Subject: [PATCH bpf-next v4 04/27] tracing: Add trampoline/graph selftest

From: Jiri Olsa <[email-masked]>
Date: Thu, 26 Aug 2021 21:38:59 +0200

Adding selftest for checking that direct trampoline can
co-exist together with graph tracer on same function.

This is supported for CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
config option, which is defined only for x86_64 for now.

Signed-off-by: Jiri Olsa <[email-masked]>
---
 kernel/trace/trace_selftest.c | 49 ++++++++++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index adf7ef194005..f8e55b949cdd 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -750,6 +750,8 @@ static struct fgraph_ops fgraph_ops __initdata  = {
 	.retfunc		= &trace_graph_return,
 };
 
+noinline __noclone static void trace_direct_tramp(void) { }
+
 /*
  * Pretty much the same than for the function tracer from which the selftest
  * has been borrowed.
@@ -760,6 +762,7 @@ trace_selftest_startup_function_graph(struct tracer *trace,
 {
 	int ret;
 	unsigned long count;
+	char *func_name __maybe_unused;
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 	if (ftrace_filter_param) {
@@ -808,8 +811,52 @@ trace_selftest_startup_function_graph(struct tracer *trace,
 		goto out;
 	}
 
-	/* Don't test dynamic tracing, the function tracer already did */
+#ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+	tracing_reset_online_cpus(&tr->array_buffer);
+	set_graph_array(tr);
 
+	/*
+	 * Some archs *cough*PowerPC*cough* add characters to the
+	 * start of the function names. We simply put a '*' to
+	 * accommodate them.
+	 */
+	func_name = "*" __stringify(DYN_FTRACE_TEST_NAME);
+	ftrace_set_global_filter(func_name, strlen(func_name), 1);
+
+	/*
+	 * Register direct function together with graph tracer
+	 * and make sure we get graph trace.
+	 */
+	ret = register_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
+				     (unsigned long) trace_direct_tramp);
+	if (ret)
+		goto out;
+
+	ret = register_ftrace_graph(&fgraph_ops);
+	if (ret) {
+		warn_failed_init_tracer(trace, ret);
+		goto out;
+	}
+
+	DYN_FTRACE_TEST_NAME();
+
+	count = 0;
+
+	tracing_stop();
+	/* check the trace buffer */
+	ret = trace_test_buffer(&tr->array_buffer, &count);
+
+	unregister_ftrace_graph(&fgraph_ops);
+
+	tracing_start();
+
+	if (!ret && !count) {
+		ret = -1;
+		goto out;
+	}
+#endif
+
+	/* Don't test dynamic tracing, the function tracer already did */
 out:
 	/* Stop it if we failed */
 	if (ret)
-- 
2.31.1