Re: [PATCH] carl9170: fix struct alignment conflict

[Christian Lamparter]

On 04/02/2021 17:29, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> Multiple structures in the carl9170 driver have alignment
> impossible alignment constraints that gcc warns about when
> building with 'make W=1':
>
> drivers/net/wireless/ath/carl9170/fwcmd.h:243:2: warning: alignment 1 of 'union <anonymous>' is less than 4 [-Wpacked-not-aligned]
> drivers/net/wireless/ath/carl9170/wlan.h:373:1: warning: alignment 1 of 'struct ar9170_rx_frame_single' is less than 2 [-Wpacked-not-aligned]
>
> In the carl9170_cmd structure, multiple members that have an explicit
> alignment requirement of four bytes are added into a union with explicit
> byte alignment, but this in turn is part of a structure that also has
> four-byte alignment.
>
> In the wlan.h header, multiple structures contain a ieee80211_hdr member
> that is required to be two-byte aligned to avoid alignmnet faults when
> processing network headers, but all members are forced to be byte-aligned
> using the __packed tag at the end of the struct definition.
>
> In both cases, leaving out the packing does not change the internal
> layout of the structure but changes the alignment constraint of the
> structure itself.
>
> Change all affected structures to only apply packing where it does
> not violate the alignment requirement of the contained structure.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Acked-by: Christian Lamparter <chunkeey@xxxxxxxxx>

I've also applied this patch and a previous one dealing with VLAs to the firmware
source at <https://github.com/chunkeey/carl9170fw>. I did a quick rebuilt and
the same binary firmware was produced, so I think what's left is to update those
shared firmware/driver headers some day...

Cheers,
Christian