From 909d7a656bb5e638bb199b8abd1c5b221b873793 Mon Sep 17 00:00:00 2001

From: Song Liu <songliubraving@fb.com>

Date: Wed, 13 Oct 2021 00:10:20 -0700

Subject: [PATCH 1/2] create-diff-object: compare section name with

 kpatch_section_function_name

Profile-Guided Optimization (PGO) uses profiling data to help the compiler

to evaluate the properties of a function, and thus adds different prefixes

to the section/function. For example, with -ffunction-sections, the

compiler will prefix some sectiones with .text.unlikely. However, if a

function changes from the version in the profiling data, the compiler may

ignore the profiling data. This often happens to the patched function

when kpatch-build builds the patch. As a result, the original function

and the patch function may have different prefix, i.e., one of them has

.text, the other has .text.unlikely.

To correlate these functions properly, use kpatch_section_function_name()

in kpatch_correlate_sections() to find matching sections.

Signed-off-by: Song Liu <songliubraving@fb.com>

---

 kpatch-build/create-diff-object.c | 7 +++++--

 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c

index 826741d0..319ed68d 100644

--- a/kpatch-build/create-diff-object.c

+++ b/kpatch-build/create-diff-object.c

@@ -1001,6 +1001,8 @@ static void kpatch_correlate_section(struct section *sec_orig,

 		kpatch_correlate_symbol(sec_orig->sym, sec_patched->sym);

 }

+static char *kpatch_section_function_name(struct section *sec);

+

 static void kpatch_correlate_sections(struct list_head *seclist_orig,

 		struct list_head *seclist_patched)

 {

@@ -1010,8 +1012,9 @@ static void kpatch_correlate_sections(struct list_head *seclist_orig,

 		if (sec_orig->twin)

 			continue;

 		list_for_each_entry(sec_patched, seclist_patched, list) {

-			if (kpatch_mangled_strcmp(sec_orig->name, sec_patched->name) ||

-			    sec_patched->twin)

+			if (sec_patched->twin ||

+			    kpatch_mangled_strcmp(kpatch_section_function_name(sec_orig),

+						  kpatch_section_function_name(sec_patched)))

 				continue;

 			if (is_special_static(is_rela_section(sec_orig) ?

From 0223fa3ab3efc1bed18cff7acf470185e2e66406 Mon Sep 17 00:00:00 2001

From: Song Liu <songliubraving@fb.com>

Date: Wed, 13 Oct 2021 01:03:55 -0700

Subject: [PATCH 2/2] kpatch-build: add support for clang pgo

For clang with Profile-Guided Optimization (PGO), profile data is needed

to compile the livepatch properly. Add option -p|--profile-data, which

specifies the profile data file. This option is only valid with

CONFIG_CC_IS_CLANG and CONFIG_PGO_CLANG.

Signed-off-by: Song Liu <songliubraving@fb.com>

---

 kpatch-build/kpatch-build | 20 +++++++++++++++++++-

 1 file changed, 19 insertions(+), 1 deletion(-)

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

index 634095d5..1f3fc99b 100755

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

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

@@ -535,9 +535,10 @@ usage() {

 	echo "		--skip-cleanup          Skip post-build cleanup" >&2

 	echo "		--skip-compiler-check   Skip compiler version matching check" >&2

 	echo "		                        (not recommended)" >&2

+	echo "		-p, --profile-data      specify profile data for PGO (clang only)" >&2

 }

-options="$(getopt -o ha:r:s:c:v:j:t:n:o:dR -l "help,archversion:,sourcerpm:,sourcedir:,config:,vmlinux:,jobs:,target:,name:,output:,oot-module:,oot-module-src:,debug,skip-gcc-check,skip-compiler-check,skip-cleanup,non-replace" -- "$@")" || die "getopt failed"

+options="$(getopt -o ha:r:s:c:v:j:t:n:o:dRp: -l "help,archversion:,sourcerpm:,sourcedir:,config:,vmlinux:,jobs:,target:,name:,output:,oot-module:,oot-module-src:,debug,skip-gcc-check,skip-compiler-check,skip-cleanup,non-replace,profile-data" -- "$@")" || die "getopt failed"

 eval set -- "$options"

@@ -619,6 +620,10 @@ while [[ $# -gt 0 ]]; do

 		echo "WARNING: Skipping compiler version matching check (not recommended)"

 		SKIPCOMPILERCHECK=1

 		;;

+	-p|--profile-data)

+		PROFILE_DATA="$(readlink -f "$2")"

+		shift

+		;;

 	*)

 		[[ "$1" = "--" ]] && shift && continue

 		[[ ! -f "$1" ]] && die "patch file '$1' not found"

@@ -896,6 +901,16 @@ fi

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

 	echo "WARNING: Clang support is experimental"

+	if [[ -z "$PROFILE_DATA" ]] && [[ -n "$CONFIG_PGO_CLANG" ]]; then

+		die "Please specify profile-data for CONFIG_PGO_CLANG"

+	fi

+	if [[ -n "$PROFILE_DATA" ]] && [[ -z "$CONFIG_PGO_CLANG" ]]; then

+		echo "WARNING profile-data specified w/o CONFIG_PGO_CLANG, ignore it"

+	fi

+else

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

+		die "Only supports profile-data with Clang"

+	fi

 fi

 if [[ "$SKIPCOMPILERCHECK" -eq 0 ]]; then

@@ -943,6 +958,9 @@ declare -a MAKEVARS

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

 	MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${CLANG}")

 	MAKEVARS+=("HOSTCC=clang")

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

+		MAKEVARS+=("CFLAGS_PGO_CLANG=-fprofile-use=$PROFILE_DATA")

+	fi

 else

 	MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${GCC}")

 fi