linux-kernel - Re: [patch V2 1/6] ARM: uaccess: Implement missing __get_user_asm

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Message-ID: <87plbo9awz.ffs@tglx>
Date: Wed, 17 Sep 2025 20:44:12 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: LKML <linux-kernel@...r.kernel.org>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>,
 kernel test robot <lkp@...el.com>, linux-arm-kernel@...ts.infradead.org,
 Nathan Chancellor <nathan@...nel.org>, Christophe Leroy
 <christophe.leroy@...roup.eu>, Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>, André Almeida
 <andrealmeid@...lia.com>, x86@...nel.org, Alexander Viro
 <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan
 Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org
Subject: Re: [patch V2 1/6] ARM: uaccess: Implement missing
 __get_user_asm_dword()

On Wed, Sep 17 2025 at 16:17, Russell King wrote:
> On Wed, Sep 17, 2025 at 03:55:10PM +0200, Thomas Gleixner wrote:
>> But it actually can be solved solvable by switching the casting to:
>> 
>>     (x) = *(__force __typeof__(*(ptr)) *) &__gu_val;
>> 
>> Not pretty, but after upping the frame size limit it builds an
>> allmodconfig kernel.
>
> For me, this produces:
>
> get-user-test.c:41:16: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
>    41 |         (x) = *(__force __typeof__(*(ptr)) *) &__gu_val;                \
>       |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> with arm-linux-gnueabihf-gcc (Debian 14.2.0-19) 14.2.0
>
> Maybe you're using a different compiler that doesn't issue that
> warning?

Yes :)

Was this with the one-line change or with the full conversion?

Thanks,

        tglx