From 3db1cfb91b9b2b7cf6c5564995c446567baa371a Mon Sep 17 00:00:00 2001

From: Song Liu <song@kernel.org>

Date: Fri, 3 Feb 2023 10:28:16 -0800

Subject: [PATCH 102/107] kpatch-build: support CONFIG_LTO_CLANG_THIN

Support CONFIG_LTO_CLANG_THIN with ld.lld --lto-obj-path option.

With CONFIG_LTO_CLANG_THIN, .o files are LLVM IR binary, so CDO doesn't

work on .o file. To solve this issue, we CDO the thinlto files generated

by the --lto-obj-path option. Clang LTO generates the thinlto files

after cross file inline, so they are good candidates for CDO. See [1] for

more discussions about this.

To achieve this, we need:

  1. kpatch-build to update kernel Makefile(s) so it generates thinlto

     files;

  2. kpatch-build and kpatch-cc to save the thinlto file properly;

  3. kpatch-build to feed these thinlto files to CDO;

  4. The user need to supply vmlinux.o, from which we generate the symtab

     file. We need this because GLOBAL symbols may be marked as LOCAL in

     LTO vmlinux;

[1] https://github.com/dynup/kpatch/issues/1320

Signed-off-by: Song Liu <song@kernel.org>

---

 kpatch-build/kpatch-build | 59 +++++++++++++++++++++++++++++++++------

 kpatch-build/kpatch-cc    | 18 ++++++++++++

 2 files changed, 68 insertions(+), 9 deletions(-)

diff --git a/kpatch-build/kpatch-build b/kpatch-build/kpatch-build

index 45e8b14..f712578 100755

--- a/kpatch-build/kpatch-build

+++ b/kpatch-build/kpatch-build

@@ -173,11 +173,11 @@ cleanup() {

 	# restore original vmlinux if it was overwritten by sourcedir build

 	[[ -e "$TEMPDIR/vmlinux" ]] && mv -f "$TEMPDIR/vmlinux" "$KERNEL_SRCDIR/"

-	# restore original link-vmlinux.sh if we updated it for the build

+	# restore any files that were modified for the build

 	[[ -e "$TEMPDIR/link-vmlinux.sh" ]] && mv -f "$TEMPDIR/link-vmlinux.sh" "$KERNEL_SRCDIR/scripts"

-

-	# restore original Makefile.modfinal if we updated it for the build

 	[[ -e "$TEMPDIR/Makefile.modfinal" ]] && mv -f "$TEMPDIR/Makefile.modfinal" "$KERNEL_SRCDIR/scripts"

+	[[ -e "$TEMPDIR/Makefile.build" ]] && mv -f "$TEMPDIR/Makefile.build" "$KERNEL_SRCDIR/scripts"

+	[[ -e "$TEMPDIR/Makefile" ]] && mv -f "$TEMPDIR/Makefile" "$KERNEL_SRCDIR"

 	[[ "$DEBUG" -eq 0 ]] && rm -rf "$TEMPDIR"

 	rm -rf "$RPMTOPDIR"

@@ -1054,6 +1054,23 @@ if [[ -n "$CONFIG_DEBUG_INFO_BTF" ]]; then

 	fi

 fi

+if [[ -n "$CONFIG_LTO_CLANG" ]]; then

+	[[ -n "$CONFIG_LTO_CLANG_THIN" ]] || die "Non-thin LTO is not supported. Please enable CONFIG_LTO_CLANG_THIN"

+

+	# This is a heuristic: use -x to check vmlinux vs. vmlinux.o

+	[[ -x "$VMLINUX" ]] && die "For kernel with CONFIG_LTO_CLANG, please supply vmlinux.o instead of vmlinux via -v|--vmlinux option."

+

+	# update Makefile so that ld.lld generate vmlinux.o.thinlto.o* files for vmlinux.o

+	cp -f "$KERNEL_SRCDIR/Makefile" "$TEMPDIR/Makefile" || die

+	sed -i "s/--thinlto-cache-dir=\$(extmod_prefix).thinlto-cache/--lto-obj-path=vmlinux.o.thinlto.o/g" "$KERNEL_SRCDIR"/Makefile

+

+	# update scripts/Makefile.build so that ld.lld generate XX.o.thinlto.o* files for modules

+	cp -f "$KERNEL_SRCDIR/scripts/Makefile.build" "$TEMPDIR/Makefile.build" || die

+	sed -i "s/\$(ld_flags)/\$(ld_flags) --lto-obj-path=\$@.thinlto.o/g" "$KERNEL_SRCDIR"/scripts/Makefile.build

+

+	export KPATCH_CC_LTO=1

+fi

+

 if [[ -n "$CONFIG_CC_IS_CLANG" ]]; then

 	echo "WARNING: Clang support is experimental"

 fi

@@ -1174,9 +1191,14 @@ if [[ -n "$CONFIG_MODVERSIONS" ]]; then

 	trace_on

 fi

+if [[ -n "$CONFIG_LTO_CLANG" ]]; then

+	DIFF_OBJS="$TEMPDIR/thinlto_objs"

+else

+	DIFF_OBJS="$TEMPDIR/changed_objs"

+fi

 # Read as words, no quotes.

 # shellcheck disable=SC2013

-for i in $(cat "$TEMPDIR/changed_objs")

+for i in $(cat "$DIFF_OBJS")

 do

 	mkdir -p "$TEMPDIR/patched/$(dirname "$i")" || die

 	cp -f "$BUILDDIR/$i" "$TEMPDIR/patched/$i" || die

@@ -1205,7 +1227,8 @@ if [[ -z "$MODNAME" ]] ; then

 	MODNAME="$(module_name_string "$MODNAME")"

 fi

-FILES="$(cat "$TEMPDIR/changed_objs")"

+FILES="$(cat "$DIFF_OBJS")"

+

 cd "$TEMPDIR" || die

 mkdir output

 declare -a objnames

@@ -1229,7 +1252,11 @@ for i in $FILES; do

 	mkdir -p "output/$(dirname "$i")"

 	cd "$BUILDDIR" || die

-	find_kobj "$i"

+	if [[ -n "$CONFIG_LTO_CLANG" ]] ; then

+		KOBJFILE=${i/.o.thinlto.o*/}

+	else

+		find_kobj "$i"

+	fi

 	cd "$TEMPDIR" || die

 	if [[ -e "orig/$i" ]]; then

 		if [[ -n $OOT_MODULE ]]; then

@@ -1246,16 +1273,30 @@ for i in $FILES; do

 		else

 			KOBJFILE_NAME=$(basename "${KOBJFILE%.ko}")

 			KOBJFILE_NAME="${KOBJFILE_NAME//-/_}"

-			KOBJFILE_PATH="${TEMPDIR}/module/$KOBJFILE"

+			if [[ -n "$CONFIG_LTO_CLANG" ]] ; then

+				KOBJFILE_PATH="${TEMPDIR}/module/$KOBJFILE.ko"

+			else

+				KOBJFILE_PATH="${TEMPDIR}/module/$KOBJFILE"

+			fi

 			SYMTAB="${KOBJFILE_PATH}.symtab"

 			SYMVERS_FILE="$BUILDDIR/Module.symvers"

 		fi

-		"$READELF" -s --wide "$KOBJFILE_PATH" > "$SYMTAB"

+		# With CONFIG_LTO_CLANG, multiple .thinlto files share a

+		# symtab file. Only generate the symtab file once.

+		[[ -e "$SYMTAB" ]] || "$READELF" --symbols --wide "$KOBJFILE_PATH" > "$SYMTAB"

 		if [[ "$ARCH" = "ppc64le" ]]; then

 			sed -ri 's/\s+\[<localentry>: 8\]//' "$SYMTAB"

 		fi

+		if [[ -n "$CONFIG_LTO_CLANG" ]] ; then

+			# skip .thinlto file that didn't change at all

+			diff "orig/$i" "patched/$i" 2> /dev/null && continue

+			# skip .thinlto file without any functions

+			num_func=$("$READELF" --symbols "orig/$i" | grep -c FUNC)

+			[[ $num_func -eq 0 ]] && continue

+		fi

+

 		# create-diff-object orig.o patched.o parent-name parent-symtab

 		#		     Module.symvers patch-mod-name output.o

 		"$TOOLSDIR"/create-diff-object $CDO_FLAGS "orig/$i" "patched/$i" "$KOBJFILE_NAME" \

@@ -1308,7 +1349,7 @@ fi

 cd "$TEMPDIR/output" || die

 # $KPATCH_LDFLAGS and result of find used as list, no quotes.

 # shellcheck disable=SC2086,SC2046

-"$LD" -r $KPATCH_LDFLAGS -o ../patch/tmp_output.o $(find . -name "*.o") 2>&1 | logger || die

+"$LD" -r $KPATCH_LDFLAGS -o ../patch/tmp_output.o $(find . -name "*.o*") 2>&1 | logger || die

 if [[ "$USE_KLP" -eq 1 ]]; then

 	cp -f "$TEMPDIR"/patch/tmp_output.o "$TEMPDIR"/patch/output.o || die

diff --git a/kpatch-build/kpatch-cc b/kpatch-build/kpatch-cc

index 2a3d264..7e9e1be 100755

--- a/kpatch-build/kpatch-cc

+++ b/kpatch-build/kpatch-cc

@@ -79,6 +79,24 @@ elif [[ "$TOOLCHAINCMD" =~ ^(.*-)?ld || "$TOOLCHAINCMD" =~ ^(.*-)?ld.lld ]] ; th

 					args+=(--warn-unresolved-symbols)

 					break

 					;;

+				*/.tmp_*.o)

+					# .tmp_*.o is used for single file modules.

+					# See "cmd_ld_single_m" in scripts/Makefile.build.

+					if [[ $KPATCH_CC_LTO -eq 1 ]] ; then

+						mkdir -p "$KPATCH_GCC_TEMPDIR/orig/$(dirname "$relobj")"

+						cp "${obj/.tmp_/}".thinlto.o* "$KPATCH_GCC_TEMPDIR/orig/$(dirname "$relobj")"

+						echo "${obj/.tmp_/}".thinlto.o* >> "$KPATCH_GCC_TEMPDIR/thinlto_objs"

+					fi

+					break

+					;;

+				*.o)

+					if [[ $KPATCH_CC_LTO -eq 1 ]] ; then

+						mkdir -p "$KPATCH_GCC_TEMPDIR/orig/$(dirname "$relobj")"

+						cp "$obj".thinlto* "$KPATCH_GCC_TEMPDIR/orig/$(dirname "$relobj")"

+						echo "$obj".thinlto.o* >> "$KPATCH_GCC_TEMPDIR/thinlto_objs"

+					fi

+					break

+					;;

 				*)

 					break

 					;;

-- 

2.37.3