[PATCH 19/48] klp-build: Fix checksum comparison for changed offsets

Josh Poimboeuf
2026-04-23T04:04:33Z

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")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
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 81b35fc10877..2b8b3c338a87 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=$'\t' read -r orig patched; do
+ read -ra orig <<< "$orig"
+ read -ra patched <<< "$patched"
+
+ 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
}
--
2.53.0