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

[Arnd Bergmann]

On Mon, Apr 13, 2026, at 11:15, Geert Uytterhoeven wrote:
> On Mon, 13 Apr 2026 at 02:48, Ping-Ke Shih <pkshih@xxxxxxxxxxx> wrote:
>> > On Fri, 10 Apr 2026 at 14:15, Ping-Ke Shih <pkshih@xxxxxxxxxxx> wrote:
>> > 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.
>
> Hmm, I can confirm the original issue, and that adding __packed does
> have an impact (it reduces the size of rtw8814a_efuse from 522 to 520),
> but the actual size is still wrong (should be 512).
>
> drivers/net/wireless/realtek/rtw88/rtw88xxa.h has a similar issue, but
> adding __packed does not make a difference there.
>
> Removing the __packed from struct rtw8814au_efuse increases its size
> from 14 to 16 bytes.  Looks like that ABI pads every structure to a
> multiple of 4 bytes?

Correct, that is a unique property of the ARM "OABI" legacy ABI,
triggered by this defconfig line:

# CONFIG_AEABI is not set

Nobody should be using ARM OABI any more, and I think we should
remove it from the kernel once support for the StrongARM
CPU gets removed (I have patches for that), as those CPUs were
the last ones that regularly used OABI.

Annotating the union as '__packed' is the correct fix for
the theoretical users of OABI, and does nothing on other
supported targets in Linux.

       Arnd