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>
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index ab8baf7..196f62f 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -2,6 +2,11 @@
 # Makefile for the RISC-V Linux kernel
 #
 
+ifdef CONFIG_FTRACE
+CFLAGS_REMOVE_ftrace.o = -pg
+CFLAGS_REMOVE_setup.o = -pg
+endif
+
 extra-y += head.o
 extra-y += vmlinux.lds
 
@@ -29,5 +34,7 @@
 obj-$(CONFIG_SMP)		+= smpboot.o
 obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_MODULES)		+= module.o
+obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o
+obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o
 
 clean: