Re: [PATCH v8 7/8] LoongArch: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

The commit d4815c5d1bbd ("function_graph: Support recording and
printing the return value of function") laid the groundwork for the
for the funcgraph-retval, and this modification makes it available
on the LoongArch platform.

We introduce a new structure called fgraph_ret_regs for the LoongArch
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.

Signed-off-by: Donglin Peng <redacted>
---
v8:
  - Modify the control range of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
---
  arch/loongarch/Kconfig              |  1 +
  arch/loongarch/include/asm/ftrace.h | 18 ++++++++++++++++++
  arch/loongarch/kernel/mcount.S      |  6 ++++--
  arch/loongarch/kernel/mcount_dyn.S  |  7 ++++---
  4 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 7fd51257e0ed..4bf60132869b 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig

@@ -99,6 +99,7 @@ config LOONGARCH
  	select HAVE_FAST_GUP
  	select HAVE_FTRACE_MCOUNT_RECORD
  	select HAVE_FUNCTION_ARG_ACCESS_API
+	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
  	select HAVE_FUNCTION_GRAPH_TRACER
  	select HAVE_FUNCTION_TRACER
  	select HAVE_GENERIC_VDSO

diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
index 3418d32d4fc7..433c6218888b 100644
--- a/arch/loongarch/include/asm/ftrace.h
+++ b/arch/loongarch/include/asm/ftrace.h

@@ -63,4 +63,22 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
  
  #endif /* CONFIG_FUNCTION_TRACER */
  
+#ifndef __ASSEMBLY__
+struct fgraph_ret_regs {
+	unsigned long a0;
+	unsigned long a1;
+	unsigned long fp;
+};

+
+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->fp;
+}
+#endif
+
  #endif /* _ASM_LOONGARCH_FTRACE_H */

diff --git a/arch/loongarch/kernel/mcount.S b/arch/loongarch/kernel/mcount.S
index 8cdc1563cd33..3e405c0212c0 100644
--- a/arch/loongarch/kernel/mcount.S
+++ b/arch/loongarch/kernel/mcount.S

@@ -79,10 +79,12 @@ SYM_FUNC_START(ftrace_graph_caller)
  SYM_FUNC_END(ftrace_graph_caller)
  
  SYM_FUNC_START(return_to_handler)
-	PTR_ADDI	sp, sp, -2 * SZREG
+	PTR_ADDI	sp, sp, -3 * SZREG

  	PTR_S		a0, sp, 0
  	PTR_S		a1, sp, SZREG
+	PTR_S		zero, sp, 2 * SZREG
  
+	move		a0, sp
  	bl		ftrace_return_to_handler
  
  	/* Restore the real parent address: a0 -> ra */

@@ -90,7 +92,7 @@ SYM_FUNC_START(return_to_handler)
  
  	PTR_L		a0, sp, 0
  	PTR_L		a1, sp, SZREG
-	PTR_ADDI	sp, sp, 2 * SZREG
+	PTR_ADDI	sp, sp, 3 * SZREG
  	jr		ra
  SYM_FUNC_END(return_to_handler)
  #endif /* CONFIG_FUNCTION_GRAPH_TRACER */

diff --git a/arch/loongarch/kernel/mcount_dyn.S b/arch/loongarch/kernel/mcount_dyn.S
index bbabf06244c2..ab85a953c6d3 100644
--- a/arch/loongarch/kernel/mcount_dyn.S
+++ b/arch/loongarch/kernel/mcount_dyn.S

@@ -131,18 +131,19 @@ SYM_CODE_END(ftrace_graph_caller)
  
  SYM_CODE_START(return_to_handler)
  	/* Save return value regs */
-	PTR_ADDI 	sp, sp, -2 * SZREG
+	PTR_ADDI 	sp, sp, -3 * SZREG