Add initial support for LD_PRELOAD in Trace action

tracetools_launch/tracetools_launch/action.py

@@ -14,10 +14,14 @@
 
 """Module for the Trace action."""
 
+import re
+import subprocess
 from typing import List
 from typing import Optional
+from typing import Union
 
 from launch.action import Action
+from launch.actions import SetEnvironmentVariable
 from launch.event import Event
 from launch.event_handlers import OnShutdown
 from launch.launch_context import LaunchContext
@@ -33,6 +37,10 @@ class Trace(Action):
     Sets up and enables tracing through a launch file description.
     """
 
+    PROFILE_LIB_NORMAL = 'liblttng-ust-cyg-profile.so'
+    PROFILE_LIB_FAST = 'liblttng-ust-cyg-profile-fast.so'
+    PROFILE_PATTERN = '^lttng_ust_cyg_profile.*:func_.*'
+
     def __init__(
         self,
         *,
@@ -41,6 +49,7 @@ class Trace(Action):
         base_path: str = path.DEFAULT_BASE_PATH,
         events_ust: List[str] = names.DEFAULT_EVENTS_ROS,
         events_kernel: List[str] = names.DEFAULT_EVENTS_KERNEL,
+        profile_fast: bool = True,
         **kwargs,
     ) -> None:
         """
@@ -51,6 +60,7 @@ class Trace(Action):
         :param base_path: the path to the base directory in which to create the session directory
         :param events_ust: the list of ROS UST events to enable
         :param events_kernel: the list of kernel events to enable
+        :param profile_fast: `True` to use fast profiling, `False` for normal (only if necessary)
         """
         super().__init__(**kwargs)
         if append_timestamp:
@@ -59,8 +69,41 @@ class Trace(Action):
         self.__base_path = base_path
         self.__events_ust = events_ust
         self.__events_kernel = events_kernel
+        self.__ld_preload_action = None
+        if self.has_profiling_events(events_ust):
+            profile_lib_name = self.PROFILE_LIB_FAST if profile_fast else self.PROFILE_LIB_NORMAL
+            self.__ld_preload_action = SetEnvironmentVariable(
+                'LD_PRELOAD',
+                self.get_shared_lib_path(profile_lib_name),
+            )
+
+    @classmethod
+    def has_profiling_events(cls, events_ust: List[str]) -> bool:
+        matches = [re.match(cls.PROFILE_PATTERN, event_name) for event_name in events_ust]
+        return any(matches)
+
+    @staticmethod
+    def get_shared_lib_path(lib_name: str) -> Union[str, None]:
+        """
+        Get the full path to a given shared lib, if possible.
+
+        :param lib_name: the name of the shared library
+        :return: the full path if found, `None` otherwise
+        """
+        (exit_code, output) = subprocess.getstatusoutput(f'whereis -b {lib_name}')
+        if exit_code != 0:
+            return None
+        # Output of whereis is
+        # <input_lib_name>: <full path, if found>
+        # Filter out empty strings, in case lib is not found
+        output_split = [split_part for split_part in output.split(':') if len(split_part) > 0]
+        if len(output_split) != 2:
+            return None
+        return output_split[1].strip()
 
     def execute(self, context: LaunchContext) -> Optional[List[Action]]:
+        if self.__ld_preload_action is not None:
+            context.add_action(self.__ld_preload_action)
         # TODO make sure this is done as late as possible
         context.register_event_handler(OnShutdown(on_shutdown=self._destroy))
         # TODO make sure this is done as early as possible