RE: include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(struct rtw8814a_efuse) == 512"

[Ping-Ke Shih]

Hi Geert,
> Hi Ping-Ke,
> 
> On Fri, 10 Apr 2026 at 14:15, Ping-Ke Shih <pkshih@xxxxxxxxxxx> wrote:
> > Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx> wrote:
> > > On 10/04/2026 12:25, kernel test robot wrote:
> > > > tree:    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > > head:   9a9c8ce300cd3859cc87b408ef552cd697cc2ab7
> > > > commit: deb3ddeb18652118956fb581a39ac299e1ee5623 wifi: rtw88: Enable the new RTL8814AE/RTL8814AU
> drivers
> > > > date:   1 year, 1 month ago
> > > > config: arm-randconfig-001-20260410
> (https://download.01.org/0day-ci/archive/20260410/202604101721.fsv5XmCX-lkp@xxxxxxxxx/config)
> > > > compiler: arm-linux-gnueabi-gcc (GCC) 8.5.0
> > > > reproduce (this is a W=1 build):
> (https://download.01.org/0day-ci/archive/20260410/202604101721.fsv5XmCX-lkp@xxxxxxxxx/reproduce)
> > > >
> > > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > > the same patch/commit), kindly add following tags
> > > > | Fixes: deb3ddeb1865 ("wifi: rtw88: Enable the new RTL8814AE/RTL8814AU drivers")
> > > > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > > | Closes:  https://lore.kernel.org/oe-kbuild-all/202604101721.fsv5XmCX-lkp@xxxxxxxxx/
> > > >
> > > > All errors (new ones prefixed by >>):
> > > >
> > > >    In file included from include/linux/bitfield.h:10,
> > > >                     from include/linux/fortify-string.h:5,
> > > >                     from include/linux/string.h:389,
> > > >                     from include/linux/uuid.h:11,
> > > >                     from include/linux/mod_devicetable.h:14,
> > > >                     from include/linux/usb.h:5,
> > > >                     from drivers/net/wireless/realtek/rtw88/rtw8814a.c:5:
> > > >>> include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(struct rtw8814a_efuse)
> == 512"
> > >
> > > struct rtw_2g_txpwr_idx is missing __packed. Could that be the reason
> > > for the error? I don't see what else could be causing it.
> > >
> >
> > I also found that flaw, but it isn't cause. I download cross compiler
> > to build arm on my x86, and address the cause is:
> >
> > diff --git a/drivers/net/wireless/realtek/rtw88/rtw8814a.h
> b/drivers/net/wireless/realtek/rtw88/rtw8814a.h
> > index c57c7c8f915e..7f2260117487 100644
> > --- a/drivers/net/wireless/realtek/rtw88/rtw8814a.h
> > +++ b/drivers/net/wireless/realtek/rtw88/rtw8814a.h
> > @@ -51,10 +51,15 @@ struct rtw8814a_efuse {
> >         union {
> >                 struct rtw8814au_efuse u;
> >                 struct rtw8814ae_efuse e;
> > -       };
> > +       } __packed;
> 
> How can that make a difference?
> Both rtw8814au_efuse and rtw8814ae_efuse contain just (the same number
> of) bytes, so __packed on the union should not make any difference?
> Moreover, rtw8814au_efuse and rtw8814ae_efuse are already tagged with
> __packed, which should also not make any difference.  Someone's been
> sprinkling too many __packed all over the place?

I have similar thought as yours, but arm-linux-gnueabi-gcc compiler seems
have special treatment with union. For this case, without __packed
the offset of followed field res5 will become 0xe0.

When investing this error, I also found another waning [1].

I don't know why the compiler treats the union so special, and I fix
them by experimental results.

[1] https://lore.kernel.org/linux-wireless/20260411072509.1556635-1-pkshih@xxxxxxxxxxx/T/#u

> 
> >         u8 res5[0x122];                 /* 0xde */
> >  } __packed;
> >
> > I will send a patch soon.
> >
> > Ping-Ke
> 
> Gr{oetje,eeting}s,
> 
>                         Geert

Ping-Ke