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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Thu, 12 May 2022 04:27:37 +0900
Message-ID: <CAK7LNAR5preB59HJH1-F_ZfEmoF3N8b9z4eRhYzsEVwu_XUH4Q@mail.gmail.com>
Subject: Re: [PATCH v4 03/14] modpost: split the section mismatch checks into section-check.c
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nicolas Schier <nicolas@fjasle.eu>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-modules <linux-modules@vger.kernel.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        clang-built-linux <llvm@lists.linux.dev>
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On Thu, May 12, 2022 at 3:48 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Mon, May 9, 2022 at 11:57 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > > > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > > > index a78b75f0eeb0..e7e2c70a98f5 100644
> > > > --- a/scripts/mod/modpost.c
> > > > +++ b/scripts/mod/modpost.c
> > > > @@ -31,7 +31,7 @@ static bool external_module;
> > > >  /* Only warn about unresolved symbols */
> > > >  static bool warn_unresolved;
> > > >
> > > > -static int sec_mismatch_count;
> > > > +int sec_mismatch_count;
> > >
> > > ^ this should go in modpost.h if it is to be used in two translation
> > > units, rather than forward declaring it in section-check.c.  You did
> > > this for the functions.
> >
> >
> > Sorry, I do not understand.
> >
> >
> > In modpost.h, I put the declaration:
> >
> >   extern int sec_mismatch_count;
> >
> > If I moved it to the header without 'extern'
> > I would get multiple definitions.
>
> Yeah, you need to _declare_ it w/ extern in the header, then _define_
> it in one source file.
>
> That way, if the type ever changes, the sources will agree on type in
> all source files. You will get a redefinition error if the definition
> changes the type of the variable since the last declaration.
>
> What you're doing is forward declaring, which works, and is a common
> pattern for (bloated) C++, but is less type safe than sharing a single
> common declaration between multiple source files via a single common
> shared header. (Sorry I didn't respond before you sent v5)

Sorry, I still do not understand your suggestion.


Could you provide me with a code diff
showing how to do this better?


-- 
Best Regards
Masahiro Yamada