[PATCH v1] selftests: Enhance kselftest_harness.h to print which assert failed

[MickaÃl SalaÃn]

When a test process is not able to write to TH_LOG_STREAM, this step
mechanism enable to print the assert number which triggered the failure.
This can be enabled by setting _metadata->no_print to true at the
beginning of the test sequence.

Update the seccomp-bpf test to return 0 if a test succeeded.

This feature is needed for the Landlock tests.

Signed-off-by: MickaÃl SalaÃn <mic@xxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Will Drewry <wad@xxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/CAGXu5j+D-FP8Kt9unNOqKrQJP4DYTpmgkJxWykZyrYiVPz3Y3Q@xxxxxxxxxxxxxx
---

Changes since the patch from the Landlock series:
* add the step counter in assert/expect macros and use _metadata to
  enable the counter (suggested by Kees Cook)
* only count asserts
* add documentation
---
 tools/testing/selftests/kselftest_harness.h   | 39 +++++++++++++++++++++++----
 tools/testing/selftests/seccomp/seccomp_bpf.c |  2 +-
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index c56f72e07cd7..e81bd28bdd89 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -51,6 +51,9 @@
 #define __KSELFTEST_HARNESS_H
 
 #define _GNU_SOURCE
+#include <asm/types.h>
+#include <errno.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -84,6 +87,14 @@
  * E.g., #define TH_LOG_ENABLED 1
  *
  * If no definition is provided, logging is enabled by default.
+ *
+ * If there is no way to print an error message for the process running the
+ * test (e.g. not allowed to write to stderr), it is still possible to get the
+ * ASSERT_* number for which the test failed.  This behavior can be enabled by
+ * writing `_metadata->no_print = true;` before the check sequence that is
+ * unable to print.  When an error occur, instead of printing an error message
+ * and calling `abort(3)`, the test process call `_exit(2)` with the assert
+ * number as argument, which is then printed by the parent process.
  */
 #define TH_LOG(fmt, ...) do { \
 	if (TH_LOG_ENABLED) \
@@ -555,12 +566,18 @@
  * return while still providing an optional block to the API consumer.
  */
 #define OPTIONAL_HANDLER(_assert) \
-	for (; _metadata->trigger;  _metadata->trigger = __bail(_assert))
+	for (; _metadata->trigger; _metadata->trigger = \
+			__bail(_assert, _metadata->no_print, _metadata->step))
+
+#define __INC_STEP(_metadata) \
+	if (_metadata->passed && _metadata->step < 255) \
+		_metadata->step++;
 
 #define __EXPECT(_expected, _seen, _t, _assert) do { \
 	/* Avoid multiple evaluation of the cases */ \
 	__typeof__(_expected) __exp = (_expected); \
 	__typeof__(_seen) __seen = (_seen); \
+	if (_assert) __INC_STEP(_metadata); \
 	if (!(__exp _t __seen)) { \
 		unsigned long long __exp_print = (uintptr_t)__exp; \
 		unsigned long long __seen_print = (uintptr_t)__seen; \
@@ -576,6 +593,7 @@
 #define __EXPECT_STR(_expected, _seen, _t, _assert) do { \
 	const char *__exp = (_expected); \
 	const char *__seen = (_seen); \
+	if (_assert) __INC_STEP(_metadata); \
 	if (!(strcmp(__exp, __seen) _t 0))  { \
 		__TH_LOG("Expected '%s' %s '%s'.", __exp, #_t, __seen); \
 		_metadata->passed = 0; \
@@ -590,6 +608,8 @@ struct __test_metadata {
 	int termsig;
 	int passed;
 	int trigger; /* extra handler after the evaluation */
+	__u8 step;
+	bool no_print; /* manual trigger when TH_LOG_STREAM is not available */
 	struct __test_metadata *prev, *next;
 };
 
@@ -634,10 +654,13 @@ static inline void __register_test(struct __test_metadata *t)
 	}
 }
 
-static inline int __bail(int for_realz)
+static inline int __bail(int for_realz, bool no_print, __u8 step)
 {
-	if (for_realz)
+	if (for_realz) {
+		if (no_print)
+			_exit(step);
 		abort();
+	}
 	return 0;
 }
 
@@ -655,18 +678,24 @@ void __run_test(struct __test_metadata *t)
 		t->passed = 0;
 	} else if (child_pid == 0) {
 		t->fn(t);
-		_exit(t->passed);
+		/* return the step that failed or 0 */
+		_exit(t->passed ? 0 : t->step);
 	} else {
 		/* TODO(wad) add timeout support. */
 		waitpid(child_pid, &status, 0);
 		if (WIFEXITED(status)) {
-			t->passed = t->termsig == -1 ? WEXITSTATUS(status) : 0;
+			t->passed = t->termsig == -1 ? !WEXITSTATUS(status) : 0;
 			if (t->termsig != -1) {
 				fprintf(TH_LOG_STREAM,
 					"%s: Test exited normally "
 					"instead of by signal (code: %d)\n",
 					t->name,
 					WEXITSTATUS(status));
+			} else if (!t->passed) {
+				fprintf(TH_LOG_STREAM,
+					"%s: Test failed at step #%d\n",
+					t->name,
+					WEXITSTATUS(status));
 			}
 		} else if (WIFSIGNALED(status)) {
 			t->passed = 0;
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 73f5ea6778ce..4d6f92a9df6b 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -107,7 +107,7 @@ TEST(mode_strict_support)
 	ASSERT_EQ(0, ret) {
 		TH_LOG("Kernel does not support CONFIG_SECCOMP");
 	}
-	syscall(__NR_exit, 1);
+	syscall(__NR_exit, 0);
 }
 
 TEST_SIGNAL(mode_strict_cannot_call_prctl, SIGKILL)
-- 
2.13.3