csky: basic ftrace supported

When gcc with -pg, it'll add _mcount stub in every function. We need
implement the _mcount in kernel and ftrace depends on stackstrace.

To do: call-graph, dynamic ftrace
Signed-off-by: Guo Ren <ren_guo@c-sky.com>

arch/csky/Kconfig

@@ -29,6 +29,7 @@ config CSKY
 	select GENERIC_SCHED_CLOCK
 	select GENERIC_SMP_IDLE_THREAD
 	select HAVE_ARCH_TRACEHOOK
+	select HAVE_FUNCTION_TRACER
 	select HAVE_GENERIC_DMA_COHERENT
 	select HAVE_KERNEL_GZIP
 	select HAVE_KERNEL_LZO

arch/csky/abiv2/Makefile

@@ -8,3 +8,4 @@ obj-y				+= strcmp.o
 obj-y				+= strcpy.o
 obj-y				+= strlen.o
 obj-y				+= strksyms.o
+obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o

arch/csky/abiv2/mcount.S

+/* SPDX-License-Identifier: GPL-2.0 */
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#include <linux/linkage.h>
+
+ENTRY (_mcount)
+	subi	sp, 20
+	stw	a0, (sp, 0)
+	stw	a1, (sp, 4)
+	stw	a2, (sp, 8)
+	stw	a3, (sp, 12)
+	stw	lr, (sp, 16)
+	mov	a1, lr
+	ldw	a0, (sp, 20)
+	jsri    csky_mcount
+	ldw	a0, (sp, 0)
+	ldw	a1, (sp, 4)
+	ldw	a2, (sp, 8)
+	ldw	a3, (sp, 12)
+	ldw	t1, (sp, 16)
+	ldw	lr, (sp, 20)
+	addi	sp, 24
+	jmp	t1
+END (_mcount)

arch/csky/include/asm/ftrace.h

+/* SPDX-License-Identifier: GPL-2.0 */
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#ifndef __ASM_CSKY_FTRACE_H
+#define __ASM_CSKY_FTRACE_H
+
+extern void _mcount(unsigned long from_pc);
+
+#endif /* __ASM_CSKY_FTRACE_H */

arch/csky/kernel/Makefile

@@ -6,4 +6,9 @@ obj-y += process.o cpu-probe.o ptrace.o dumpstack.o
 
 obj-$(CONFIG_MODULES)			+= module.o
 obj-$(CONFIG_SMP)			+= smp.o
+obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace.o
 obj-$(CONFIG_STACKTRACE)		+= stacktrace.o
+
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
+endif

arch/csky/kernel/ftrace.c

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#include <linux/ftrace.h>
+#include <linux/uaccess.h>
+
+extern void (*ftrace_trace_function)(unsigned long, unsigned long,
+				     struct ftrace_ops*, struct pt_regs*);
+
+
+noinline void __naked ftrace_stub(unsigned long ip, unsigned long parent_ip,
+				  struct ftrace_ops *op, struct pt_regs *regs)
+{
+	asm volatile ("\n");
+}
+
+noinline void csky_mcount(unsigned long from_pc, unsigned long self_pc)
+{
+	if (ftrace_trace_function != ftrace_stub)
+		ftrace_trace_function(self_pc, from_pc, NULL, NULL);
+}
+
+/* _mcount is defined in abi's mcount.S */
+EXPORT_SYMBOL(_mcount);