linux-kernel - Re: [PATCH v3 6/7] asm-generic: percpu: Add assembly guard

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Message-Id: <20250915152930.2654981-1-tiwei.bie@linux.dev>
Date: Mon, 15 Sep 2025 23:29:30 +0800
From: Tiwei Bie <tiwei.bie@...ux.dev>
To: arnd@...db.de
Cc: richard@....at,
	anton.ivanov@...bridgegreys.com,
	johannes@...solutions.net,
	benjamin@...solutions.net,
	linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-um@...ts.infradead.org,
	tiwei.btw@...group.com,
	tiwei.bie@...ux.dev
Subject: Re: [PATCH v3 6/7] asm-generic: percpu: Add assembly guard

On Mon, 15 Sep 2025 09:40:35 +0200, Arnd Bergmann wrote:
> On Sun, Sep 14, 2025, at 17:56, Tiwei Bie wrote:
> > From: Tiwei Bie <tiwei.btw@...group.com>
> >
> > Currently, asm/percpu.h is directly or indirectly included by
> > some assembly files on x86. Some of them (e.g., checksum_32.S)
> > are also used on um. But x86 and um provide different versions
> > of asm/percpu.h -- um uses asm-generic/percpu.h directly.
> >
> > When SMP is enabled, asm-generic/percpu.h will introduce C code
> > that cannot be assembled. Since asm-generic/percpu.h currently
> > is not designed for use in assembly, and these assembly files
> > do not actually need asm/percpu.h on um, let's add the assembly
> > guard in asm-generic/percpu.h to fix this issue.
> >
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: linux-arch@...r.kernel.org
> > Signed-off-by: Tiwei Bie <tiwei.btw@...group.com>
> 
> Have you tried if you can remove the percpu.h dependency from
> the files that currently include it? In many cases it should
> be enough to use percpu-defs.h.

It doesn't seem to work. The indirect inclusion of asm/percpu.h
comes from asm/nospec-branch.h, which expands DECLARE_PER_CPU()
and thus requires asm/percpu.h.

> 
> If that doesn't work, I have no objections to this patch either.
> 
> Acked-by: Arnd Bergmann <arnd@...db.de>

Thanks! :)

Regards,
Tiwei