[PATCH v3 3/3] arm64/ftrace: Make function graph use ftrace directly

[Chengming Zhou <zhouchengming@bytedance.com>]

As we do in commit 0c0593b45c9b ("x86/ftrace: Make function graph
use ftrace directly"), we don't need special hook for graph tracer,
but instead we use graph_ops:func function to install return_hooker.

Since commit 3b23e4991fb6 ("arm64: implement ftrace with regs") add
implementation for FTRACE_WITH_REGS on arm64, we can easily adopt
the same cleanup on arm64. And this cleanup only changes the
FTRACE_WITH_REGS implementation, so the mcount-based implementation
is unaffected.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
Changes in v3:
 - Add comments in ftrace_graph_func() as suggested by Steve.

Changes in v2:
 - Remove FTRACE_WITH_REGS ftrace_graph_caller asm as suggested by Mark.
---
 arch/arm64/include/asm/ftrace.h  |  7 +++++++
 arch/arm64/kernel/entry-ftrace.S | 17 -----------------
 arch/arm64/kernel/ftrace.c       | 17 +++++++++++++++++
 3 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index 1494cfa8639b..dbc45a4157fa 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -80,8 +80,15 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 struct dyn_ftrace;
+struct ftrace_ops;
+struct ftrace_regs;
+
 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
 #define ftrace_init_nop ftrace_init_nop
+
+void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
+		       struct ftrace_ops *op, struct ftrace_regs *fregs);
+#define ftrace_graph_func ftrace_graph_func
 #endif
 
 #define ftrace_return_address(n) return_address(n)
diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index e535480a4069..d42a205ef625 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -97,12 +97,6 @@ SYM_CODE_START(ftrace_common)
 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
 	bl	ftrace_stub
 
-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
-SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
-	nop				// If enabled, this will be replaced
-					// "b ftrace_graph_caller"
-#endif
-
 /*
  * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
  * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
@@ -127,17 +121,6 @@ ftrace_common_return:
 	ret	x9
 SYM_CODE_END(ftrace_common)
 
-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
-SYM_CODE_START(ftrace_graph_caller)
-	ldr	x0, [sp, #S_PC]
-	sub	x0, x0, #AARCH64_INSN_SIZE	// ip (callsite's BL insn)
-	add	x1, sp, #S_LR			// parent_ip (callsite's LR)
-	ldr	x2, [sp, #PT_REGS_SIZE]	   	// parent fp (callsite's FP)
-	bl	prepare_ftrace_return
-	b	ftrace_common_return
-SYM_CODE_END(ftrace_graph_caller)
-#endif
-
 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 
 /*
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 4506c4a90ac1..35eb7c9b5e53 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -268,6 +268,22 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
 }
 
 #ifdef CONFIG_DYNAMIC_FTRACE
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
+		       struct ftrace_ops *op, struct ftrace_regs *fregs)
+{
+	/*
+	 * Athough graph_ops doesn't have FTRACE_OPS_FL_SAVE_REGS set in flags,
+	 * regs can't be NULL in DYNAMIC_FTRACE_WITH_REGS. By design, it should
+	 * be fixed when DYNAMIC_FTRACE_WITH_ARGS is implemented.
+	 */
+	struct pt_regs *regs = arch_ftrace_get_regs(fregs);
+	unsigned long *parent = (unsigned long *)&procedure_link_pointer(regs);
+
+	prepare_ftrace_return(ip, parent, frame_pointer(regs));
+}
+#else
 /*
  * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
  * depending on @enable.
@@ -297,5 +313,6 @@ int ftrace_disable_ftrace_graph_caller(void)
 {
 	return ftrace_modify_graph_caller(false);
 }
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 #endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
-- 
2.20.1