[PATCH bpf-next 3/3] selftests/bpf: Skip compare_text subtest when stdout is not saved

[KaFai Wan <kafai.wan@linux.dev>]

stdio_hijack_init() does not set subtest_state->stdout_saved when
running with -v in non-parallel mode, since output goes straight to
stdout. In that case subtest_state->log_buf is left NULL, so the
compare_text_mismatch subtest crashes when inspecting it. Skip it when
stdout was not saved.

Fixes: bd71904697c6 ("selftests/bpf: Add compare_text_to_expected() helper")
Signed-off-by: KaFai Wan <kafai.wan@linux.dev>
---
 .../bpf/prog_tests/prog_tests_framework.c      | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/prog_tests_framework.c b/tools/testing/selftests/bpf/prog_tests/prog_tests_framework.c
index b4cd7c7ff439..ddb6cdc1579f 100644
--- a/tools/testing/selftests/bpf/prog_tests/prog_tests_framework.c
+++ b/tools/testing/selftests/bpf/prog_tests/prog_tests_framework.c
@@ -203,14 +203,18 @@ void test_prog_tests_framework_compare_text(void)
 	}
 
 	if (test__start_subtest("compare_text_mismatch")) {
-		err = compare_text_to_expected("line two\n", "line one\n");
-		fflush(stdout);
+		if (!env.subtest_state->stdout_saved) {
+			test__skip();
+		} else {
+			err = compare_text_to_expected("line two\n", "line one\n");
+			fflush(stdout);
 
-		ASSERT_EQ(err, -1, "mismatch_rc");
-		ASSERT_HAS_SUBSTR(env.subtest_state->log_buf, "-line one",
-				  "diff_has_expected");
-		ASSERT_HAS_SUBSTR(env.subtest_state->log_buf, "+line two",
-				  "diff_has_actual");
+			ASSERT_EQ(err, -1, "mismatch_rc");
+			ASSERT_HAS_SUBSTR(env.subtest_state->log_buf, "-line one",
+					  "diff_has_expected");
+			ASSERT_HAS_SUBSTR(env.subtest_state->log_buf, "+line two",
+					  "diff_has_actual");
+		}
 		test__end_subtest();
 	}
 }
-- 
2.43.0