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From:   Ramji Jiyani <ramjiyani@google.com>
Date:   Fri, 17 Jun 2022 11:14:42 -0700
Message-ID: <CAKUd0B_2PcLW5Lj+4rG=AeVKBQx86x5bM2zL2YGORfKsk1EFyQ@mail.gmail.com>
Subject: Re: [PATCH] kbuild: Ignore __this_module in gen_autoksyms.sh
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Sami Tolvanen <samitolvanen@google.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nicolas Schier <nicolas@fjasle.eu>,
        Alexander Lobakin <alobakin@pm.me>,
        Steve Muckle <smuckle@google.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Sedat Dilek <sedat.dilek@gmail.com>
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On Fri, Jun 17, 2022 at 10:28 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> + Sedat
> Re: https://lore.kernel.org/linux-kbuild/CAKwvOdmb5xdF70TzNp=4STCpzkGh16FnuKE1KbdzDhHt=OuRFA@mail.gmail.com/
> In case this helps.
>
> + Ramji
> Ramji, it sounds like you helped test this downstream? If that's the
> case, mind supplying your tested-by tag for the record? Thanks for
> help verifying this change. Thanks too, Steve!
>
> On Thu, Jun 16, 2022 at 12:58 PM Sami Tolvanen <samitolvanen@google.com> wrote:
> >
> > Module object files can contain an undefined reference to __this_module,
> > which isn't resolved until we link the final .ko. The kernel doesn't
> > export this symbol, so ignore it in gen_autoksyms.sh. This avoids an
> > unnecessary vmlinux rebuild with UNUSED_KSYMS_WHITELIST when we have a
> > symbol list that already contains all the module dependencies.
>
> Worth mentioning that this also fixes a significant build time
> regression made more painful by CONFIG_LTO_CLANG_FULL when using
> CONFIG_UNUSED_KSYMS_WHITELIST.
>

Yes, I tested it and it resolves the build time regression with modules.

Tested-by: Ramji Jiyani <ramjiyani@google.com>

Thanks,
Ramji

> Thanks for the patch!
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > ---
> >  scripts/gen_autoksyms.sh | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh
> > index faacf7062122..653fadbad302 100755
> > --- a/scripts/gen_autoksyms.sh
> > +++ b/scripts/gen_autoksyms.sh
> > @@ -56,4 +56,7 @@ EOT
> >  # point addresses.
> >  sed -e 's/^\.//' |
> >  sort -u |
> > +# Ignore __this_module. It's not an exported symbol, and will be resolved
> > +# when the final .ko's are linked.
> > +grep -v '^__this_module$' |
> >  sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$output_file"
> > --
> > 2.36.1.476.g0c4daa206d-goog
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers