ftrace: disable tracing of functions not available in the target kernel

In general we could be interested to defined a common configuration to use
across different kernels. Thus, for a given set of experiments, some
functions can be present only on some kernels and not others.

This patch updates the check for the availability of functions to profile by
ensuring that we consider only functions available in the kernel in use
in the target. In case of a function cannot be profiled in the target kernel
we log a warning instead of raising an exception.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>

devlib/trace/ftrace.py

@@ -59,6 +59,7 @@ class FtraceCollector(TraceCollector):
                  autoreport=True,
                  autoview=False,
                  no_install=False,
+                 strict=False,
                  ):
         super(FtraceCollector, self).__init__(target)
         self.events = events if events is not None else DEFAULT_EVENTS
@@ -75,7 +76,7 @@ class FtraceCollector(TraceCollector):
         self.start_time = None
         self.stop_time = None
         self.event_string = _build_trace_events(self.events)
-        self.function_string = _build_trace_functions(self.functions)
+        self.function_string = None
         self._reset_needed = True
 
         # Setup tracing paths
@@ -111,9 +112,16 @@ class FtraceCollector(TraceCollector):
             # Validate required functions to be traced
             available_functions = self.target.execute(
                     'cat {}'.format(self.available_functions_file)).splitlines()
+            selected_functions = []
             for function in self.functions:
                 if function not in available_functions:
-                    raise TargetError('Function [{}] not available for filtering'.format(function))
+                    message = 'Function [{}] not available for profiling'.format(function)
+                    if strict:
+                        raise TargetError(message)
+                    self.target.logger.warning(message)
+                else:
+                    selected_functions.append(function)
+            self.function_string = _build_trace_functions(selected_functions)
 
     def reset(self):
         if self.buffer_size: