RE: [PATCH wireless-next] wifi: mac80211: add __packed to union members of struct ieee80211_rx_status

[Ping-Ke Shih <pkshih@realtek.com>]

Ping-Ke Shih <pkshih@realtek.com> wrote:
> The arm-linux-gnueabi-gcc compiler, align the field followed by union
> members, causing size of struct ieee80211_rx_status over skb->cb
> (48 bytes). By investigation, the union member starts at offset 32,
> and the offset of next field rate_idx is 36 instead of expected 33, and
> the total size is (unexpected) 52.
> 
> When compiling rtw88 driver, it throws:
> 
> In file included from /work/linux-src/linux-stable/include/linux/string.h:386,
>                  from /work/linux-src/linux-stable/include/linux/bitmap.h:13,
>                  from /work/linux-src/linux-stable/include/linux/cpumask.h:11,
>                  from /work/linux-src/linux-stable/include/linux/smp.h:13,
>                  from /work/linux-src/linux-stable/include/linux/lockdep.h:14,
>                  from /work/linux-src/linux-stable/include/linux/mutex.h:17,
>                  from /work/linux-src/linux-stable/include/linux/kernfs.h:11,
>                  from /work/linux-src/linux-stable/include/linux/sysfs.h:16,
>                  from /work/linux-src/linux-stable/include/linux/kobject.h:20,
>                  from /work/linux-src/linux-stable/include/linux/dmi.h:6,
>                  from pci.c:5:
> In function 'fortify_memcpy_chk',
>     inlined from 'rtw_pci_rx_napi.constprop' at pci.c:1095:4:
> /work/linux-src/linux-stable/include/linux/fortify-string.h:569:25: warning: call to
> '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st
> parameter); maybe use struct_group()? [-Wattribute-warning]
>   569 |                         __write_overflow_field(p_size_field, size);
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> After this patch, the size of struct ieee80211_rx_status is 48.
> 
> Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
> ---
> Because of size assertion of rtw88's efuse map [1], I found
> arm-linux-gnueabi-gcc compiler throws this warning, but x86 gcc is absolutely
> silent and expected without this patch.
> 
> [1]
> https://lore.kernel.org/linux-wireless/7c65e315-5a2e-455e-87ee-8fc6d60ed807@gmail.com/T/#m43fdf8a1
> c2b8cff92c1ef50faab7993522647162

I'd note that discussion thread [2] of original kernel test robot.
Arnd pointed out the cause is CONFIG_AEABI is not set, and he said
nobody should be using ARM OABI any more. 

Maybe, we can ignore the CPU and skip this patch.

[2] https://lore.kernel.org/lkml/6b6310b8-2b0d-4390-992e-5ccd81cef2e0@app.fastmail.com/