From: Anton Vorontsov <avorontsov@ru.mvista.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <srostedt@redhat.com>,
Paul Mackerras <paulus@samba.org>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH v2] ftrace: On PowerPC we don't need frame pointers for CALLER_ADDRs
Date: Wed, 4 Feb 2009 18:07:55 +0300 [thread overview]
Message-ID: <20090204150755.GA24163@oksana.dev.rtsoft.ru> (raw)
In-Reply-To: <20090203161955.GA776@oksana.dev.rtsoft.ru>
On Tue, Feb 03, 2009 at 07:19:55PM +0300, Anton Vorontsov wrote:
> On Tue, Feb 03, 2009 at 05:06:45PM +0100, Ingo Molnar wrote:
> >
> > * Anton Vorontsov <avorontsov@ru.mvista.com> 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. [...]
> >
> > hm, why not add PPC to FRAME_POINTERS list of architectures, and select it
> > from the powerpc arch Kconfig? Does that cause complications somewhere?
>
> -fno-omit-frame-pointers makes the code worse w/o any actual
> benefit that we would use. Plus, there is a long standing bug in
> gcc that makes -fno-omit-frame-pointer generate wrong code for PPC
> targets:
>
> http://lkml.org/lkml/2008/9/2/25
>
> That is, the only tracer that needs[1] -fno-omit-frame-pointer is
> "FUNCTION_TRCER", but we workaround the issue via -mno-sched-epilog,
> quoting arch/powerpc/Makefile:
>
> # Work around a gcc code-gen bug with -fno-omit-frame-pointer.
> ifeq ($(CONFIG_FUNCTION_TRACER),y)
> KBUILD_CFLAGS += -mno-sched-epilog
> endif
Thinking about it more... we can workaround the bug the other way,
and then permit CONFIG_FRAME_POINTER on PowerPC.
Patches are coming...
--
Anton Vorontsov
email: cbouatmailru@gmail.com
irc://irc.freenode.net/bd2
next prev parent reply other threads:[~2009-02-04 15:07 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-31 19:06 [PATCH] ftrace: On PowerPC we don't need frame pointers for CALLER_ADDRs Anton Vorontsov
2009-02-02 0:35 ` Benjamin Herrenschmidt
2009-02-02 14:04 ` Steven Rostedt
2009-02-03 14:56 ` [PATCH v2] " Anton Vorontsov
2009-02-03 16:06 ` Ingo Molnar
2009-02-03 16:19 ` Anton Vorontsov
2009-02-03 16:32 ` Steven Rostedt
2009-02-03 18:59 ` Anton Vorontsov
2009-02-04 0:34 ` Benjamin Herrenschmidt
2009-02-04 15:07 ` Anton Vorontsov [this message]
2009-02-04 15:08 ` [PATCH 1/3] Makefile: Include arch Makefiles as late as possible Anton Vorontsov
2009-02-04 21:26 ` Ingo Molnar
2009-02-11 3:51 ` Benjamin Herrenschmidt
2009-02-11 13:23 ` Ingo Molnar
2009-02-11 14:11 ` Steven Rostedt
2009-02-14 19:58 ` Sam Ravnborg
2009-02-14 19:57 ` Sam Ravnborg
2009-02-14 22:03 ` Ingo Molnar
2009-02-15 0:19 ` Benjamin Herrenschmidt
2009-02-15 8:09 ` Ingo Molnar
2009-02-16 14:20 ` Anton Vorontsov
2009-02-16 14:53 ` Anton Vorontsov
2009-02-16 20:04 ` Sam Ravnborg
2009-02-16 16:08 ` Anton Vorontsov
2009-02-16 17:22 ` Ingo Molnar
2009-02-04 15:08 ` [PATCH 2/3] powerpc: Make it possible to safely select CONFIG_FRAME_POINTER Anton Vorontsov
2009-02-05 0:31 ` Benjamin Herrenschmidt
2009-02-05 0:35 ` Steven Rostedt
2009-02-05 1:12 ` Anton Vorontsov
2009-02-05 1:15 ` Benjamin Herrenschmidt
2009-02-05 1:30 ` Anton Vorontsov
2009-02-05 15:45 ` Anton Vorontsov
2009-02-04 15:08 ` [PATCH 3/3] tracing: Tracers that use CALLER_ADDR macros should select FRAME_POINTER Anton Vorontsov
2009-02-04 15:26 ` Frédéric Weisbecker
2009-02-04 15:31 ` Steven Rostedt
2009-02-04 15:36 ` Anton Vorontsov
2009-02-04 16:50 ` Frédéric Weisbecker
2009-02-04 8:17 ` [PATCH v2] ftrace: On PowerPC we don't need frame pointers forCALLER_ADDRs Usha Rani Konudula
2009-02-04 8:37 ` Usha Rani Konudula
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