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

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Date:	Wed, 14 Apr 2010 07:46:12 -0700
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ian Munsie <imunsie@....ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>
CC:	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

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.

Thank you,

-- 
Masami Hiramatsu
e-mail: mhiramat@...hat.com
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