linux-kernel - Re: [PATCH v2] kbuild: fix UNUSED_KSYMS

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Date:   Fri, 26 Feb 2021 10:25:50 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2] kbuild: fix UNUSED_KSYMS_WHITELIST for Clang LTO

On Fri, Feb 26, 2021 at 7:26 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Commit fbe078d397b4 ("kbuild: lto: add a default list of used symbols")
> does not work as expected if the .config file has already specified
> CONFIG_UNUSED_KSYMS_WHITELIST="my/own/white/list" before enabling
> CONFIG_LTO_CLANG.
>
> So, the user-supplied whitelist and LTO-specific white list must be
> independent of each other.
>
> I refactored the shell script so CONFIG_MODVERSIONS and CONFIG_CLANG_LTO
> handle whitelists in the same way.
>
> Fixes: fbe078d397b4 ("kbuild: lto: add a default list of used symbols")
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
> Changes in v2:
>   - Rebase on top of Arnd's patch:
>     https://lore.kernel.org/lkml/20210225143456.3829513-1-arnd@kernel.org/
>
>  init/Kconfig                    |  1 -
>  scripts/gen_autoksyms.sh        | 35 ++++++++++++++++++++++++---------
>  scripts/lto-used-symbollist.txt |  6 ------

People who want to use their own "white-listed" (allow-listed)
symbollist-file can do that via
CONFIG_UNUSED_KSYMS_WHITELIST="my/own/white/list".
Correct?

Why do you delete the default "scripts/lto-used-symbollist.txt" file
and remove the default in the appropriate Kconfig for people who want
to enable Clang-(Thin)LTO?
These people should now use
CONFIG_UNUSED_KSYMS_WHITELIST="scripts/lto-used-symbollist.txt"?
But again - the file was deleted with your patch.
Do I miss something?

- Sedat -

>  3 files changed, 26 insertions(+), 16 deletions(-)
>  delete mode 100644 scripts/lto-used-symbollist.txt
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 719871f8727c..64c32300d1b4 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -2283,7 +2283,6 @@ config TRIM_UNUSED_KSYMS
>  config UNUSED_KSYMS_WHITELIST
>         string "Whitelist of symbols to keep in ksymtab"
>         depends on TRIM_UNUSED_KSYMS
> -       default "scripts/lto-used-symbollist.txt" if LTO_CLANG
>         help
>           By default, all unused exported symbols will be un-exported from the
>           build when TRIM_UNUSED_KSYMS is selected.
> diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh
> index d54dfba15bf2..da320151e7c3 100755
> --- a/scripts/gen_autoksyms.sh
> +++ b/scripts/gen_autoksyms.sh
> @@ -19,7 +19,26 @@ esac
>  # We need access to CONFIG_ symbols
>  . include/config/auto.conf
>
> -ksym_wl=/dev/null
> +needed_symbols=
> +
> +# Special case for modversions (see modpost.c)
> +if [ -n "$CONFIG_MODVERSIONS" ]; then
> +       needed_symbols="$needed_symbols module_layout"
> +fi
> +
> +# With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a binary
> +# when the .mod files are generated, which means they don't yet contain
> +# references to certain symbols that will be present in the final binaries.
> +if [ -n "$CONFIG_LTO_CLANG" ]; then
> +       # intrinsic functions
> +       needed_symbols="$needed_symbols memcpy memmove memset"
> +       # ftrace
> +       needed_symbols="$needed_symbols _mcount"
> +       # stack protector symbols
> +       needed_symbols="$needed_symbols __stack_chk_fail __stack_chk_guard"
> +fi
> +
> +ksym_wl=
>  if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then
>         # Use 'eval' to expand the whitelist path and check if it is relative
>         eval ksym_wl="$CONFIG_UNUSED_KSYMS_WHITELIST"
> @@ -40,16 +59,14 @@ cat > "$output_file" << EOT
>  EOT
>
>  [ -f modules.order ] && modlist=modules.order || modlist=/dev/null
> -sed 's/ko$/mod/' $modlist |
> -xargs -n1 sed -n -e '2{s/ /\n/g;/^$/!p;}' -- |
> -cat - "$ksym_wl" |
> +
> +{
> +       sed 's/ko$/mod/' $modlist | xargs -n1 sed -n -e '2p'
> +       echo "$needed_symbols"
> +       [ -n "$ksym_wl" ] && cat "$ksym_wl"
> +} | sed -e 's/ /\n/g' | sed -n -e '/^$/!p' |
>  # Remove the dot prefix for ppc64; symbol names with a dot (.) hold entry
>  # point addresses.
>  sed -e 's/^\.//' |
>  sort -u |
>  sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$output_file"
> -
> -# Special case for modversions (see modpost.c)
> -if [ -n "$CONFIG_MODVERSIONS" ]; then
> -       echo "#define __KSYM_module_layout 1" >> "$output_file"
> -fi
> diff --git a/scripts/lto-used-symbollist.txt b/scripts/lto-used-symbollist.txt
> deleted file mode 100644
> index 406ada65e926..000000000000
> --- a/scripts/lto-used-symbollist.txt
> +++ /dev/null
> @@ -1,6 +0,0 @@
> -memcpy
> -memmove
> -memset
> -_mcount
> -__stack_chk_fail
> -__stack_chk_guard
> --
> 2.27.0
>
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