[tip: objtool/core] klp-build: Fix checksum comparison for changed offsets

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     ba77fe55781a2464f68b6c13b4b31d05abd2abcf
Gitweb:        https://git.kernel.org/tip/ba77fe55781a2464f68b6c13b4b31d05abd2abcf
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Fri, 10 Apr 2026 21:49:56 -07:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Mon, 04 May 2026 21:16:02 -07:00

klp-build: Fix checksum comparison for changed offsets

The klp-build -f/--show-first-changed feature uses diff to compare
checksum log lines between original and patched objects.  However, diff
compares entire lines, including the offset field.  When a function is
at a different section offset, the offset field differs even though the
instruction checksum is identical, causing the wrong instruction to be
printed.

Only compare the checksum field when looking for the first changed
instruction.  Also print both the original and patched offsets when they
differ.

Fixes: 78be9facfb5e ("livepatch/klp-build: Add --show-first-changed option to show function divergence")
Acked-by: Song Liu <song@xxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 scripts/livepatch/klp-build | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index e19d93b..8f0ea56 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -727,13 +727,29 @@ diff_checksums() {
 		)
 
 		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
+			local -a orig patched
+			paste <(grep0 -E "^DEBUG: .*checksum: $func " "$orig_log") \
+			      <(grep0 -E "^DEBUG: .*checksum: $func " "$patched_log") |
+			while IFS= read -r line; do
+				read -ra orig <<< "${line%%$'\t'*}"
+				read -ra patched <<< "${line#*$'\t'}"
+
+				if [[ ${#patched[@]} -eq 0 ]]; then
+					printf "%s: %s: %s (removed)\n" "${orig[1]%:}" "${orig[3]}" "${orig[-2]}"
+					break
+				elif [[ ${#orig[@]} -eq 0 ]]; then
+					printf "%s: %s: %s (added)\n" "${patched[1]%:}" "${patched[3]}" "${patched[-2]}"
+					break
+				fi
+
+				[[ "${orig[-1]}" == "${patched[-1]}" ]] && continue
+
+				printf "%s: %s: %s" "${orig[1]%:}" "${orig[3]}" "${orig[-2]}"
+				[[ "${orig[-2]}" != "${patched[-2]}" ]] && \
+					printf " (patched: %s)" "${patched[-2]}"
+				printf "\n"
+				break
+			done || true
 		done
 	done
 }