linux-kernel - Re: [PATCH 2/3] ftrace: use code patching for ftrace return tracer

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Date:	Wed, 26 Nov 2008 01:13:04 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, "Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Steven Rostedt" <srostedt@...hat.com>
Subject: Re: [PATCH 2/3] ftrace: use code patching for ftrace return tracer

2008/11/25 Steven Rostedt <rostedt@...dmis.org>:
> From: Steven Rostedt <rostedt@...dmis.org>
>
> Impact: more efficient code for ftrace return tracer
>
> This patch uses the dynamic patching, when available, to patch
> the function return code into the kernel.
>
> This patch will ease the way for letting both function tracing
> and function return tracing run together.
>
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
>  arch/x86/kernel/entry_32.S |    5 ++++
>  arch/x86/kernel/ftrace.c   |   46 +++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/ftrace.h     |    5 ++++
>  kernel/trace/ftrace.c      |   34 ++++++++++++++------------------
>  4 files changed, 70 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> index 7a934c0..d6f0333 100644
> --- a/arch/x86/kernel/entry_32.S
> +++ b/arch/x86/kernel/entry_32.S
> @@ -1185,6 +1185,11 @@ ftrace_call:
>        popl %edx
>        popl %ecx
>        popl %eax
> +#ifdef CONFIG_FUNCTION_RET_TRACER
> +.globl ftrace_return_call
> +ftrace_return_call:
> +       jmp ftrace_stub
> +#endif


And you patch ftrace_stub to ftrace_return_caller.
I see...
Seems a good idea :-)

Acked-by: Frederic Weisbecker <fweisbec@...il.com>
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