diff options
| author | Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-05-02 21:32:33 -0400 |
|---|---|---|
| committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-05-05 11:09:25 -0400 |
| commit | 6ce2c04fcbcaa5eb086e5142ab359be306cbc3e1 (patch) | |
| tree | e404fa564374277c40bff95682f3477de87fbae9 /Documentation/trace | |
| parent | 4f94559f40ad06d627c0fdfc3319cec778a2845b (diff) | |
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>
Diffstat (limited to 'Documentation/trace')
| -rw-r--r-- | Documentation/trace/ftrace.rst | 25 |
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 |