From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Mon, 8 Nov 2010 10:42:57 +0000 Subject: [PATCH 6/6] ARM: ftrace: enable function graph tracer In-Reply-To: <20101108091858.GP16938@pengutronix.de> References: <1289067954-5080-1-git-send-email-rabin@rab.in> <1289067954-5080-6-git-send-email-rabin@rab.in> <20101108091858.GP16938@pengutronix.de> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 2010/11/8 Uwe Kleine-K?nig : > On Sat, Nov 06, 2010 at 07:06:28PM +0000, Catalin Marinas wrote: >> On Saturday, November 6, 2010, Rabin Vincent 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. 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. -- Catalin