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 ARM platform.

We introduce a new structure called fgraph_ret_regs for the ARM 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>
---
v10:
 - Use CONFIG_FUNCTION_GRAPH_TRACER to control fgraph_ret_regs definition

v9:
 - Fix stack pointer align issues
 - Update the commit message

v8:
 - Modify the control range of CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
---
 arch/arm/Kconfig               |  1 +
 arch/arm/include/asm/ftrace.h  | 22 ++++++++++++++++++++++
 arch/arm/kernel/asm-offsets.c  |  8 +++++++-
 arch/arm/kernel/entry-ftrace.S | 10 ++++++----
 4 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index e24a9820e12f..73061379855a 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig

@@ -98,6 +98,7 @@ config ARM
 	select HAVE_FAST_GUP if ARM_LPAE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_ERROR_INJECTION
+	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
 	select HAVE_GCC_PLUGINS

diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 7e9251ca29fe..3c457902b355 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h

@@ -77,4 +77,26 @@ static inline bool arch_syscall_match_sym_name(const char *sym,
 
 #endif /* ifndef __ASSEMBLY__ */
 
+#ifndef __ASSEMBLY__
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+struct fgraph_ret_regs {
+	/* r0 - r3 */
+	unsigned long regs[4];
+
+	unsigned long fp;
+	unsigned long __unused;
+};
+
+static inline unsigned long fgraph_ret_regs_return_value(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->regs[0];
+}
+
+static inline unsigned long fgraph_ret_regs_frame_pointer(struct fgraph_ret_regs *ret_regs)
+{
+	return ret_regs->fp;
+}
+#endif /* ifdef CONFIG_FUNCTION_GRAPH_TRACER */
+#endif
+
 #endif /* _ASM_ARM_FTRACE */

diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 38121c59cbc2..18bb85115b21 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c

@@ -23,6 +23,7 @@
 #include <asm/suspend.h>
 #include <asm/vdso_datapage.h>
 #include <asm/hardware/cache-l2x0.h>
+#include <asm/ftrace.h>
 #include <linux/kbuild.h>
 #include <linux/arm-smccc.h>
 #include "signal.h"

@@ -170,5 +171,10 @@ int main(void)
   DEFINE(KEXEC_INDIR_PAGE,	offsetof(struct kexec_relocate_data, kexec_indirection_page));
   DEFINE(KEXEC_MACH_TYPE,	offsetof(struct kexec_relocate_data, kexec_mach_type));
   DEFINE(KEXEC_R2,		offsetof(struct kexec_relocate_data, kexec_r2));
-  return 0; 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+  BLANK();
+  DEFINE(FGRET_REGS_SIZE,	sizeof(struct fgraph_ret_regs));
+  BLANK();
+#endif
+  return 0;
 }

diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index 3e7bcaca5e07..d41a1676608c 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S

@@ -257,11 +257,13 @@ ENDPROC(ftrace_graph_regs_caller)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 ENTRY(return_to_handler)
-	stmdb	sp!, {r0-r3}
-	add	r0, sp, #16		@ sp at exit of instrumented routine
+	mov	ip, sp				@ sp at exit of instrumented routine
+	stmdb	sp!, {r0-r3, ip, lr}		@ fill fgraph_ret_regs
+	mov	r0, sp
 	bl	ftrace_return_to_handler
-	mov	lr, r0			@ r0 has real ret addr
-	ldmia	sp!, {r0-r3}
+	mov	lr, r0				@ r0 has real ret addr
+	ldmia	sp, {r0-r3}
+	add	sp, sp, #FGRET_REGS_SIZE	@ restore stack pointer
 	ret	lr
 ENDPROC(return_to_handler)
 #endif