[PATCH bpf-next v3 4/4] selftests/bpf: Test verifier warning logging

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Add coverage for explicit verifier warning logging and for libbpf's
default warning flush path while keeping the warning bit private to the
test.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../bpf/prog_tests/kfunc_implicit_args.c      | 92 +++++++++++++++++++
 1 file changed, 92 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_implicit_args.c b/tools/testing/selftests/bpf/prog_tests/kfunc_implicit_args.c
index 5e4793c9c29a..f92a27d76455 100644
--- a/tools/testing/selftests/bpf/prog_tests/kfunc_implicit_args.c
+++ b/tools/testing/selftests/bpf/prog_tests/kfunc_implicit_args.c
@@ -4,7 +4,99 @@
 #include <test_progs.h>
 #include "kfunc_implicit_args.skel.h"
 
+#define TEST_BPF_LOG_LEVEL_WARN	(1U << 4)
+
+static size_t libbpf_log_pos;
+static char libbpf_log_buf[4096];
+static bool libbpf_log_error;
+
+static int libbpf_print_cb(enum libbpf_print_level level, const char *fmt, va_list args)
+{
+	int emitted_cnt;
+	size_t left_cnt;
+
+	(void)level;
+
+	left_cnt = sizeof(libbpf_log_buf) - libbpf_log_pos;
+	emitted_cnt = vsnprintf(libbpf_log_buf + libbpf_log_pos, left_cnt, fmt, args);
+	if (emitted_cnt < 0 || emitted_cnt + 1 > left_cnt) {
+		libbpf_log_error = true;
+		return 0;
+	}
+
+	libbpf_log_pos += emitted_cnt;
+	return 0;
+}
+
+static void select_legacy_impl_prog(struct kfunc_implicit_args *skel)
+{
+	struct bpf_program *prog;
+
+	bpf_object__for_each_program(prog, skel->obj)
+		bpf_program__set_autoload(prog,
+					  prog == skel->progs.test_kfunc_implicit_arg_legacy_impl);
+}
+
+static void test_warn_bit(void)
+{
+	struct kfunc_implicit_args *skel;
+	char log_buf[4096] = {};
+	int err;
+
+	skel = kfunc_implicit_args__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	select_legacy_impl_prog(skel);
+	bpf_program__set_log_buf(skel->progs.test_kfunc_implicit_arg_legacy_impl,
+				 log_buf, sizeof(log_buf));
+	bpf_program__set_log_level(skel->progs.test_kfunc_implicit_arg_legacy_impl,
+				   TEST_BPF_LOG_LEVEL_WARN);
+
+	err = kfunc_implicit_args__load(skel);
+	ASSERT_OK(err, "skel_load");
+	ASSERT_OK_PTR(strstr(log_buf, "uses deprecated kfunc bpf_kfunc_implicit_arg_legacy_impl()"),
+		      "warning_msg");
+	ASSERT_NULL(strstr(log_buf, "processed "), "no_verbose_log");
+
+	kfunc_implicit_args__destroy(skel);
+}
+
+static void test_default_warning_flush(void)
+{
+	libbpf_print_fn_t old_print_cb = libbpf_set_print(libbpf_print_cb);
+	struct kfunc_implicit_args *skel = NULL;
+	int err;
+
+	libbpf_log_pos = 0;
+	libbpf_log_buf[0] = '\0';
+	libbpf_log_error = false;
+
+	skel = kfunc_implicit_args__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		goto cleanup;
+
+	select_legacy_impl_prog(skel);
+
+	err = kfunc_implicit_args__load(skel);
+	ASSERT_OK(err, "skel_load");
+	ASSERT_FALSE(libbpf_log_error, "libbpf_log_error");
+	ASSERT_OK_PTR(strstr(libbpf_log_buf, "-- BEGIN PROG LOAD WARNINGS --"), "warn_banner");
+	ASSERT_OK_PTR(strstr(libbpf_log_buf,
+			     "uses deprecated kfunc bpf_kfunc_implicit_arg_legacy_impl()"),
+		      "warn_msg");
+	ASSERT_NULL(strstr(libbpf_log_buf, "-- BEGIN PROG LOAD LOG --"), "no_verbose_log");
+
+cleanup:
+	kfunc_implicit_args__destroy(skel);
+	libbpf_set_print(old_print_cb);
+}
+
 void test_kfunc_implicit_args(void)
 {
 	RUN_TESTS(kfunc_implicit_args);
+	if (test__start_subtest("warn_bit"))
+		test_warn_bit();
+	if (test__start_subtest("default_warning_flush"))
+		test_default_warning_flush();
 }
-- 
2.52.0