linux-kernel - Re: [PATCH 3/3] tracing: Tracers that use CALLER_ADDR macros should select FRAME

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Message-ID: <c62985530902040726x34aeee7fr3b2937d898d3061e@mail.gmail.com>
Date:	Wed, 4 Feb 2009 16:26:15 +0100
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	Steven Rostedt <srostedt@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Paul Mackerras <paulus@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 3/3] tracing: Tracers that use CALLER_ADDR macros should 
	select FRAME_POINTER

2009/2/4 Anton Vorontsov <avorontsov@...mvista.com>:
> Irqsoff, switch and preempt tracers use CALLER_ADDR macros, so they
> should select FRAME_POINTER. Otherwise traces are meaningless.
>
> Signed-off-by: Anton Vorontsov <avorontsov@...mvista.com>
> ---
>  kernel/trace/Kconfig |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index e2a4ff6..48f7a37 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -86,6 +86,7 @@ config IRQSOFF_TRACER
>        select TRACE_IRQFLAGS
>        select TRACING
>        select TRACER_MAX_TRACE
> +       select FRAME_POINTER
>        help
>          This option measures the time spent in irqs-off critical
>          sections, with microsecond accuracy.
> @@ -108,6 +109,7 @@ config PREEMPT_TRACER
>        depends on DEBUG_KERNEL
>        select TRACING
>        select TRACER_MAX_TRACE
> +       select FRAME_POINTER
>        help
>          This option measures the time spent in preemption off critical
>          sections, with microsecond accuracy.
> @@ -136,6 +138,7 @@ config SCHED_TRACER
>        select TRACING
>        select CONTEXT_SWITCH_TRACER
>        select TRACER_MAX_TRACE
> +       select FRAME_POINTER
>        help
>          This tracer tracks the latency of the highest priority task
>          to be scheduled in, starting from the point it has woken up.
> --


Looks right.

BTW, how behaves builtin_return_address in case of !FRAME_POINTERS ?
I guess it would only work with the first caller builtin_return_address(0)
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