linux-kernel - Re: [for-linus][PATCH 3/3] ftrace/microblaze: Do not find "true

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Message-ID: <eb7933ae-3462-49de-b76d-16ca652d714e@monstr.eu>
Date: Fri, 13 Dec 2024 16:39:29 +0100
From: Michal Simek <monstr@...str.eu>
To: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [for-linus][PATCH 3/3] ftrace/microblaze: Do not find
 "true_parent" for return address



On 12/13/24 16:26, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
> 
> When function tracing and function graph tracing are both enabled (in
> different instances) 

What does this mean different instances? Two processes or two cores?


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

here is typo.

> trampoline.
> 
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Al Viro <viro@...IV.linux.org.uk>
> Cc: Michal Simek <monstr@...str.eu>
> Link: https://lore.kernel.org/20241211153634.69c75afa@batman.local.home
> Fixes: 60b1f578b578 ("ftrace: Get the true parent ip for function tracer")
> Reported-by: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.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() */

Does it mean that this function should depends on ARCH_HAS_CURRENT_STACK_POINTER 
instead of name the architecture?


> +#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)
>   {

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Xilinx Microblaze
Maintainer of Linux kernel - Xilinx Zynq ARM and ZynqMP/Versal ARM64 SoCs
U-Boot custodian - Xilinx Microblaze/Zynq/ZynqMP/Versal/Versal NET SoCs
TF-A maintainer - Xilinx ZynqMP/Versal/Versal NET SoCs