[PATCH v7 3/8] ARM: ftrace: Enable HAVE_FUNCTION_GRAPH_RETVAL

[Donglin Peng]

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
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 <pengdonglin@xxxxxxxxxxxxxx>
---
 arch/arm/Kconfig               |  1 +
 arch/arm/include/asm/ftrace.h  | 22 ++++++++++++++++++++++
 arch/arm/kernel/entry-ftrace.S |  6 +++++-
 3 files changed, 28 insertions(+), 1 deletion(-)

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..e3bed4949558 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_HAVE_FUNCTION_GRAPH_RETVAL
+struct fgraph_ret_regs {
+	unsigned long regs[4];
+	unsigned long fp;
+};
+
+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
+
+#endif
+
 #endif /* _ASM_ARM_FTRACE */
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index 3e7bcaca5e07..5f1e74555b25 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S
@@ -257,11 +257,15 @@ ENDPROC(ftrace_graph_regs_caller)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 ENTRY(return_to_handler)
+	sub	sp, sp, #4
 	stmdb	sp!, {r0-r3}
-	add	r0, sp, #16		@ sp at exit of instrumented routine
+	add	r0, sp, #20		@ sp at exit of instrumented routine
+	str	r0, [sp, #16]
+	mov	r0, sp
 	bl	ftrace_return_to_handler
 	mov	lr, r0			@ r0 has real ret addr
 	ldmia	sp!, {r0-r3}
+	add	sp, sp, #4		@ skip fp
 	ret	lr
 ENDPROC(return_to_handler)
 #endif
-- 
2.25.1