Commit 78be9fac authored by Josh Poimboeuf's avatar Josh Poimboeuf
Browse files

livepatch/klp-build: Add --show-first-changed option to show function divergence 



Add a --show-first-changed option to identify where changed functions
begin to diverge:

  - Parse 'objtool klp diff' output to find changed functions.

  - Run objtool again on each object with --debug-checksum=<funcs>.

  - Diff the per-instruction checksum debug output to locate the first
    differing instruction.

This can be useful for quickly determining where and why a function
changed.

Acked-by: default avatarPetr Mladek <pmladek@suse.com>
Tested-by: default avatarJoe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
parent 2c2f0b86

scripts/livepatch/klp-build

+78 −4
Original line number Diff line number Diff line
@@ -20,7 +20,7 @@ set -o nounset 
# This helps keep execution in pipes so pipefail+errexit can catch errors.

shopt -s lastpipe



unset DEBUG_CLONE SKIP_CLEANUP XTRACE

unset DEBUG_CLONE DIFF_CHECKSUM SKIP_CLEANUP XTRACE



REPLACE=1

SHORT_CIRCUIT=0
@@ -114,6 +114,7 @@ Usage: $SCRIPT [OPTIONS] PATCH_FILE(s) 
Generate a livepatch module.



Options:

   -f, --show-first-changed	Show address of first changed instruction

   -j, --jobs=<jobs>		Build jobs to run simultaneously [default: $JOBS]

   -o, --output=<file.ko>	Output file [default: livepatch-<patch-name>.ko]

       --no-replace		Disable livepatch atomic replace
@@ -141,8 +142,8 @@ process_args() { 
	local long

	local args



	short="hj:o:vdS:T"

	long="help,jobs:,output:,no-replace,verbose,debug,short-circuit:,keep-tmp"

	short="hfj:o:vdS:T"

	long="help,show-first-changed,jobs:,output:,no-replace,verbose,debug,short-circuit:,keep-tmp"



	args=$(getopt --options "$short" --longoptions "$long" -- "$@") || {

		echo; usage; exit
@@ -155,6 +156,10 @@ process_args() { 
				usage

				exit 0

				;;

			-f | --show-first-changed)

				DIFF_CHECKSUM=1

				shift

				;;

			-j | --jobs)

				JOBS="$2"

				shift 2
@@ -618,6 +623,7 @@ diff_objects() { 
		local orig_file="$rel_file"

		local patched_file="$PATCHED_DIR/$rel_file"

		local out_file="$DIFF_DIR/$rel_file"

		local filter=()

		local cmd=()



		mkdir -p "$(dirname "$out_file")"
@@ -630,16 +636,80 @@ diff_objects() { 
		cmd+=("$patched_file")

		cmd+=("$out_file")



		if [[ -v DIFF_CHECKSUM ]]; then

			filter=("grep0")

			filter+=("-Ev")

			filter+=("DEBUG: .*checksum: ")

		else

			filter=("cat")

		fi



		(

			cd "$ORIG_DIR"

			"${cmd[@]}"							\

				1> >(tee -a "$log")					\

				2> >(tee -a "$log" >&2) ||				\

				2> >(tee -a "$log" | "${filter[@]}" >&2) ||		\

				die "objtool klp diff failed"

		)

	done

}



# For each changed object, run objtool with --debug-checksum to get the

# per-instruction checksums, and then diff those to find the first changed

# instruction for each function.

diff_checksums() {

	local orig_log="$ORIG_DIR/checksum.log"

	local patched_log="$PATCHED_DIR/checksum.log"

	local -A funcs

	local cmd=()

	local line

	local file

	local func



	gawk '/\.o: changed function: / {

		sub(/:$/, "", $1)

		print $1, $NF

	}' "$KLP_DIFF_LOG" | mapfile -t lines



	for line in "${lines[@]}"; do

		read -r file func <<< "$line"

		if [[ ! -v funcs["$file"] ]]; then

			funcs["$file"]="$func"

		else

			funcs["$file"]+=" $func"

		fi

	done



	cmd=("$SRC/tools/objtool/objtool")

	cmd+=("--checksum")

	cmd+=("--link")

	cmd+=("--dry-run")



	for file in "${!funcs[@]}"; do

		local opt="--debug-checksum=${funcs[$file]// /,}"



		(

			cd "$ORIG_DIR"

			"${cmd[@]}" "$opt" "$file" &> "$orig_log" || \

				( cat "$orig_log" >&2; die "objtool --debug-checksum failed" )



			cd "$PATCHED_DIR"

			"${cmd[@]}" "$opt" "$file" &> "$patched_log" ||	\

				( cat "$patched_log" >&2; die "objtool --debug-checksum failed" )

		)



		for func in ${funcs[$file]}; do

			diff <( grep0 -E "^DEBUG: .*checksum: $func " "$orig_log"    | sed "s|$ORIG_DIR/||")	\

			     <( grep0 -E "^DEBUG: .*checksum: $func " "$patched_log" | sed "s|$PATCHED_DIR/||")	\

				| gawk '/^< DEBUG: / {

					gsub(/:/, "")

					printf "%s: %s: %s\n", $3, $5, $6

					exit

			}' || true

		done

	done

}



# Build and post-process livepatch module in $KMOD_DIR

build_patch_module() {

	local makefile="$KMOD_DIR/Kbuild"
@@ -743,6 +813,10 @@ fi 
if (( SHORT_CIRCUIT <= 3 )); then

	status "Diffing objects"

	diff_objects

	if [[ -v DIFF_CHECKSUM ]]; then

		status "Finding first changed instructions"

		diff_checksums

	fi

fi



if (( SHORT_CIRCUIT <= 4 )); then