Re: [PATCH 6/6] ARM: ftrace: enable function graph tracer

[Rabin Vincent]

On Mon, Nov 08, 2010 at 10:42:57AM +0000, Catalin Marinas wrote:
> 2010/11/8 Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>:
> > On Sat, Nov 06, 2010 at 07:06:28PM +0000, Catalin Marinas wrote:
> >> On Saturday, November 6, 2010, Rabin Vincent <rabin@xxxxxx> wrote:
> >> > --- 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.
> 
> If a precondition for FRAME_POINTER isn't true, we should not force it
> via 'select'. We try to get rid of such warnings in the kernel.
> 
> However, on ARM the FRAME_POINTER depends on !THUMB2_KERNEL but for
> Thumb-2 kernels HAVE_FUNCTION_GRAPH_TRACER is also disabled, so there
> isn't a dependency issue here. It's more like a personal preference to
> keep the changes within the arch/arm tree.

OK, new patch below.