linux-kernel - Re: [PATCH 1/4] rtw88: Add packed attribute to the eFuse structs

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Date:   Wed, 4 Jan 2023 18:49:01 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Ping-Ke Shih <pkshih@...ltek.com>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "kvalo@...nel.org" <kvalo@...nel.org>,
        "tehuang@...ltek.com" <tehuang@...ltek.com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "tony0620emma@...il.com" <tony0620emma@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] rtw88: Add packed attribute to the eFuse structs

On Wed, Jan 4, 2023 at 5:31 PM David Laight <David.Laight@...lab.com> wrote:
[...]
> > > What you may want to do is add compile-time asserts for the
> > > sizes of the structures.
> > Do I get you right that something like:
> >   BUILD_BUG_ON(sizeof(rtw8821c_efuse) != 256);
> > is what you have in mind?
>
> That looks like the one...
I tried this (see the attached patch - it's just meant to show what I
did, it's not meant to be applied upstream).
With the attached patch but no other patches this makes the rtw88
driver compile fine on 6.2-rc2.

Adding __packed to struct rtw8723d_efuse changes the size of that
struct for me (I'm compiling for AArch64 / ARM64).
With the packed attribute it has 267 bytes, without 268 bytes.

Do you have any ideas as to why that is?


Best regards,
Martin

View attachment "add-build-bug-on.patch" of type "text/x-patch" (1988 bytes)