riscv/ftrace: Add basic support

This patch contains basic ftrace support for RV64I platform.
Specifically, function tracer (HAVE_FUNCTION_TRACER), function graph
tracer (HAVE_FUNCTION_GRAPH_TRACER), and a frame pointer test
(HAVE_FUNCTION_GRAPH_FP_TEST) are implemented following the
instructions in Documentation/trace/ftrace-design.txt.

Note that the functions in both ftrace.c and setup.c should not be
hooked with the compiler's -pg option: to prevent infinite self-
referencing for the former, and to ignore early setup stuff for the
latter.

Signed-off-by: Alan Kao <alankao@andestech.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
new file mode 100644
index 000000000000..d0de68d144cb
--- /dev/null
+++ b/arch/riscv/kernel/ftrace.c
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2013 Linaro Limited
+ * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
+ * Copyright (C) 2017 Andes Technology Corporation
+ */
+
+#include <linux/ftrace.h>
+
+/*
+ * Most of this file is copied from arm64.
+ */
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
+			   unsigned long frame_pointer)
+{
+	unsigned long return_hooker = (unsigned long)&return_to_handler;
+	unsigned long old;
+	struct ftrace_graph_ent trace;
+	int err;
+
+	if (unlikely(atomic_read(&current->tracing_graph_pause)))
+		return;
+
+	/*
+	 * We don't suffer access faults, so no extra fault-recovery assembly
+	 * is needed here.
+	 */
+	old = *parent;
+
+	trace.func = self_addr;
+	trace.depth = current->curr_ret_stack + 1;
+
+	if (!ftrace_graph_entry(&trace))
+		return;
+
+	err = ftrace_push_return_trace(old, self_addr, &trace.depth,
+				       frame_pointer, NULL);
+	if (err == -EBUSY)
+		return;
+	*parent = return_hooker;
+}