[PATCH 6/6] riscv/ftrace: Add HAVE_FUNCTION_GRAPH_RET_ADDR_PTR support

[Alan Kao]

When doing unwinding in the function walk_stackframe, the pc now receives 
the address from calling ftrace_graph_ret_addr instead of manual calculation.

Note that the original expression,
	pc = frame->ra - 4
is buggy if the instruction at the return address happened to be a
compressed inst. But since it is not a critical part of ftrace and
is a RISC-V-specific behavior, it is ignored for now to ease the 
review process.

Cc: Greentime Hu <greentime@xxxxxxxxxxxxx>
Signed-off-by: Alan Kao <alankao@xxxxxxxxxxxxx>
---
 arch/riscv/include/asm/ftrace.h | 1 +
 arch/riscv/kernel/ftrace.c      | 2 +-
 arch/riscv/kernel/stacktrace.c  | 6 ++++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 429a6a156645..6e4b4c96b63e 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -8,6 +8,7 @@
 #if defined(CONFIG_FUNCTION_GRAPH_TRACER) && defined(CONFIG_FRAME_POINTER)
 #define HAVE_FUNCTION_GRAPH_FP_TEST
 #endif
+#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 
 #define ARCH_SUPPORTS_FTRACE_OPS 1
 #ifndef __ASSEMBLY__
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index c9cc884961d7..e02ecd44fe47 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -144,7 +144,7 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 		return;
 
 	err = ftrace_push_return_trace(old, self_addr, &trace.depth,
-				       frame_pointer, NULL);
+				       frame_pointer, parent);
 	if (err == -EBUSY)
 		return;
 	*parent = return_hooker;
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 559aae781154..a4b1d94371a0 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -18,6 +18,7 @@
 #include <linux/sched/debug.h>
 #include <linux/sched/task_stack.h>
 #include <linux/stacktrace.h>
+#include <linux/ftrace.h>
 
 #ifdef CONFIG_FRAME_POINTER
 
@@ -63,7 +64,12 @@ static void notrace walk_stackframe(struct task_struct *task,
 		frame = (struct stackframe *)fp - 1;
 		sp = fp;
 		fp = frame->fp;
+#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
+		pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
+					   (unsigned long *)(fp - 8));
+#else
 		pc = frame->ra - 0x4;
+#endif
 	}
 }
 
-- 
2.15.1