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

["Frédéric Weisbecker" <fweisbec@gmail.com>]

2008/11/25 Steven Rostedt <rostedt@goodmis.org>:
> From: Steven Rostedt <rostedt@goodmis.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@redhat.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@gmail.com>