linux-kernel - Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry is used

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Date:	Wed, 08 Aug 2012 13:34:51 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC PATCH 3/4] ftrace: Do not test frame pointers if -mfentry
 is used

(2012/08/08 4:38), Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> The function graph has a test to check if the frame pointer is
> corrupted, which can happen with various options of gcc with mcount.
> But this is not an issue with -mfentry as -mfentry does not need nor use
> frame pointers for function graph tracing.
> 
> Cc: Andi Kleen <andi@...stfloor.org>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  kernel/trace/trace_functions_graph.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index ce27c8b..99b4378 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -143,7 +143,7 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
>  		return;
>  	}
>  
> -#ifdef CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST
> +#if defined(CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST) && !defined(CC_USING_FENTRY)

I think CONFIG_HAVE_FENTRY would better unselect
CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST in arch/x86/Kconfig explicitly.

Thank you,


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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