linux-kernel - Re: [PATCH 1/5] ARC: uapi: Stop leaking CONFIG_ARC_HAS

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Message-ID: <20260102085226-c6463fff-042d-4654-8721-27e995f06c7c@linutronix.de>
Date: Fri, 2 Jan 2026 08:55:10 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Arnd Bergmann <arnd@...db.de>
Cc: Vineet Gupta <vgupta@...nel.org>, Russell King <linux@...linux.org.uk>, 
	Dinh Nguyen <dinguyen@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/5] ARC: uapi: Stop leaking CONFIG_ARC_HAS_SWAPE
 reference to userspace

On Tue, Dec 30, 2025 at 10:23:08PM +0100, Arnd Bergmann wrote:
> On Tue, Dec 30, 2025, at 08:10, Thomas Weißschuh wrote:
> > UAPI headers are not supposed to leak references to kconfig symbols.
> > These won't be set when building userspace. Hide the kconfig reference
> > behind 'if defined(__KERNEL__)', so it will be stripped by
> > headers_install.sh. The result for userspace will be the same, but the
> > exception in headers_install.sh can also be removed.
> >
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> 
> Acked-by: Arnd Bergmann <arnd@...db.de>
> 
> Same as for the nios2 version, I think the nicer solution would
> be to use the asm-generic header for uapi and move this one
> to arch/arc/include/asm/swab.h for kernel-internal use.

Ack. Also to your other feedback on the series.

> In theory, using 'select ARCH_USE_BUILTIN_BSWAP' in Kconfig should
> let the compiler pick the best swap instruction, which would
> be even less code, but I'm not sure if there was a reason that
> nios2 and arc don't already do this.

I'd like to keep the current logic to avoid potential issues.
But maybe the arch maintainers will chime in.


Thomas