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>

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 99283b2dcfd6a93ec6c7ac1c843ec05ced17a76d..e1214b9dc9909729a51f1fb0474133cad6ee44fa 100644 (file)
--- a/kernel/trace/Kconfig
+++ b/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

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index dcb4e02afc5f493af4d33bb7e2f780897646a804..fc5dcc888e13a8f0cb9ab3fda0468eed01adcf14 100644 (file)
--- a/kernel/trace/Makefile
+++ b/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