linux-kernel - Re: [PATCH] lib: fix kconfig dependency on ARCH_WANT_FRAME

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Message-ID: <20857798.apSVmgY6Dz@ubuntu-mate-laptop>
Date:   Wed, 24 Mar 2021 02:48:26 -0400
From:   Julian Braha <julianbraha@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib: fix kconfig dependency on ARCH_WANT_FRAME_POINTERS

On Monday, March 22, 2021 3:43:41 AM EDT you wrote:
> Hi Julian,
> 
> On Sun, Mar 21, 2021 at 11:40 PM Julian Braha <julianbraha@...il.com> wrote:
> > On Sunday, March 21, 2021 2:28:43 PM EDT you wrote:
> > > On Sat, Mar 20, 2021 at 1:17 AM Julian Braha <julianbraha@...il.com> wrote:
> > > > When LATENCYTOP is enabled and ARCH_WANT_FRAME_POINTERS
> > > > is disabled, Kbuild gives the following warning:
> > > >
> > > > WARNING: unmet direct dependencies detected for FRAME_POINTER
> > > >   Depends on [n]: DEBUG_KERNEL [=y] && (M68K || UML || SUPERH) || ARCH_WANT_FRAME_POINTERS [=n] || MCOUNT [=n]
> > > >   Selected by [y]:
> > > >   - LATENCYTOP [=y] && DEBUG_KERNEL [=y] && STACKTRACE_SUPPORT [=y] && PROC_FS [=y] && !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM && !ARC && !X86
> > > >
> > > > This is because LATENCYTOP selects FRAME_POINTER,
> > > > without selecting or depending on ARCH_WANT_FRAME_POINTERS,
> > > > despite FRAME_POINTER depending on ARCH_WANT_FRAME_POINTERS.
> > > >
> > > > Signed-off-by: Julian Braha <julianbraha@...il.com>
> > >
> > > Thanks for your patch!
> > >
> > > > --- a/lib/Kconfig.debug
> > > > +++ b/lib/Kconfig.debug
> > > > @@ -1675,6 +1675,7 @@ config LATENCYTOP
> > > >         depends on DEBUG_KERNEL
> > > >         depends on STACKTRACE_SUPPORT
> > > >         depends on PROC_FS
> > > > +       select ARCH_WANT_FRAME_POINTERS if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM && !ARC && !X86
> > >
> > > ARCH_WANT_FRAME_POINTERS is a symbol that is only to be selected by
> > > architecture-specific configuration, and must not be overridden:
> > >
> > >     # Select this config option from the architecture Kconfig, if it
> > >     # is preferred to always offer frame pointers as a config
> > >     # option on the architecture (regardless of KERNEL_DEBUG):
> > >
> > > Probably this should be turned into a depends instead?
> > >
> > > >         select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM && !ARC && !X86
> > > >         select KALLSYMS
> > > >         select KALLSYMS_ALL
> 
> > Making this a 'depends' causes a recursive dependency error.
> > Any other ideas?
> 
> What about
> 
>     -select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE &&
> !ARM && !ARC && !X86
>     +depends on FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE
> && !ARM && !ARC && !X86
> 
> ?
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> 

Hi Geert,

Sadly, this won't work either. In Kconfig, 'depends' cannot have an 'if' after it (only 'select' can.)
Kbuild gives an error for this.

- Julian Braha