ftrace: Add MODIFIED flag to show if IPMODIFY or direct was attached

If a function had ever had IPMODIFY or DIRECT attached to it, where this
is how live kernel patching and BPF overrides work, mark them and display
an "M" in the enabled_functions and touched_functions files. This can be
used for debugging. If a function had been modified and later there's a bug
in the code related to that function, this can be used to know if the cause
is possibly from a live kernel patch or a BPF program that changed the
behavior of the code.

Also update the documentation on the enabled_functions and
touched_functions output, as it was missing direct callers and CALL_OPS.
And include this new modify attribute.

Link: https://lore.kernel.org/linux-trace-kernel/20230502213233.004e3ae4@gandalf.local.home

Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index aaebb821912e..d5766229c71a 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -350,6 +350,19 @@ of ftrace. Here is a list of some of the key files:
 	an 'I' will be displayed on the same line as the function that
 	can be overridden.
 
+	If a non ftrace trampoline is attached (BPF) a 'D' will be displayed.
+	Note, normal ftrace trampolines can also be attached, but only one
+	"direct" trampoline can be attached to a given function at a time.
+
+	Some architectures can not call direct trampolines, but instead have
+	the ftrace ops function located above the function entry point. In
+	such cases an 'O' will be displayed.
+
+	If a function had either the "ip modify" or a "direct" call attached to
+	it in the past, a 'M' will be shown. This flag is never cleared. It is
+	used to know if a function was every modified by the ftrace infrastructure,
+	and can be used for debugging.
+
 	If the architecture supports it, it will also show what callback
 	is being directly called by the function. If the count is greater
 	than 1 it most likely will be ftrace_ops_list_func().
@@ -359,6 +372,18 @@ of ftrace. Here is a list of some of the key files:
 	its address will be printed as well as the function that the
 	trampoline calls.
 
+  touched_functions:
+
+	This file contains all the functions that ever had a function callback
+	to it via the ftrace infrastructure. It has the same format as
+	enabled_functions but shows all functions that have every been
+	traced.
+
+	To see any function that has every been modified by "ip modify" or a
+	direct trampoline, one can perform the following command:
+
+	grep ' M ' /sys/kernel/tracing/touched_functions
+
   function_profile_enabled:
 
 	When set it will enable all functions with either the function