selftests: harness: Add kselftest harness selftest

Add a selftest for the kselftest harness itself so any changes can be
validated.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250505-nolibc-kselftest-harness-v4-1-ee4dd5257135@linutronix.de
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

7 files changed, 224 insertions, 0 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 96b827049501..9d5278df33c8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21742,6 +21742,7 @@ F:	include/linux/seccomp.h
 F:	include/uapi/linux/seccomp.h
 F:	kernel/seccomp.c
 F:	tools/testing/selftests/kselftest_harness.h
+F:	tools/testing/selftests/kselftest_harness/
 F:	tools/testing/selftests/seccomp/*
 K:	\bsecure_computing
 K:	\bTIF_SECCOMP\b
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index c77c8c8e3d9b..27592909a596 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -48,6 +48,7 @@ TARGETS += ipc
 TARGETS += ir
 TARGETS += kcmp
 TARGETS += kexec
+TARGETS += kselftest_harness
 TARGETS += kvm
 TARGETS += landlock
 TARGETS += lib
diff --git a/tools/testing/selftests/kselftest_harness/.gitignore b/tools/testing/selftests/kselftest_harness/.gitignore
new file mode 100644
index 000000000000..e4e476a333c9
--- /dev/null
+++ b/tools/testing/selftests/kselftest_harness/.gitignore
@@ -0,0 +1,2 @@
+/harness-selftest
+/harness-selftest.seen
diff --git a/tools/testing/selftests/kselftest_harness/Makefile b/tools/testing/selftests/kselftest_harness/Makefile
new file mode 100644
index 000000000000..0617535a6ce4
--- /dev/null
+++ b/tools/testing/selftests/kselftest_harness/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0
+
+TEST_GEN_PROGS_EXTENDED := harness-selftest
+TEST_PROGS := harness-selftest.sh
+EXTRA_CLEAN := harness-selftest.seen
+
+include ../lib.mk
diff --git a/tools/testing/selftests/kselftest_harness/harness-selftest.c b/tools/testing/selftests/kselftest_harness/harness-selftest.c
new file mode 100644
index 000000000000..b555493bdb4d
--- /dev/null
+++ b/tools/testing/selftests/kselftest_harness/harness-selftest.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <stdio.h>
+
+#include <sys/resource.h>
+#include <sys/prctl.h>
+
+/* Avoid any inconsistencies */
+#define TH_LOG_STREAM stdout
+
+#include "../kselftest_harness.h"
+
+static void test_helper(struct __test_metadata *_metadata)
+{
+	ASSERT_EQ(0, 0);
+}
+
+TEST(standalone_pass) {
+	TH_LOG("before");
+	ASSERT_EQ(0, 0);
+	EXPECT_EQ(0, 0);
+	test_helper(_metadata);
+	TH_LOG("after");
+}
+
+TEST(standalone_fail) {
+	TH_LOG("before");
+	EXPECT_EQ(0, 0);
+	EXPECT_EQ(0, 1);
+	ASSERT_EQ(0, 1);
+	TH_LOG("after");
+}
+
+TEST_SIGNAL(signal_pass, SIGUSR1) {
+	TH_LOG("before");
+	ASSERT_EQ(0, 0);
+	TH_LOG("after");
+	kill(getpid(), SIGUSR1);
+}
+
+TEST_SIGNAL(signal_fail, SIGUSR1) {
+	TH_LOG("before");
+	ASSERT_EQ(0, 1);
+	TH_LOG("after");
+	kill(getpid(), SIGUSR1);
+}
+
+FIXTURE(fixture) {
+	pid_t testpid;
+};
+
+FIXTURE_SETUP(fixture) {
+	TH_LOG("setup");
+	self->testpid = getpid();
+}
+
+FIXTURE_TEARDOWN(fixture) {
+	TH_LOG("teardown same-process=%d", self->testpid == getpid());
+}
+
+TEST_F(fixture, pass) {
+	TH_LOG("before");
+	ASSERT_EQ(0, 0);
+	test_helper(_metadata);
+	standalone_pass(_metadata);
+	TH_LOG("after");
+}
+
+TEST_F(fixture, fail) {
+	TH_LOG("before");
+	ASSERT_EQ(0, 1);
+	fixture_pass(_metadata, self, variant);
+	TH_LOG("after");
+}
+
+TEST_F_TIMEOUT(fixture, timeout, 1) {
+	TH_LOG("before");
+	sleep(2);
+	TH_LOG("after");
+}
+
+FIXTURE(fixture_parent) {
+	pid_t testpid;
+};
+
+FIXTURE_SETUP(fixture_parent) {
+	TH_LOG("setup");
+	self->testpid = getpid();
+}
+
+FIXTURE_TEARDOWN_PARENT(fixture_parent) {
+	TH_LOG("teardown same-process=%d", self->testpid == getpid());
+}
+
+TEST_F(fixture_parent, pass) {
+	TH_LOG("before");
+	ASSERT_EQ(0, 0);
+	TH_LOG("after");
+}
+
+FIXTURE(fixture_setup_failure) {
+	pid_t testpid;
+};
+
+FIXTURE_SETUP(fixture_setup_failure) {
+	TH_LOG("setup");
+	self->testpid = getpid();
+	ASSERT_EQ(0, 1);
+}
+
+FIXTURE_TEARDOWN(fixture_setup_failure) {
+	TH_LOG("teardown same-process=%d", self->testpid == getpid());
+}
+
+TEST_F(fixture_setup_failure, pass) {
+	TH_LOG("before");
+	ASSERT_EQ(0, 0);
+	TH_LOG("after");
+}
+
+int main(int argc, char **argv)
+{
+	/*
+	 * The harness uses abort() to signal assertion failures, which triggers coredumps.
+	 * This may be useful to debug real failures but not for this selftest, disable them.
+	 */
+	struct rlimit rlimit = {
+		.rlim_cur = 0,
+		.rlim_max = 0,
+	};
+
+	prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
+	setrlimit(RLIMIT_CORE, &rlimit);
+
+	return test_harness_run(argc, argv);
+}
diff --git a/tools/testing/selftests/kselftest_harness/harness-selftest.expected b/tools/testing/selftests/kselftest_harness/harness-selftest.expected
new file mode 100644
index 000000000000..97e1418c1c7e
--- /dev/null
+++ b/tools/testing/selftests/kselftest_harness/harness-selftest.expected
@@ -0,0 +1,64 @@
+TAP version 13
+1..9
+# Starting 9 tests from 4 test cases.
+#  RUN           global.standalone_pass ...
+# harness-selftest.c:19:standalone_pass:before
+# harness-selftest.c:23:standalone_pass:after
+#            OK  global.standalone_pass
+ok 1 global.standalone_pass
+#  RUN           global.standalone_fail ...
+# harness-selftest.c:27:standalone_fail:before
+# harness-selftest.c:29:standalone_fail:Expected 0 (0) == 1 (1)
+# harness-selftest.c:30:standalone_fail:Expected 0 (0) == 1 (1)
+# standalone_fail: Test terminated by assertion
+#          FAIL  global.standalone_fail
+not ok 2 global.standalone_fail
+#  RUN           global.signal_pass ...
+# harness-selftest.c:35:signal_pass:before
+# harness-selftest.c:37:signal_pass:after
+#            OK  global.signal_pass
+ok 3 global.signal_pass
+#  RUN           global.signal_fail ...
+# harness-selftest.c:42:signal_fail:before
+# harness-selftest.c:43:signal_fail:Expected 0 (0) == 1 (1)
+# signal_fail: Test terminated by assertion
+#          FAIL  global.signal_fail
+not ok 4 global.signal_fail
+#  RUN           fixture.pass ...
+# harness-selftest.c:53:pass:setup
+# harness-selftest.c:62:pass:before
+# harness-selftest.c:19:pass:before
+# harness-selftest.c:23:pass:after
+# harness-selftest.c:66:pass:after
+# harness-selftest.c:58:pass:teardown same-process=1
+#            OK  fixture.pass
+ok 5 fixture.pass
+#  RUN           fixture.fail ...
+# harness-selftest.c:53:fail:setup
+# harness-selftest.c:70:fail:before
+# harness-selftest.c:71:fail:Expected 0 (0) == 1 (1)
+# harness-selftest.c:58:fail:teardown same-process=1
+# fail: Test terminated by assertion
+#          FAIL  fixture.fail
+not ok 6 fixture.fail
+#  RUN           fixture.timeout ...
+# harness-selftest.c:53:timeout:setup
+# harness-selftest.c:77:timeout:before
+# timeout: Test terminated by timeout
+#          FAIL  fixture.timeout
+not ok 7 fixture.timeout
+#  RUN           fixture_parent.pass ...
+# harness-selftest.c:87:pass:setup
+# harness-selftest.c:96:pass:before
+# harness-selftest.c:98:pass:after
+# harness-selftest.c:92:pass:teardown same-process=0
+#            OK  fixture_parent.pass
+ok 8 fixture_parent.pass
+#  RUN           fixture_setup_failure.pass ...
+# harness-selftest.c:106:pass:setup
+# harness-selftest.c:108:pass:Expected 0 (0) == 1 (1)
+# pass: Test terminated by assertion
+#          FAIL  fixture_setup_failure.pass
+not ok 9 fixture_setup_failure.pass
+# FAILED: 4 / 9 tests passed.
+# Totals: pass:4 fail:5 xfail:0 xpass:0 skip:0 error:0
diff --git a/tools/testing/selftests/kselftest_harness/harness-selftest.sh b/tools/testing/selftests/kselftest_harness/harness-selftest.sh
new file mode 100755
index 000000000000..fe72d16370fe
--- /dev/null
+++ b/tools/testing/selftests/kselftest_harness/harness-selftest.sh
@@ -0,0 +1,13 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Selftest for kselftest_harness.h
+#
+
+set -e
+
+DIR="$(dirname $(readlink -f "$0"))"
+
+"$DIR"/harness-selftest > harness-selftest.seen || true
+
+diff -u "$DIR"/harness-selftest.expected harness-selftest.seen