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