[PATCH] ARM: ftrace: Allow function graph tracer to have its own trampoline

[Steven Rostedt (Red Hat)]

The ftrace infrastructure now allows the function graph tracer
trampoline to be called directly instead of having to first go
through the function tracer trampoline. But in order for this to
work, the function graph tracer must be dependent from the function
tracer trampoline. Currently in ARM, the function graph tracer
does not save registers as it depends on the function tracer
trampoline to do so.

By adding a ftrace_graph_tramp_caller function that saves the regs
then does the function graph tracing work, this can be used as
the trampoline for function graph tracing.

Link: http://lkml.kernel.org/r/53BED155.9040607@xxxxxxxxxx

Reported-by: Tuomas Tynkkynen <ttynkkynen@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 arch/arm/include/asm/ftrace.h  | 5 +++++
 arch/arm/kernel/entry-common.S | 7 +++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 39eb16b..6af3929 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -54,6 +54,11 @@ extern inline void *return_address(unsigned int level)
 
 #define ftrace_return_address(n) return_address(n)
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+extern void ftrace_graph_tramp_caller(void);
+#define FTRACE_GRAPH_TRAMP_ADDR ((unsigned long)ftrace_graph_tramp_caller)
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 #endif /* ifndef __ASSEMBLY__ */
 
 #endif /* _ASM_ARM_FTRACE */
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 7139d4a..0199167 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -314,6 +314,13 @@ ENDPROC(ftrace_caller)
 #endif
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ENTRY(ftrace_graph_tramp_caller)
+UNWIND(.fnstart)
+	mcount_enter
+	__ftrace_graph_caller
+UNWIND(.fnend)
+ENDPROC(ftrace_graph_tramp_caller)
+
 ENTRY(ftrace_graph_caller)
 UNWIND(.fnstart)
 	__ftrace_graph_caller
-- 
1.8.1.4


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