linux-kernel - Re: [PATCH 16/27] modpost: make multiple export error

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Message-ID: <CAK7LNAR-u=EVzPL+iJHoBW62AK2ViD3nVnL79EdxNS03UxmkBA@mail.gmail.com>
Date:   Tue, 26 Apr 2022 13:08:45 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH 16/27] modpost: make multiple export error

On Tue, Apr 26, 2022 at 3:48 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Sun, Apr 24, 2022 at 12:09 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > This is currently a warning, but I think modpost should stop building
> > in this case.
> >
> > If the same symbol is exported multiple times and we let it keep going,
> > the sanity check becomes difficult.
> >
> > Only the legitimate case is that an external module overrides the
> > corresponding in-tree module to provide a different implementation
> > with the same interface.
>
> Could the same module export a weak version of a symbol, and a strong one?

No.  There is no concept like   EXPORT_SYMBOL_WEAK.

I am talking about kmod things.
You can modprobe an external module instead of the in-kernel one.

>
> Can kernel modules override in-kernel strong symbols?

Yes, I think so.


>
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  scripts/mod/modpost.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > index 14044cd94aaa..73f0b98e3b5a 100644
> > --- a/scripts/mod/modpost.c
> > +++ b/scripts/mod/modpost.c
> > @@ -411,9 +411,9 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod,
> >                 list_add_tail(&s->list, &mod->exported_symbols);
> >         } else if (!external_module || s->module->is_vmlinux ||
> >                    s->module == mod) {
> > -               warn("%s: '%s' exported twice. Previous export was in %s%s\n",
> > -                    mod->name, name, s->module->name,
> > -                    s->module->is_vmlinux ? "" : ".ko");
> > +               error("%s: '%s' exported twice. Previous export was in %s%s\n",
> > +                     mod->name, name, s->module->name,
> > +                     s->module->is_vmlinux ? "" : ".ko");
> >                 return s;
> >         }
> >
> > --
> > 2.32.0
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Best Regards
Masahiro Yamada