ARCv3: Implemented ftrace

arch/arc/Kconfig

@@ -38,6 +38,8 @@ config ARC
 	select HAVE_KERNEL_LZMA
 	select HAVE_KPROBES
 	select HAVE_KRETPROBES
+	select HAVE_FUNCTION_TRACER if ISA_ARCV3
+	select HAVE_FUNCTION_GRAPH_TRACER if ISA_ARCV3
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_PERF_EVENTS
 	select HANDLE_DOMAIN_IRQ

arch/arc/Makefile

@@ -61,6 +61,10 @@ cflags-$(CONFIG_64BIT)		+= 	-mcmodel=large
 cflags-$(CONFIG_ARC_HAS_LL128)	+= 	-m128
 endif
 
+ifdef CONFIG_FTRACE
+cflags-y	+= -fno-omit-frame-pointer
+endif
+
 cflags-y	+= -Wa,-I$(srctree)/arch/arc/include
 
 ifdef CONFIG_ARC_CURR_IN_REG

arch/arc/kernel/Makefile

@@ -13,6 +13,23 @@ else
 obj-y	+= intc-arcv2.o
 endif
 
+ifdef CONFIG_FTRACE
+
+# Currently ftrace only works on arcv3 due to ABI
+ifdef CONFIG_ISA_ARCV3
+
+# ftrace cant be traced (infinite loop)
+CFLAGS_REMOVE_ftrace.o = -pg
+CFLAGS_REMOVE_mcount.o = -pg
+
+
+obj-$(CONFIG_FUNCTION_TRACER)  += mcount.o
+obj-$(CONFIG_FUNCTION_GRAPH_TRACER)    += ftrace.o
+
+endif
+
+endif
+
 obj-$(CONFIG_ISA_ARCOMPACT)		+= entry-compact.o
 obj-$(CONFIG_ISA_ARCV2)			+= entry-arcv2.o
 obj-$(CONFIG_ISA_ARCV3)			+= entry-arcv3.o

arch/arc/kernel/ftrace.c

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Function tracing support for ARC
+ *
+ * Copyright (C) 2023 Synopsys, Inc. (www.synopsys.com)
+ */
+
+#include <linux/ftrace.h>
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+/*
+ * Setup return hook in traced routine
+ * Function copied from riscv
+ */
+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;
+
+	if (unlikely(atomic_read(&current->tracing_graph_pause)))
+		return;
+
+	old = *parent;
+
+	if (!function_graph_enter(old, self_addr, frame_pointer, parent))
+		*parent = return_hooker;
+}
+
+#endif	/* CONFIG_FUNCTION_GRAPH_TRACER */

arch/arc/kernel/mcount.S

@@ -0,0 +1,119 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Function tracing support for ARC
+ *
+ * Copyright (C) 2023 Synopsys, Inc. (www.synopsys.com)
+ */
+
+
+#include <linux/init.h>
+#include <linux/linkage.h>
+#include <asm-generic/export.h>
+#include <asm/asm-macro-64-bit.h>
+
+.text
+; ftrace placeholder, just return to caller
+ENTRY(ftrace_stub)
+    j_s     [blink]
+ENDPROC(ftrace_stub)
+
+; save ABI necessary registers
+.macro SAVE_ABI
+    PUSHR  blink
+    PUSHR  fp
+.endm
+
+.macro LOAD_ABI
+    POPR fp
+    POPR blink
+.endm
+
+.macro SAVE_ABI_RET
+    PUSHR  r0
+    PUSHR  r1
+    PUSHR  blink
+.endm
+
+.macro LOAD_ABI_RET
+    POPR blink
+    POPR r1
+    POPR r0
+.endm
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+; Return to the actual caller
+ENTRY(return_to_handler)
+    ; Save return value (if any) from handled routine
+    SAVE_ABI_RET
+
+    ; Will return true blink on r0
+    MOVA  r0, @ftrace_return_to_handler
+    jl    [r0]
+
+    MOVR r2, r0
+
+    LOAD_ABI_RET
+
+    j [r2]
+
+ENDPROC(return_to_handler)
+#endif
+
+; r0 has the frompc (targets parent ip)
+; blink has the selfpc (target ip)
+ENTRY(_mcount)
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+
+    ; *ftrace_graph_return != ftrace_stub
+    MOVA  r3, ftrace_graph_return
+    LD64  r3, r3
+    MOVA  r4, @ftrace_stub
+    brne  r3, r4, @do_ftrace_graph_caller
+
+    ; *ftrace_graph_entry != *ftrace_graph_entry_stub
+    MOVA  r3, @ftrace_graph_entry
+    LD64  r3, r3
+    MOVA  r4, @ftrace_graph_entry_stub
+    brne  r3, r4, @do_ftrace_graph_caller
+
+#endif
+
+    ; *ftrace_trace_function != ftrace_stub
+    MOVA r2, ftrace_trace_function
+    LD64 r2, r2
+
+    MOVA r3, @ftrace_stub
+    brne r2, r3, @do_trace
+
+    ; Return
+    j_s  [blink]
+
+ENDPROC(_mcount)
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+do_ftrace_graph_caller:
+
+SAVE_ABI
+
+    ADDR r0, fp, 8
+    MOVR  r1, blink
+
+    MOVA  r2, @prepare_ftrace_return
+    jl    [r2]
+
+LOAD_ABI
+
+    j_s  [blink]
+#endif
+
+do_trace:
+SAVE_ABI
+    MOVR r1, r0
+    MOVR r0, blink
+
+    jl   [r2]
+
+LOAD_ABI
+    j_s   [blink]