[RFC] ARC: initial ftrace support

[Eugeniy Paltsev]

Add initial ftrace support for ARCv2. We add support only for
function tracer (the simplest, not dynamic one), however it is
prerequisite for dynamic function tracer and other complex
ones.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
---
 arch/arc/Kconfig              |  1 +
 arch/arc/include/asm/Kbuild   |  1 -
 arch/arc/include/asm/ftrace.h | 16 ++++++++++++++++
 arch/arc/kernel/Makefile      | 10 ++++++++++
 arch/arc/kernel/ftrace.c      | 27 +++++++++++++++++++++++++++
 5 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 arch/arc/include/asm/ftrace.h
 create mode 100644 arch/arc/kernel/ftrace.c

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index ff2a393b635c..4b8f750bd32b 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -48,6 +48,7 @@ config ARC
 	select PCI_SYSCALL if PCI
 	select PERF_USE_VMALLOC if ARC_CACHE_VIPT_ALIASING
 	select HAVE_ARCH_JUMP_LABEL if ISA_ARCV2 && !CPU_ENDIAN_BE32
+	select HAVE_FUNCTION_TRACER if ISA_ARCV2
 
 config ARCH_HAS_CACHE_LINE_SIZE
 	def_bool y
diff --git a/arch/arc/include/asm/Kbuild b/arch/arc/include/asm/Kbuild
index 1b505694691e..4e2f55bdf2ff 100644
--- a/arch/arc/include/asm/Kbuild
+++ b/arch/arc/include/asm/Kbuild
@@ -6,7 +6,6 @@ generic-y += div64.h
 generic-y += dma-mapping.h
 generic-y += emergency-restart.h
 generic-y += extable.h
-generic-y += ftrace.h
 generic-y += hardirq.h
 generic-y += hw_irq.h
 generic-y += irq_regs.h
diff --git a/arch/arc/include/asm/ftrace.h b/arch/arc/include/asm/ftrace.h
new file mode 100644
index 000000000000..92303e506edf
--- /dev/null
+++ b/arch/arc/include/asm/ftrace.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 Synopsys, Inc. (www.synopsys.com)
+ *
+ * Author: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
+ */
+
+#ifndef __ASM_ARC_FTRACE_H
+#define __ASM_ARC_FTRACE_H
+
+extern void _mcount(unsigned long parent_ip);
+
+/* 3 instructions 1x 16 bit + 1x 32 bit */
+#define MCOUNT_INSN_SIZE	6
+
+#endif /* __ASM_ARC_FTRACE_H */
diff --git a/arch/arc/kernel/Makefile b/arch/arc/kernel/Makefile
index 75539670431a..42c9c4b1cabd 100644
--- a/arch/arc/kernel/Makefile
+++ b/arch/arc/kernel/Makefile
@@ -22,12 +22,22 @@ obj-$(CONFIG_ARC_METAWARE_HLINK)	+= arc_hostlink.o
 obj-$(CONFIG_PERF_EVENTS)		+= perf_event.o
 obj-$(CONFIG_JUMP_LABEL)		+= jump_label.o
 
+
+obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace.o
+
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
+endif
+
 obj-$(CONFIG_ARC_FPU_SAVE_RESTORE)	+= fpu.o
 ifdef CONFIG_ISA_ARCOMPACT
 CFLAGS_fpu.o   += -mdpfp
 endif
 
 ifdef CONFIG_ARC_DW2_UNWIND
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_ctx_sw.o = $(CC_FLAGS_FTRACE)
+endif
 CFLAGS_ctx_sw.o += -fno-omit-frame-pointer
 obj-y += ctx_sw.o
 else
diff --git a/arch/arc/kernel/ftrace.c b/arch/arc/kernel/ftrace.c
new file mode 100644
index 000000000000..a61edf52bfe2
--- /dev/null
+++ b/arch/arc/kernel/ftrace.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Synopsys, Inc. (www.synopsys.com)
+ *
+ * Author: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
+ */
+
+#include <linux/ftrace.h>
+
+noinline void ftrace_stub(unsigned long ip, unsigned long parent_ip,
+			  struct ftrace_ops *op, struct pt_regs *regs)
+{
+	/* do notning */
+}
+
+extern void (*ftrace_trace_function)(unsigned long, unsigned long,
+				     struct ftrace_ops*, struct pt_regs*);
+
+noinline void _mcount(unsigned long parent_ip)
+{
+	unsigned long ip = (unsigned long)__builtin_return_address(0);
+
+	if (unlikely(ftrace_trace_function != ftrace_stub))
+		ftrace_trace_function(ip - MCOUNT_INSN_SIZE, parent_ip,
+				      NULL, NULL);
+}
+EXPORT_SYMBOL(_mcount);
-- 
2.21.1