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    SubjectRe: [PATCH 6/6] ARM: ftrace: enable function graph tracer
    On Sat, Nov 06, 2010 at 07:06:28PM +0000, Catalin Marinas wrote:
    > On Saturday, November 6, 2010, Rabin Vincent <rabin@rab.in> wrote:
    > > Add the options to enable the function graph tracer on ARM.  Function
    > > graph tracer support requires frame pointers, so exclude Thumb-2 and
    > > also explicitly select FRAME_POINTER in FUNCTION_GRAPH_TRACER since
    > > FUNCTION_TRACER doesn't select FRAME_POINTER when ARM_UNWIND is used
    > > Therefore, with GCC 4.4.0+, you get plain function tracing without frame
    > > pointers, but you'll need them if you want function graph tracing.
    > .....
    > > --- a/kernel/trace/Kconfig
    > > +++ b/kernel/trace/Kconfig
    > > @@ -141,6 +141,7 @@ config FUNCTION_TRACER
    > >
    > >  config FUNCTION_GRAPH_TRACER
    > >        bool "Kernel Function Graph Tracer"
    > > +       select FRAME_POINTER if ARM_UNWIND
    >
    > Would it be better to modify FRAME_POINTER definition in the ARM
    > Kconfig so that it is enabled automatically when FUNCTION_GRAPH_TRACER
    > is enabled?
    I don't like that suggestion much because it hides the dependency.
    Moreover a "default y if FUNCTION_GRAPH_TRACER" doesn't work if a
    precondition for FRAME_POINTER isn't true. Rabin's approach at least
    generates a warning.

    Best regards
    Uwe

    --
    Pengutronix e.K. | Uwe Kleine-König |
    Industrial Linux Solutions | http://www.pengutronix.de/ |
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