linux-kernel - Re: [PATCH v4 03/14] modpost: split the section mismatch checks into section-check.c

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Date:   Wed, 11 May 2022 13:01:13 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Jeff Johnson <quic_jjohnson@...cinc.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-modules <linux-modules@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        clang-built-linux <llvm@...ts.linux.dev>
Subject: Re: [PATCH v4 03/14] modpost: split the section mismatch checks into section-check.c

On Wed, May 11, 2022 at 12:51 PM Jeff Johnson <quic_jjohnson@...cinc.com> wrote:
>
> On 5/11/2022 12:27 PM, Masahiro Yamada wrote:
> > On Thu, May 12, 2022 at 3:48 AM Nick Desaulniers
> > <ndesaulniers@...gle.com> wrote:
> >>
> >> On Mon, May 9, 2022 at 11:57 PM Masahiro Yamada <masahiroy@...nel.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?
>
> I think you are doing exactly what he's asking for:
> declare it with extern in the header (modpost.h change)
> define it in one source file (modpost.c change)
>

Oh! Indeed, sorry, I'm getting lost here in the review. Sorry for the
noise then.
-- 
Thanks,
~Nick Desaulniers