From: Arnd Bergmann > Sent: 04 February 2021 16:29 > > 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. I think I'd add compile-time assert that some of these structures are exactly the expected size. Then look at removing the outer packed/aligned attributes and just putting the attribute on the 16/32 bit member(s) that themselves might be misaligned. Much the way that the 32bit aligned 64bit values are handled in the x86 compat code in x86-64. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
