linux-kernel - Re: [PATCH] compiler.h: Avoid the usage of __typeof_unqual__() when __GENKSYMS_

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Message-ID: <CAFULd4aLMF_2AbUAvpYw+o1qo6U-Ya_+Ewy-wW17g-r-MBF9_g@mail.gmail.com>
Date: Sun, 13 Apr 2025 23:18:14 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-modules@...r.kernel.org, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Paul Menzel <pmenzel@...gen.mpg.de>, 
	Sami Tolvanen <samitolvanen@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] compiler.h: Avoid the usage of __typeof_unqual__() when
 __GENKSYMS__ is defined

On Sun, Apr 6, 2025 at 5:36 PM Uros Bizjak <ubizjak@...il.com> wrote:

> > You are still seeing the warnings because __typeof_unqual__
> > is not only the issue.
> >
> > Hint:
> >
> > $ make -s KCFLAGS=-D__GENKSYMS__  arch/x86/kernel/setup_percpu.i
> > $ grep  'this_cpu_off;'  arch/x86/kernel/setup_percpu.i
>
> I see.
>
> With my workaround, this_cpu_off is declared as:
>
> extern __attribute__((section(".data..percpu" "..hot.."
> "this_cpu_off"))) __typeof__(unsigned long) this_cpu_off;
>
> while without workaround, the same variable is declared as:
>
> extern __seg_gs __attribute__((section(".data..percpu" "..hot.."
> "this_cpu_off"))) __typeof__(unsigned long) this_cpu_off;
>
> It looks that genksyms should be extended to handle (or ignore)
> __seg_gs/__seg_fs named address prefix. Somewhat surprising, because
> genksyms can process:
>
> extern __attribute__((section(".data..percpu" "..hot.."
> "const_current_task"))) __typeof__(struct task_struct * const
> __seg_gs) const_current_task
>
> without problems.
>
> I'm sorry, but I'm not able to extend genksyms with a new keyword by myself...

The following patch that handles typeof_unqual() as typeof(), and in
addition ignores __seg_gs similar to how other type qualifiers are
ignored, avoids genksyms errors.

Uros.

View attachment "p.diff.txt" of type "text/plain" (1633 bytes)