[PATCH] mac80211: Remove attribute packed from struct 'action'

[PATCH] mac80211: Remove attribute packed from struct 'action'

[Mathieu Malaterre]

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
removing the packed attribute from struct. 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@intel.com>
Signed-off-by: Mathieu Malaterre <malat@debian.org>
---
 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..709359650149 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;
+	} action;
 
 	if (!sdata)
 		return;
-- 
2.19.2

Re: [PATCH] mac80211: Remove attribute packed from struct 'action'

[Johannes Berg]

On Thu, 2019-01-24 at 19:05 +0100, Mathieu Malaterre wrote:
> 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
> removing the packed attribute from struct. 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);

I'm not sure this will work on all platforms, didn't something like
alpha pad out u8's to u32 when not requiring packing?

I guess I'd feel better about using __packed __aligned(2) here as well,
which should solve the warning too?

johannes

Re: [PATCH] mac80211: Remove attribute packed from struct 'action'

[Mathieu Malaterre]

On Thu, Jan 24, 2019 at 7:08 PM Johannes Berg <johannes@sipsolutions.net> wrote:
>
> On Thu, 2019-01-24 at 19:05 +0100, Mathieu Malaterre wrote:
> > 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
> > removing the packed attribute from struct. 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);
>
> I'm not sure this will work on all platforms, didn't something like
> alpha pad out u8's to u32 when not requiring packing?

I was not aware of that.

> I guess I'd feel better about using __packed __aligned(2) here as well,
> which should solve the warning too?

Indeed, I will re-spin a v2 then.

Re: [PATCH] mac80211: Remove attribute packed from struct 'action'

[Johannes Berg]

On Thu, 2019-01-24 at 19:14 +0100, Mathieu Malaterre wrote:

> > I'm not sure this will work on all platforms, didn't something like
> > alpha pad out u8's to u32 when not requiring packing?
> 
> I was not aware of that.

TBH, I'm not actually sure about that. Pure hearsay. If anyone knows,
I'd like to know too :)

johannes

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

[Mathieu Malaterre]

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@intel.com>
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Mathieu Malaterre <malat@debian.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