Re: [PATCH] ftrace/microblaze: Do not find "true_parent" for return address

[Steven Rostedt <rostedt@goodmis.org>]

[ Added Jeff ]

-- Steve

On Wed, 11 Dec 2024 15:36:34 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> When function tracing and function graph tracing are both enabled (in
> different instances) the "parent" of some of the function tracing events
> is "return_to_handler" which is the trampoline used by function graph
> tracing. To fix this, ftrace_get_true_parent_ip() was introduced that
> returns the "true" parent ip instead of the trampoline.
> 
> To do this, the ftrace_regs_get_stack_pointer() is used, which uses
> kernel_stack_pointer(). The problem is that microblaze does not implement
> kerenl_stack_pointer() so when function graph tracing is enabled, the
> build fails.
> 
> Modify the #ifdef check to the code around ftrace_get_true_parent_ip() to
> include !defined(CONFIG_MICROBLAZE) which will default it to just return
> the parent ip passed in, which may still be the ip of the function garph
> trampoline.
> 
> Fixes: 60b1f578b578 ("ftrace: Get the true parent ip for function tracer")
> Reported-by: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/trace_functions.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> index 74c353164ca1..a75d107a45f8 100644
> --- a/kernel/trace/trace_functions.c
> +++ b/kernel/trace/trace_functions.c
> @@ -176,7 +176,8 @@ static void function_trace_start(struct trace_array *tr)
>  	tracing_reset_online_cpus(&tr->array_buffer);
>  }
>  
> -#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +/* Microblaze currently doesn't implement kernel_stack_pointer() */
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && !defined(CONFIG_MICROBLAZE)
>  static __always_inline unsigned long
>  function_get_true_parent_ip(unsigned long parent_ip, struct ftrace_regs *fregs)
>  {