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

[Masami Hiramatsu <mhiramat@redhat.com>]

Ian Munsie wrote:
> From: Ian Munsie <imunsie@au.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@au.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@redhat.com