linux-kernel - Re: [PATCH v2 1/2] perf: Move arch specific code into separate arch directory

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Message-ID: <20100414170008.GA2359@osiris.boeblingen.de.ibm.com>
Date:	Wed, 14 Apr 2010 19:00:08 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ian Munsie <imunsie@....ibm.com>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, benh@...nel.crashing.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH v2 1/2] perf: Move arch specific code into separate
 arch directory

On Wed, Apr 14, 2010 at 07:46:12AM -0700, Masami Hiramatsu wrote:
> Ian Munsie wrote:
> > From: Ian Munsie <imunsie@...ibm.com>
> > 
> > The perf userspace tool included some architecture specific code to map
> > registers from the DWARF register number into the names used by the regs
> > and stack access API.
> > 
> > This patch moves the architecture specific code out into a separate
> > arch/x86 directory along with the infrastructure required to use it.
> > 
> > Signed-off-by: Ian Munsie <imunsie@...ibm.com>
> > ---
> > Changes since v1: From Masami Hiramatsu's suggestion, I added a check in the
> > Makefile for if the arch specific Makefile defines PERF_HAVE_DWARF_REGS,
> > printing a message during build if it has not. This simplifies the code
> > removing the odd macro from the previous version and the need for an arch
> > specific arch_dwarf-regs.h. I have not entirely disabled DWARF support for
> > architectures that don't implement the register mappings, so that they can
> > still add a probe based on a line number (they will be missing the ability to
> > capture the value of a variable from a register).
> 
> Hmm, sorry, I don't think it is a good way to go... IMHO, porting dwarf-regs.c
> is so easy (you can just refer systemtap/runtime/loc2c-runtime.h), easier
> than porting kprobe-tracer on another arch. And perf is a part of kernel tree.
> It means that someone who are porting kprobe-tracer, he should port
> dwarf-regs.c too. In that case, PERF_HAVE_DWARF_REGS flag will be used only
> between those two patches in same patchset. So, I suggested you to drop dwarf
> support if dwarf-regs mapping doesn't exist.
> 
> AFAIK, at this point, only s390 users are affected. I'd like to ask
> them to just port a register mapping on perf and test it too.

Hm, I'm a bit lost here. Probably due to lack of context. What would be missing
on s390 and what am I supposed to implement and how can I test it?
Any pointers to git commits?
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