linux-kernel - Re: [PATCH] kbuild: do not automatically add -w option to modpost

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Date:   Tue, 24 Jan 2023 11:48:15 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     William McVicker <willmcvicker@...gle.com>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH] kbuild: do not automatically add -w option to modpost

On Tue, Jan 24, 2023 at 7:42 AM William McVicker
<willmcvicker@...gle.com> wrote:
>
> On 01/23/2023, Masahiro Yamada wrote:
> > When there is a missing input file (vmlinux.o or Module.symvers), you
> > are likely to get a ton of unresolved symbols.
> >
> > Currently, Kbuild automatically adds the -w option to allow module builds
> > to continue with warnings instead of errors.
> >
> > This may not be what the user expects because it is generally more useful
> > to catch all possible issues at build time instead of at run time.
> >
> > Let's not do what the user did not ask.
> >
> > If you still want to build modules anyway, you can proceed by explicitly
> > setting KBUILD_MODPOST_WARN=1. Since you may miss a real issue, you need
> > to be aware of what you are doing.
> >
> > Suggested-by: William McVicker <willmcvicker@...gle.com>
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  scripts/Makefile.modpost | 8 +++-----
> >  1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> > index 43343e13c542..9254ed811ddd 100644
> > --- a/scripts/Makefile.modpost
> > +++ b/scripts/Makefile.modpost
> > @@ -121,16 +121,14 @@ modpost-args += -e $(addprefix -i , $(KBUILD_EXTRA_SYMBOLS))
> >
> >  endif # ($(KBUILD_EXTMOD),)
> >
> > -ifneq ($(missing-input),)
> > -modpost-args += -w
> > -endif
> > -
> >  quiet_cmd_modpost = MODPOST $@
> >        cmd_modpost = \
> >       $(if $(missing-input), \
> >               echo >&2 "WARNING: $(missing-input) is missing."; \
> >               echo >&2 "         Modules may not have dependencies or modversions."; \
> > -             echo >&2 "         You may get many unresolved symbol warnings.";) \
> > +             echo >&2 "         You may get many unresolved symbol errors.";) \
>
> You need to move the closing parenthesis to come at the end of these
> echo messages. Otherwise you get this new message unconditionally.


Ah, thanks for catching it.


> I also found during testing that the refactoring in commit f73edc8951b2
> ("kbuild: unify two modpost invocations") dropped the check for missing
> KBUILD_EXTRA_SYMBOLS. That means if an external module depends on
> another external module and sets:
>
>   KBUILD_EXTRA_SYMBOLS=/path/to/ext_module/Module.symvers
>
> ... then make will fail even with KBUILD_MODPOST_WARN=1 since we
> unconditionally add KBUILD_EXTRA_SYMBOLS to the modpost-args like this:
>
>   modpost-args += -e $(addprefix -i , $(KBUILD_EXTRA_SYMBOLS))
>
> To fix this, I suggest you also take the following patch so that
> KBUILD_MODPOST_WARN=1 will allow you to skip those unresolved symbols as
> well:


How is this useful?

KBUILD_EXTRA_SYMBOLS is explicitly specified by the user
via the command line or the environment variable.

If $(KBUILD_EXTRA_SYMBOLS) does not exist,
it is a user's fault, isn't it?






-- 
Best Regards
Masahiro Yamada