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

[ Upstream commit 57be3d3562ca4aa62b8047bc681028cc402af8ce ]

-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 <gustavoars@kernel.org>
Link: https://patch.msgid.link/ZwBMtBZKcrzwU7l4@kspp
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 24 insertions, 19 deletions

diff --git a/include/net/ieee80211_radiotap.h b/include/net/ieee80211_radiotap.h
index 2338f8d2a8b3..c6cb6f642742 100644
--- a/include/net/ieee80211_radiotap.h
+++ b/include/net/ieee80211_radiotap.h
@@ -24,25 +24,27 @@
  * 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
@@ -50,6 +52,9 @@ struct ieee80211_radiotap_header {
 	__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