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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

  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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