linux-kernel - Ftrace: Static function graph not work

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Date:   Thu, 23 Mar 2017 11:28:03 +0800
From:   Zong Li <zongbox@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: Ftrace: Static function graph not work

Hi all,

I test the static function graph for ARM, x86 and x86_64 architecture
on linux-3.10 and linux-4.9, and I find it works correctly only for
x86_64 on linux-4.9.

After the following commit, the function tracer also be registered
when registering the function graph tracer.

commit 2940c25bec92f40a3f7f32504b8ea115d1701892
Author:     Steven Rostedt (Red Hat) <rostedt@...dmis.org>
CommitDate: Wed Dec 4 10:57:05 2013 -0800

    ftrace: Fix function graph with loading of modules

The arch-depend code implement the mcount function pseudo code like:

void mcount(void)
{
        ...
        if (ftrace_trace_function != ftrace_stub)
                goto do_trace;

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
       if (ftrace_graph_return != ftrace_stub ||
           ftrace_graph_entry != ftrace_graph_entry_stub)
               ftrace_graph_caller();
#endif
        return;

do_trace:
        ...
}

The function pointer 'ftrace_trace_function' will not be 'ftrace_stub'
because function tracer is registered too, so the function graph part
will not be executed.

On the other hand, I find the another patch to resolve this situation,
and it is reason that x86_64 architecture can work correctly.

commit 62a207d748dd9224140a634786b274fdb6ece0b9
Author:     Steven Rostedt (Red Hat) <rostedt@...dmis.org>
CommitDate: Mon Nov 24 15:02:25 2014 -0500

    ftrace/x86: Have static function tracing always test for function graph

so, is this problem tending to handle by each architecture? or maybe
it is need to solve by generic code?

This is my first mail to mailing list, please excuse having mistake
and let me know.
Thank a lot !