linux-kernel - Re: [PATCH] kbuild: fix kernel/bounds.c 'W=1' warning

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Message-ID: <CAMuHMdXv62=+jvFDb8w2vms4Zt4xm3Sf2K1i0BX7-1cwEtdCCA@mail.gmail.com>
Date:   Mon, 8 Oct 2018 16:41:01 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] kbuild: fix kernel/bounds.c 'W=1' warning

On Mon, Oct 8, 2018 at 4:33 PM Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> On Mon, Oct 8, 2018 at 7:01 PM Kieran Bingham
> <kieran.bingham+renesas@...asonboard.com> wrote:
> > On 06/10/18 23:06, Masahiro Yamada wrote:
> > > On Sun, Oct 7, 2018 at 6:58 AM Masahiro Yamada
> > > <yamada.masahiro@...ionext.com> wrote:
> > >>
> > >> Hi Miguel,
> > >>
> > >>
> > >> On Sun, Oct 7, 2018 at 6:18 AM Miguel Ojeda
> > >> <miguel.ojeda.sandonis@...il.com> wrote:
> > >>>
> > >>> On Fri, Oct 5, 2018 at 10:35 AM Arnd Bergmann <arnd@...db.de> wrote:
> > >>>>
> > >>>> Building any configuration with 'make W=1' produces a warning:
> > >>>>
> > >>>> kernel/bounds.c:16:6: warnign: no previous prototype for 'foo' [-Wmissing-prototypes]
> > >>>>
> > >>>> When also passing -Werror, this prevents us from building any
> > >>>> other files. Nobody ever calls the function, but we can't make
> > >>>> it 'static' either since we want the compiler output.
> > >>>>
> > >>>> Calling it 'main' instead however avoids the warning, because gcc
> > >>>> does not insist on having a declaration for main.
> > >>>
> > >>> I think marking the function as static __used should do the trick and
> > >>> would be less confusing.
> > >>
> > >>
> > >>
> > >>
> > >> I tried __used, but I still see the warning.
> > >>
> > >>
> > >> masahiro@...ver:~/ref/linux$ git diff
> > >> diff --git a/kernel/bounds.c b/kernel/bounds.c
> > >> index c373e88..aee0101 100644
> > >> --- a/kernel/bounds.c
> > >> +++ b/kernel/bounds.c
> > >> @@ -13,7 +13,7 @@
> > >>  #include <linux/log2.h>
> > >>  #include <linux/spinlock_types.h>
> > >>
> > >> -void foo(void)
> > >> +void __used foo(void)
> > >>  {
> > >>         /* The enum constants to put into include/generated/bounds.h */
> > >>         DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
> > >> masahiro@...ver:~/ref/linux$ make W=1  prepare
> > >>   CC      kernel/bounds.s
> > >> kernel/bounds.c:16:13: warning: no previous prototype for ‘foo’
> > >> [-Wmissing-prototypes]
> > >>  void __used foo(void)
> > >>              ^
> > >>   CC      arch/x86/kernel/asm-offsets.s
> > >
> > >
> > >
> > > Sorry, I forgot to add 'static'.
> > >
> > > Adding both static and __used worked for me,
> > > and I like the idea.
> > >
> >
> > Aha - I'd also tried converting to static in my earlier attempts, but
> > didn't realise we had __used!
> >
> > updating as "static __used" causes the following diff:
> >
> > diff -Nurp bounds.s.foo bounds.s.static-used
> > --- bounds.s.foo        2018-10-05 10:20:53.269941404 +0100
> > +++ bounds.s.static-used        2018-10-08 10:51:18.079309049 +0100
> > @@ -110,7 +110,6 @@
> >  #NO_APP
> >         .align  2
> >         .p2align 3,,7
> > -       .global foo
> >         .type   foo, %function
> >  foo:
> >         stp     x29, x30, [sp, -16]!    //,,,
> >
> >
> > I'd say this is a pretty good alternative fix - however I see Arnd's
> > version is already on it's way though akpm's tree...
> >
> > https://ozlabs.org/~akpm/mmots/broken-out/kbuild-fix-kernel-boundsc-w%3D1-warning.patch
> >
> > Anyway, as long as one of the variants gets there I'll be happy :)
>
>
> I will leave it to Arnd.
>
>
> When we fix arch/{mips,sparc}/kernel/asm-offsets.c,
> 'static __used' is just additions.
>
> The 'main(void)' solution would require a little bit restructuring.
>
>
>
> FWIW, with my quick analysis, the following should be fixed as well:
>
> arch/alpha/kernel/asm-offsets.c
> arch/c6x/kernel/asm-offsets.c
> arch/ia64/kernel/asm-offsets.c
> arch/ia64/kernel/nr-irqs.c
> arch/mips/kernel/asm-offsets.c
> arch/riscv/kernel/asm-offsets.c
> arch/sparc/kernel/asm-offsets.c
> arch/x86/kernel/asm-offsets.c
> arch/x86/um/shared/sysdep/kernel-offsets.h
> samples/bpf/syscall_nrs.c

All the other asm-offsets.c files already use "int main(void)" ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds