From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 674A4DDF40 for ; Mon, 2 Feb 2009 11:35:39 +1100 (EST) Subject: Re: [PATCH] ftrace: On PowerPC we don't need frame pointers for CALLER_ADDRs From: Benjamin Herrenschmidt To: Anton Vorontsov In-Reply-To: <20090131190650.GA4284@oksana.dev.rtsoft.ru> References: <20090131190650.GA4284@oksana.dev.rtsoft.ru> Content-Type: text/plain Date: Mon, 02 Feb 2009 11:35:19 +1100 Message-Id: <1233534919.18767.69.camel@pasglop> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, Steven Rostedt , Paul Mackerras , Ingo Molnar , linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, 2009-01-31 at 22:06 +0300, Anton Vorontsov wrote: > According to this discussion: > > http://lkml.org/lkml/2008/7/25/338 > http://lkml.org/lkml/2008/7/26/72 > > Frame pointers do nothing useful on PowerPC, so lib/Kconfig.debug > makes CONFIG_FRAME_POINTER unselectable on PPC targets. But ftrace.h > requires CONFIG_FRAME_POINTER for CALLER_ADDR macros. Therefore > tracing is completely useless on PowerPC: But we need them for -pg which ftrace uses no ? (ie, gcc forces you to have -fno-omit-frame-pointers with -fpg iirc). Now, regardless, I agree that on PPC, __builtin_return_address() should always work with our without that cruft, so we may as well apply that patch... > [...] > -0 0X.h3 2us+: 0:140:R + [000] 1733:120:S mvtsd > -0 0X.h3 9us+: 0 (0) > -0 0X..3 72us : 0 (0) > -0 0X..3 73us : 0:140:R ==> [000] 1733:120:R mvtsd > > On PPC we can safely use __builtin_return_address(1..6) w/o frame > pointers, and with this patch the trace output looks OK: > > [...] > -0 0X.h3 2us+: 0:140:R + [000] 1740:120:S mvtsd > -0 0X.h3 9us+: hrtimer_wakeup (__run_hrtimer) > -0 0X..3 87us : cpu_idle (__got2_end) > -0 0X..3 89us : 0:140:R ==> [000] 1740:120:R mvtsd > > Signed-off-by: Anton Vorontsov > --- > > Btw, on PowerPC tracing is also broken w/o "ring-buffer: fix alignment > problem" patch (currently collecting dust in the -tip tree, commit > 082605de5f82eb692cc90f7fda071cc01bb5ac34). Any chance the fix go into > Linus' tree, to not waste other people's time bisecting and debugging > the problem? ;-) > > For google: tracing, regression, "ring-buffer: move some metadata > into buffer page", commit abc9b56d66fbd4d93302ef4bf6fa726e1b8255f9, > answer is here. > > include/linux/ftrace.h | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 9c5bc6b..13eba02 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -146,7 +146,7 @@ static inline void __ftrace_enabled_restore(int enabled) > #endif > } > > -#ifdef CONFIG_FRAME_POINTER > +#if defined(CONFIG_FRAME_POINTER) || defined(CONFIG_PPC) > /* TODO: need to fix this for ARM */ > # define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0)) > # define CALLER_ADDR1 ((unsigned long)__builtin_return_address(1))