ftrace: Allow tracing of some of the tracing code

There is times when tracing the tracing infrastructure can be useful for
debugging the tracing code. Currently all files in the tracing directory
are set to "notrace" the functions.

Add a new config option FUNCTION_SELF_TRACING that will allow some of the
files in the tracing infrastructure to be traced. It requires a config to
enable because it will add noise to the function tracer if events and
other tracing features are enabled. Tracing functions and events together
is quite common, so not tracing the event code should be the default.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Link: https://patch.msgid.link/20251120181514.736f2d5f@gandalf.local.home
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

kernel/trace/Kconfig

@@ -330,6 +330,20 @@ config DYNAMIC_FTRACE_WITH_ARGS
 	depends on DYNAMIC_FTRACE
 	depends on HAVE_DYNAMIC_FTRACE_WITH_ARGS
 
+config FUNCTION_SELF_TRACING
+	bool "Function trace tracing code"
+	depends on FUNCTION_TRACER
+	help
+	  Normally all the tracing code is set to notrace, where the function
+	  tracer will ignore all the tracing functions. Sometimes it is useful
+	  for debugging to trace some of the tracing infratructure itself.
+	  Enable this to allow some of the tracing infrastructure to be traced
+	  by the function tracer. Note, this will likely add noise to function
+	  tracing if events and other tracing features are enabled along with
+	  function tracing.
+
+	  If unsure, say N.
+
 config FPROBE
 	bool "Kernel Function Probe (fprobe)"
 	depends on HAVE_FUNCTION_GRAPH_FREGS && HAVE_FTRACE_GRAPH_FUNC

kernel/trace/Makefile

@@ -16,6 +16,23 @@ obj-y += trace_selftest_dynamic.o
 endif
 endif
 
+# Allow some files to be function traced
+ifdef CONFIG_FUNCTION_SELF_TRACING
+CFLAGS_trace_output.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_seq.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_stat.o = $(CC_FLAGS_FTRACE)
+CFLAGS_tracing_map.o = $(CC_FLAGS_FTRACE)
+CFLAGS_synth_event_gen_test.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_events.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_syscalls.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_events_filter.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_events_trigger.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_events_synth.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_events_hist.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_events_user.o = $(CC_FLAGS_FTRACE)
+CFLAGS_trace_dynevent.o = $(CC_FLAGS_FTRACE)
+endif
+
 ifdef CONFIG_FTRACE_STARTUP_TEST
 CFLAGS_trace_kprobe_selftest.o = $(CC_FLAGS_FTRACE)
 obj-$(CONFIG_KPROBE_EVENTS) += trace_kprobe_selftest.o