linux-kernel - [PATCH v2] mac80211: Add attribute aligned(2) to struct 'action'

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Date:   Thu, 24 Jan 2019 19:19:57 +0100
From:   Mathieu Malaterre <malat@...ian.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Mathieu Malaterre <malat@...ian.org>,
        Johannes Berg <johannes.berg@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] mac80211: Add attribute aligned(2) to struct 'action'

During refactor in commit 9e478066eae4 ("mac80211: fix MU-MIMO
follow-MAC mode") a new struct 'action' was declared with packed
attribute as:

  struct {
          struct ieee80211_hdr_3addr hdr;
          u8 category;
          u8 action_code;
  } __packed action;

But since struct 'ieee80211_hdr_3addr' is declared with an aligned
keyword as:

  struct ieee80211_hdr {
  	__le16 frame_control;
  	__le16 duration_id;
  	u8 addr1[ETH_ALEN];
  	u8 addr2[ETH_ALEN];
  	u8 addr3[ETH_ALEN];
  	__le16 seq_ctrl;
  	u8 addr4[ETH_ALEN];
  } __packed __aligned(2);

Solve the ambiguity of placing aligned structure in a packed one by
adding the aligned(2) attribute to struct 'action'. This seems to be the
behavior of gcc anyway, since the following is still compiling:

  BUILD_BUG_ON(sizeof(action) != IEEE80211_MIN_ACTION_SIZE + 1);

This removes the following warning (W=1):

  net/mac80211/rx.c:234:2: warning: alignment 1 of 'struct <anonymous>' is less than 2 [-Wpacked-not-aligned]

Cc: Johannes Berg <johannes.berg@...el.com>
Suggested-by: Johannes Berg <johannes@...solutions.net>
Signed-off-by: Mathieu Malaterre <malat@...ian.org>
---
v2: It was suggested by Johannes that an arch actually need the pack attribute (alpha).

 net/mac80211/rx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 45aad3d3108c..885df250b67e 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -231,7 +231,7 @@ static void ieee80211_handle_mu_mimo_mon(struct ieee80211_sub_if_data *sdata,
 		struct ieee80211_hdr_3addr hdr;
 		u8 category;
 		u8 action_code;
-	} __packed action;
+	} __packed __aligned(2) action;
 
 	if (!sdata)
 		return;
-- 
2.19.2