ARCv2: Support ftrace and function graph tracer

Added support for both FTRACE and FUNCTION_GRAPH_TRACER (GCC > 14) in ARCv2

Signed-off-by: Bruno Mauricio <brunoasmauricio@gmail.com>

Author: BrunoASMauricio

arch/arc/Kconfig

@@ -32,6 +32,8 @@ config ARC
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if ARC_MMU_V4
 	select HAVE_DEBUG_STACKOVERFLOW
 	select HAVE_DEBUG_KMEMLEAK
+	select HAVE_FUNCTION_TRACER if ISA_ARCV2
+	select HAVE_FUNCTION_GRAPH_TRACER if (ISA_ARCV2 && GCC_VERSION >= 140000)
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select HAVE_IOREMAP_PROT if !(ISA_ARCV3 && !64BIT)
 	select HAVE_KERNEL_GZIP

arch/arc/kernel/Makefile

@@ -7,6 +7,16 @@ obj-y	:= arcksyms.o setup.o irq.o reset.o ptrace.o process.o devtree.o
 obj-y	+= signal.o traps.o sys.o troubleshoot.o stacktrace.o disasm.o
 obj-y	+= ctx_sw_asm.o
 
+ifdef CONFIG_FTRACE
+# ftrace can't 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
+
 ifdef CONFIG_ISA_ARCOMPACT
 obj-y	+= intc-compact.o
 else

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 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Function tracing support for ARC
+ *
+ * Copyright (C) 2023 Synopsys, Inc. (www.synopsys.com)
+ */
+
+#include <linux/linkage.h>
+#include <asm-generic/export.h>
+
+; ftrace placeholder, just return to caller
+ENTRY(ftrace_stub)
+	j_s	[blink]
+ENDPROC(ftrace_stub)
+
+.macro SAVE_ABI
+	push	blink
+.endm
+
+.macro LOAD_ABI
+	pop	blink
+.endm
+
+.macro SAVE_ABI_RET
+	push	r0
+	push	r1
+.endm
+
+.macro LOAD_ABI_RET
+	pop	r1
+	pop	r0
+.endm
+
+; 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
+	ld	r3, [ftrace_graph_return]
+	brne	r3, @ftrace_stub, @do_ftrace_graph_caller
+	; *ftrace_graph_entry != *ftrace_graph_entry_stub
+	ld	r3, [ftrace_graph_entry]
+	brne	r3, @ftrace_graph_entry_stub, @do_ftrace_graph_caller
+
+#endif
+
+	; *ftrace_trace_function != ftrace_stub
+	ld	r2, [ftrace_trace_function]
+	brne	r2, @ftrace_stub, @do_trace
+	; Return
+	j_s	[blink]
+
+ENDPROC(_mcount)
+
+#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
+	jl	ftrace_return_to_handler
+	mov	r2, r0
+	LOAD_ABI_RET
+	j	[r2]
+
+ENDPROC(return_to_handler)
+
+do_ftrace_graph_caller:
+	; ABI does not allow us to infer blink location
+	; ARC GCC port inserts into r1 the delta between the pushed blink and
+	; the sp at call time
+	; We perform calculation before any push (sp change) happens
+	add	r0, r1, sp
+	SAVE_ABI
+	sub	r0, r0, 4
+	mov	r1, blink
+	jl	prepare_ftrace_return
+	LOAD_ABI
+	j_s	[blink]
+#endif
+
+do_trace:
+	SAVE_ABI
+	mov	r1, r0
+	mov	r0, blink
+	jl	[r2]
+	; load ABI state and jump to blink (in stack)
+	LOAD_ABI
+	j_s	[blink]
+
+EXPORT_SYMBOL(_mcount)