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

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Message-ID: <20250917171424.GB1457869@ax162>
Date: Wed, 17 Sep 2025 10:14:24 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	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,
	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 04:17:38PM +0100, Russell King (Oracle) wrote:
> 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?

Maybe because the kernel uses -fno-strict-aliasing, which presumably
turns off -Wstrict-aliasing?

Cheers,
Nathan