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    SubjectRe: [PATCH] kbuild: fix kernel/bounds.c 'W=1' warning
    On Mon, Oct 8, 2018 at 7:01 PM Kieran Bingham
    <kieran.bingham+renesas@ideasonboard.com> wrote:
    >
    > On 06/10/18 23:06, Masahiro Yamada wrote:
    > > On Sun, Oct 7, 2018 at 6:58 AM Masahiro Yamada
    > > <yamada.masahiro@socionext.com> wrote:
    > >>
    > >> Hi Miguel,
    > >>
    > >>
    > >> On Sun, Oct 7, 2018 at 6:18 AM Miguel Ojeda
    > >> <miguel.ojeda.sandonis@gmail.com> wrote:
    > >>>
    > >>> On Fri, Oct 5, 2018 at 10:35 AM Arnd Bergmann <arnd@arndb.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@grover:~/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@grover:~/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






    --
    Best Regards
    Masahiro Yamada

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