selftests/bpf: Add selftest for dynamic tracepoint

The result is as follows,

  $ tools/testing/selftests/bpf/test_progs --name=dynamic_tp
  torvalds#85      dynamic_tp:OK
  Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>

tools/testing/selftests/bpf/prog_tests/test_dynamic_tp.c

@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+#include <bpf/bpf.h>
+
+#include "dynamic_tp.skel.h"
+
+int dynamic_tp(const char *cmd)
+{
+	const char *kprobe_file = "/sys/kernel/debug/tracing/kprobe_events";
+	ssize_t bytes_written;
+	int fd, err;
+
+	fd = open(kprobe_file, O_WRONLY | O_APPEND);
+	if (!ASSERT_GE(fd, 0, "open kprobe_events"))
+		return -1;
+
+	bytes_written = write(fd, cmd, strlen(cmd));
+	if (!ASSERT_GT(bytes_written, 0, "write kprobe_events")) {
+		close(fd);
+		return -1;
+	}
+
+	err = close(fd);
+	if (!ASSERT_OK(err, "close kprobe_events"))
+		return -1;
+	return 0;
+}
+
+void test_dynamic_tp(void)
+{
+	struct dynamic_tp *skel;
+	pid_t child_pid;
+	int status, err;
+
+	/* create a dynamic tracepoint */
+	err = dynamic_tp("p:my_dynamic_tp kernel_clone");
+	if (!ASSERT_OK(err, "create dynamic tp"))
+		return;
+
+	skel = dynamic_tp__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "load progs"))
+		goto remove_tp;
+	skel->bss->pid = getpid();
+	err = dynamic_tp__attach(skel);
+	if (!ASSERT_OK(err, "attach progs"))
+		goto cleanup;
+
+	/* trigger the dynamic tracepoint */
+	child_pid = fork();
+	if (!ASSERT_GT(child_pid, -1, "child_pid"))
+		goto cleanup;
+	if (child_pid == 0)
+		_exit(0);
+	waitpid(child_pid, &status, 0);
+
+	ASSERT_EQ(skel->bss->result, 1, "result");
+
+cleanup:
+	dynamic_tp__destroy(skel);
+remove_tp:
+	dynamic_tp("-:my_dynamic_tp kernel_clone");
+}

tools/testing/selftests/bpf/progs/dynamic_tp.c

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+#define MAX_STACK_TRACE_DEPTH 32
+unsigned long entries[MAX_STACK_TRACE_DEPTH] = {};
+#define SIZE_OF_ULONG (sizeof(unsigned long))
+
+int result, pid;
+
+SEC("kprobe/kprobes/my_dynamic_tp")
+int dynamic_tp(struct pt_regs *ctx)
+{
+	int ret;
+
+	ret = bpf_get_stack(ctx, entries, MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, 0);
+	if (ret < 0) {
+		result = -1;
+		return ret;
+	}
+	if (bpf_get_current_pid_tgid() >> 32 == pid)
+		result = 1;
+	return 0;
+}