linux-kernel - Re: [PATCH] ftrace: Hide a extra entry in stack trace

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Message-ID: <20240926010536.5fe73463@rorschach.local.home>
Date: Thu, 26 Sep 2024 01:05:36 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Tatsuya S <tatsuya.s2862@...il.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: Hide a extra entry in stack trace

On Mon, 23 Sep 2024 12:59:15 +0900
Tatsuya S <tatsuya.s2862@...il.com> wrote:

> A extra entry is shown on stack trace(CONFIG_UNWINDER_ORC=y).
> 
>     [003] .....   110.171589: vfs_write <-__x64_sys_write
>     [003] .....   110.171600: <stack trace>
>  => XXXXXXXXX (Wrong function name)
>  => vfs_write
>  => __x64_sys_write
>  => do_syscall_64
>  => entry_SYSCALL_64_after_hwframe  
> 
> To resolve this, increment skip in __ftrace_trace_stack().
> The reason why skip is incremented in __ftrace_trace_stack()
> is because __ftrace_trace_stack() in stack trace is the only function
> that wasn't skipped from anywhere.
> 
> Signed-off-by: Tatsuya S <tatsuya.s2862@...il.com>
> ---
>  kernel/trace/trace.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c3b2c7dfadef..e0d98621ff23 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2919,6 +2919,8 @@ static void __ftrace_trace_stack(struct trace_buffer *buffer,
>  #ifndef CONFIG_UNWINDER_ORC
>  	if (!regs)
>  		skip++;
> +#else
> +	skip++;
>  #endif

The above #ifdef block should be removed and replaced with;


	if (IS_ENABLED(CONFIG_UNWINDER_ORC) || !regs)
		skip++;

>  
>  	preempt_disable_notrace();

-- Steve