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

[Jeff Johnson]

On 5/11/2022 12:27 PM, Masahiro Yamada wrote:
> On Thu, May 12, 2022 at 3:48 AM Nick Desaulniers
> <ndesaulniers@xxxxxxxxxx> wrote:
> > On Mon, May 9, 2022 at 11:57 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> 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)