linux-kernel - Re: [PATCH] perf record: Limit --intr-regs to platforms supporting PERF

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Date:	Tue, 29 Sep 2015 11:06:17 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	linuxppc-dev@...ts.ozlabs.org,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Subject: Re: [PATCH] perf record: Limit --intr-regs to platforms supporting
 PERF_REGS

On 2015/09/24 10:15PM, Naveen N Rao wrote:
> On 2015/09/24 08:32AM, Stephane Eranian wrote:
> > On Thu, Sep 24, 2015 at 5:57 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> > >
> > > On Thu, Sep 24, 2015 at 05:41:58PM +0530, Naveen N. Rao wrote:
> > > > perf build currently fails on powerpc:
> > > >
> > > >   LINK     perf
> > > > libperf.a(libperf-in.o):(.toc+0x120): undefined reference to
> > > > `sample_reg_masks'
> > > > libperf.a(libperf-in.o):(.toc+0x130): undefined reference to
> > > > `sample_reg_masks'
> > > > collect2: error: ld returned 1 exit status
> > > > make[1]: *** [perf] Error 1
> > > > make: *** [all] Error 2
> > > >
> > > > This is due to parse-regs-options.c using sample_reg_masks, which is
> > > > defined only with CONFIG_PERF_REGS.
> > > >
> > > > In addition, perf record -I is only useful if the arch supports
> > > > PERF_REGS. Hence, let's expose -I conditionally.
> > > >
> > > > Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> > >
> > > hum, I wonder why we have sample_reg_masks defined as weak in util/perf_regs.c
> > > which is also built only via CONFIG_PERF_REGS
> > >
> > > I wonder we could get rid of the weak definition via attached patch, Stephane?
> > >
> > But the whole point of having it weak is to avoid this error scenario
> > on any arch without support
> > and avoid ugly #ifdef HAVE_ in generic files.
> > 
> > if perf_regs.c is compiled on PPC, then why do we get the undefined?
> 
> As Jiri Olsa pointed out, powerpc and many other architectures don't 
> (yet) have support for perf regs.
> 
> But, the larger reason to introduce #ifdef is so the user doesn't see 
> options (s)he can't use on a specific architecture, along the same lines 
> as builtin-probe.c

Stephane, Arnaldo,
Suka has also posted a fix for this with a different approach [1]. Can 
you please ack/pull one of these versions? Building perf is broken on 
v4.3-rc due to this.

[1] http://article.gmane.org/gmane.linux.kernel/2046370

Thanks,
Naveen

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