linux-kernel - Re: [PATCH] x86: select ARCH_WANT_FRAME_POINTERS again when UNWINDER_FRAME

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Date: Fri, 17 May 2024 16:18:06 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: x86@...nel.org
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: select ARCH_WANT_FRAME_POINTERS again when UNWINDER_FRAME_POINTER=y

Hi, x86 maintainers


Please check this.


And, please also note the current code is incorrect,
and it may get broken with future Kconfig refactoring.





On Thu, Mar 21, 2024 at 12:30 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Ping?
>
>
> On Sun, Feb 4, 2024 at 9:20 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > It took me some time to understand the purpose of the tricky code at
> > the end of arch/x86/Kconfig.debug.
> >
> > Without it, the following would be shown:
> >
> >   WARNING: unmet direct dependencies detected for FRAME_POINTER
> >
> > because commit 81d387190039 ("x86/kconfig: Consolidate unwinders into
> > multiple choice selection") removed 'select ARCH_WANT_FRAME_POINTERS'.
> >
> > The correct and more straightforward approach should have been to move
> > it where 'select FRAME_POINTER' is located.
> >
> > Several architectures properly handle the conditional selection of
> > ARCH_WANT_FRAME_POINTERS. For example, 'config UNWINDER_FRAME_POINTER'
> > in arch/arm/Kconfig.debug.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  arch/x86/Kconfig.debug | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> > index c5d614d28a75..74777a97e394 100644
> > --- a/arch/x86/Kconfig.debug
> > +++ b/arch/x86/Kconfig.debug
> > @@ -248,6 +248,7 @@ config UNWINDER_ORC
> >
> >  config UNWINDER_FRAME_POINTER
> >         bool "Frame pointer unwinder"
> > +       select ARCH_WANT_FRAME_POINTERS
> >         select FRAME_POINTER
> >         help
> >           This option enables the frame pointer unwinder for unwinding kernel
> > @@ -271,7 +272,3 @@ config UNWINDER_GUESS
> >           overhead.
> >
> >  endchoice
> > -
> > -config FRAME_POINTER
> > -       depends on !UNWINDER_ORC && !UNWINDER_GUESS
> > -       bool
> > --
> > 2.40.1
> >
>
>
> --
> Best Regards
> Masahiro Yamada



--
Best Regards
Masahiro Yamada