linux-kernel - Re: [PATCH] kbuild: Ignore __this_module in gen

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Date:   Fri, 17 Jun 2022 10:28:14 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Sami Tolvanen <samitolvanen@...gle.com>,
        Ramji Jiyani <ramjiyani@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Alexander Lobakin <alobakin@...me>,
        Steve Muckle <smuckle@...gle.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [PATCH] kbuild: Ignore __this_module in gen_autoksyms.sh

+ 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@...gle.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.

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.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