tracing: add a tracer to catch execution time of kernel functions

Impact: add new tracing plugin which can trace full (entry+exit) function calls

This tracer uses the low level function return ftrace plugin to
measure the execution time of the kernel functions.

The first field is the caller of the function, the second is the
measured function, and the last one is the execution time in
nanoseconds.

- v3:

- HAVE_FUNCTION_RET_TRACER have been added. Each arch that support ftrace return
  should enable it.
- ftrace_return_stub becomes ftrace_stub.
- CONFIG_FUNCTION_RET_TRACER depends now on CONFIG_FUNCTION_TRACER
- Return traces printing can be used for other tracers on trace.c
- Adapt to the new tracing API (no more ctrl_update callback)
- Correct the check of "disabled" during insertion.
- Minor changes...

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/Kconfig

@@ -9,6 +9,9 @@ config NOP_TRACER
 config HAVE_FUNCTION_TRACER
 	bool
 
+config HAVE_FUNCTION_RET_TRACER
+	bool
+
 config HAVE_FUNCTION_TRACE_MCOUNT_TEST
 	bool
 	help
@@ -54,6 +57,17 @@ config FUNCTION_TRACER
 	  (the bootup default), then the overhead of the instructions is very
 	  small and not measurable even in micro-benchmarks.
 
+config FUNCTION_RET_TRACER
+	bool "Kernel Function return Tracer"
+	depends on !DYNAMIC_FTRACE
+	depends on HAVE_FUNCTION_RET_TRACER
+	depends on FUNCTION_TRACER
+	help
+	  Enable the kernel to trace a function at its return.
+	  It's first purpose is to trace the duration of functions.
+	  This is done by setting the current return address on the thread
+	  info structure of the current task.
+
 config IRQSOFF_TRACER
 	bool "Interrupts-off Latency Tracer"
 	default n