header_fixed, hdr, __packed,
+		/**
+		 * @it_version: radiotap version, always 0
+		 */
+		uint8_t it_version;
+
+		/**
+		 * @it_pad: padding (or alignment)
+		 */
+		uint8_t it_pad;
+
+		/**
+		 * @it_len: overall radiotap header length
+		 */
+		__le16 it_len;
+
+		/**
+		 * @it_present: (first) present word
+		 */
+		__le32 it_present;
+	);
 
 	/**
 	 * @it_optional: all remaining presence bitmaps
 	 */
 	__le32 it_optional[];
 } __packed;
 
+static_assert(offsetof(struct ieee80211_radiotap_header, it_optional) == sizeof(struct ieee80211_radiotap_header_fixed),
+	      "struct member likely outside of __struct_group()");
+
 /* version is always 0 */
 #define PKTHDR_RADIOTAP_VERSION	0