Re: [PATCH 1/4] kbuild: fix UNUSED_KSYMS_WHITELIST for Clang LTO
From: Sami Tolvanen
Date: Thu Feb 25 2021 - 12:46:56 EST
Hi Masahiro,
On Thu, Feb 25, 2021 at 8:03 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
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Commit fbe078d397b4 ("kbuild: lto: add a default list of used symbols")
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does not work as expected if the .config file has already specified
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CONFIG_UNUSED_KSYMS_WHITELIST="my/own/white/list" before enabling
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CONFIG_LTO_CLANG.
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So, the user-supplied whitelist and LTO-specific white list must be
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independent of each other.
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I refactored the shell script so CONFIG_MODVERSIONS and CONFIG_CLANG_LTO
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handle whitelists in the same way.
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Fixes: fbe078d397b4 ("kbuild: lto: add a default list of used symbols")
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Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
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---
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init/Kconfig | 1 -
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scripts/gen_autoksyms.sh | 33 ++++++++++++++++++++++++---------
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scripts/lto-used-symbollist.txt | 5 -----
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3 files changed, 24 insertions(+), 15 deletions(-)
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delete mode 100644 scripts/lto-used-symbollist.txt
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+
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+ksym_wl=
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if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then
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# Use 'eval' to expand the whitelist path and check if it is relative
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eval ksym_wl="$CONFIG_UNUSED_KSYMS_WHITELIST"
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@@ -40,16 +57,14 @@ cat > "$output_file" << EOT
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EOT
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[ -f modules.order ] && modlist=modules.order || modlist=/dev/null
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-sed 's/ko$/mod/' $modlist |
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-xargs -n1 sed -n -e '2{s/ /\n/g;/^$/!p;}' -- |
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-cat - "$ksym_wl" |
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+
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+{
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+ sed 's/ko$/mod/' $modlist | xargs -n1 sed -n -e '2p'
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+ echo "$needed_symbols"
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+ [ -n "$ksym_wl" ] && cat "$ksym_wl"
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+} | sed -e 's/ /\n/g' | sed -n -e '/^$/!p' |
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# Remove the dot prefix for ppc64; symbol names with a dot (.) hold entry
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# point addresses.
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sed -e 's/^\.//' |
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sort -u |
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sed -e 's/\(.*\)/#define __KSYM_1円 1/' >> "$output_file"
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-
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-# Special case for modversions (see modpost.c)
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-if [ -n "$CONFIG_MODVERSIONS" ]; then
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- echo "#define __KSYM_module_layout 1" >> "$output_file"
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-fi
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diff --git a/scripts/lto-used-symbollist.txt b/scripts/lto-used-symbollist.txt
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deleted file mode 100644
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index 38e7bb9ebaae..000000000000
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--- a/scripts/lto-used-symbollist.txt
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+++ /dev/null
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@@ -1,5 +0,0 @@
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-memcpy
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-memmove
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-memset
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-__stack_chk_fail
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-__stack_chk_guard
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--
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2.27.0
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diff --git a/init/Kconfig b/init/Kconfig
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index 0bf5b340b80e..351161326e3c 100644
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--- a/init/Kconfig
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+++ b/init/Kconfig
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@@ -2277,7 +2277,6 @@ config TRIM_UNUSED_KSYMS
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config UNUSED_KSYMS_WHITELIST
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string "Whitelist of symbols to keep in ksymtab"
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depends on TRIM_UNUSED_KSYMS
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- default "scripts/lto-used-symbollist.txt" if LTO_CLANG
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help
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By default, all unused exported symbols will be un-exported from the
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build when TRIM_UNUSED_KSYMS is selected.
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diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh
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index d54dfba15bf2..b74d5949fea6 100755
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--- a/scripts/gen_autoksyms.sh
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+++ b/scripts/gen_autoksyms.sh
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@@ -19,7 +19,24 @@ esac
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# We need access to CONFIG_ symbols
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. include/config/auto.conf
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-ksym_wl=/dev/null
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+needed_symbols=
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+
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+# Special case for modversions (see modpost.c)
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+if [ -n "$CONFIG_MODVERSIONS" ]; then
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+ needed_symbols="$needed_symbols module_layout"
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+fi
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+
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+# With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a binary
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+# when the .mod files are generated, which means they don't yet contain
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+# references to certain symbols that will be present in the final binaries.
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+if [ -n "$CONFIG_LTO_CLANG" ]; then
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+ # intrinsic functions
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+ needed_symbols="$needed_symbols memcpy memmove memset"
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+ # stack protector symbols
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+ needed_symbols="$needed_symbols __stack_chk_fail __stack_chk_guard"
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+fi
Thank you for the patch!
Arnd just reported that _mcount is also needed with some
configurations. Would you mind including that in the next version?
https://lore.kernel.org/r/20210225143456.3829513-1-arnd@xxxxxxxxxx/
Sami