[PATCH v2 07/12] selftests/livepatch: Test klp-prepare-patch with patches which cancel out

[Song Liu <song@kernel.org>]

Add a test where a patch is followed by its revert.  On their own the
two leave nothing to build, so klp-prepare-patch fails with "no changes
detected", and klp-build stops before building anything.  With another
patch after them, only that patch's change is left in the combined
patch.

Add expect_error() to functions.sh to check for a failure with a given
error message.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@kernel.org>
---
 .../livepatch/test_klp_build/Makefile         |   3 +-
 .../livepatch/test_klp_build/functions.sh     |  14 +++
 .../test_klp_build/test-cancelling-patches.sh | 102 ++++++++++++++++++
 3 files changed, 118 insertions(+), 1 deletion(-)
 create mode 100755 tools/testing/selftests/livepatch/test_klp_build/test-cancelling-patches.sh

diff --git a/tools/testing/selftests/livepatch/test_klp_build/Makefile b/tools/testing/selftests/livepatch/test_klp_build/Makefile
index 50205a047dcd..158a08d8a1b8 100644
--- a/tools/testing/selftests/livepatch/test_klp_build/Makefile
+++ b/tools/testing/selftests/livepatch/test_klp_build/Makefile
@@ -2,7 +2,8 @@
 
 TEST_PROGS := \
 	test-basic.sh \
-	test-independent-patches.sh
+	test-independent-patches.sh \
+	test-cancelling-patches.sh
 
 TEST_PROGS_EXTENDED := functions.sh
 
diff --git a/tools/testing/selftests/livepatch/test_klp_build/functions.sh b/tools/testing/selftests/livepatch/test_klp_build/functions.sh
index 6b2f30d72f99..e28988d07bc9 100644
--- a/tools/testing/selftests/livepatch/test_klp_build/functions.sh
+++ b/tools/testing/selftests/livepatch/test_klp_build/functions.sh
@@ -133,3 +133,17 @@ function expect_patch() {
 
 	echo "ok"
 }
+
+# expect_error(msg) - check that klp-prepare-patch failed with an error message
+#	msg - the message, without the "error: klp-prepare-patch: " prefix
+function expect_error() {
+	[[ $STATUS -ne 0 ]] ||
+		not_ok "klp-prepare-patch succeeded unexpectedly:" "$WORK_DIR/stdout"
+	[[ -s "$WORK_DIR/stdout" ]] &&
+		not_ok "klp-prepare-patch printed a patch:" "$WORK_DIR/stdout"
+
+	grep -qxF "error: klp-prepare-patch: $1" "$WORK_DIR/stderr" ||
+		not_ok "klp-prepare-patch didn't fail with \"$1\":" "$WORK_DIR/stderr"
+
+	echo "ok"
+}
diff --git a/tools/testing/selftests/livepatch/test_klp_build/test-cancelling-patches.sh b/tools/testing/selftests/livepatch/test_klp_build/test-cancelling-patches.sh
new file mode 100755
index 000000000000..da6a12064be9
--- /dev/null
+++ b/tools/testing/selftests/livepatch/test_klp_build/test-cancelling-patches.sh
@@ -0,0 +1,102 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+. "$(dirname "$0")/functions.sh"
+
+setup_tree
+
+add_file drivers/foo/foo.c <<'EOT'
+int foo(int x)
+{
+	if (x < 0)
+		return -1;
+	return x;
+}
+
+int bar(void)
+{
+	return __LINE__;
+}
+
+int baz(int x)
+{
+	if (x > 100)
+		return 100;
+	return x;
+}
+EOT
+
+add_patch 0001-foo.patch <<'EOT'
+--- a/drivers/foo/foo.c
++++ b/drivers/foo/foo.c
+@@ -1,6 +1,8 @@
+ int foo(int x)
+ {
++	if (!x)
++		return 0;
+ 	if (x < 0)
+ 		return -1;
+ 	return x;
+ }
+EOT
+
+add_patch 0002-revert-foo.patch <<'EOT'
+--- a/drivers/foo/foo.c
++++ b/drivers/foo/foo.c
+@@ -1,8 +1,6 @@
+ int foo(int x)
+ {
+-	if (!x)
+-		return 0;
+ 	if (x < 0)
+ 		return -1;
+ 	return x;
+ }
+EOT
+
+add_patch 0003-baz.patch <<'EOT'
+--- a/drivers/foo/foo.c
++++ b/drivers/foo/foo.c
+@@ -12,7 +12,7 @@ int bar(void)
+
+ int baz(int x)
+ {
+-	if (x > 100)
+-		return 100;
++	if (x > 1000)
++		return 1000;
+ 	return x;
+ }
+EOT
+
+# - a patch and its revert leave nothing to build
+
+start_test "patch and its revert"
+
+run_klp_prepare_patch 0001-foo.patch 0002-revert-foo.patch
+
+expect_error "no changes detected"
+
+# - with another patch after them, only that patch's change is left
+
+start_test "patch and its revert, then another patch"
+
+run_klp_prepare_patch 0001-foo.patch 0002-revert-foo.patch 0003-baz.patch
+
+expect_patch <<'EOT'
+--- a/drivers/foo/foo.c
++++ b/drivers/foo/foo.c
+@@ -12,7 +12,8 @@ int bar(void)
+
+ int baz(int x)
+ {
+-	if (x > 100)
+-		return 100;
++	if (x > 1000)
++		return 1000;
++#line 17
+ 	return x;
+ }
+EOT
+
+exit 0
-- 
2.53.0-Meta