[for-next][PATCH 13/13] riscv: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

[Steven Rostedt <rostedt@goodmis.org>]

From: Donglin Peng <pengdonglin@sangfor.com.cn>

The previous patch ("function_graph: Support recording and printing
the return value of function") has laid the groundwork for the for
the funcgraph-retval, and this modification makes it available on
the RISC-V platform.

We introduce a new structure called fgraph_ret_regs for the RISC-V
platform to hold return registers and the frame pointer. We then
fill its content in the return_to_handler and pass its address to
the function ftrace_return_to_handler to record the return value.

Link: https://lore.kernel.org/linux-trace-kernel/a8d71b12259f90e7e63d0ea654fcac95b0232bbc.1680954589.git.pengdonglin@sangfor.com.cn

Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ftrace.h | 21 +++++++++++++++++++++
 arch/riscv/kernel/mcount.S      |  7 +------
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 2bb0c38419ff..62c1e375183c 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -146,6 +146,7 @@ config RISCV
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER
+	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
 
 config CLANG_SUPPORTS_DYNAMIC_FTRACE
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index d47d87c2d7e3..740a979171e5 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -111,4 +111,25 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
 
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
+#ifndef __ASSEMBLY__
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+struct fgraph_ret_regs {
+	unsigned long a1;
+	unsigned long a0;
+	unsigned long s0;
+	unsigned long ra;
+};
+
+static inline unsigned long fgraph_ret_regs_return_value(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->a0;
+}
+
+static inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->s0;
+}
+#endif /* ifdef CONFIG_FUNCTION_GRAPH_TRACER */
+#endif
+
 #endif /* _ASM_RISCV_FTRACE_H */
diff --git a/arch/riscv/kernel/mcount.S b/arch/riscv/kernel/mcount.S
index 30102aadc4d7..8a6e5a9e842a 100644
--- a/arch/riscv/kernel/mcount.S
+++ b/arch/riscv/kernel/mcount.S
@@ -65,13 +65,8 @@ ENTRY(return_to_handler)
  * So alternatively we check the *old* frame pointer position, that is, the
  * value stored in -16(s0) on entry, and the s0 on return.
  */
-#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
-	mv	t6, s0
-#endif
 	SAVE_RET_ABI_STATE
-#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
-	mv	a0, t6
-#endif
+	mv	a0, sp
 	call	ftrace_return_to_handler
 	mv	a2, a0
 	RESTORE_RET_ABI_STATE
-- 
2.39.2