Re: [PATCH] perf record: Limit --intr-regs to platforms supporting PERF_REGS

[Naveen N. Rao]

On 2015/09/24 08:32AM, Stephane Eranian wrote:
> On Thu, Sep 24, 2015 at 5:57 AM, Jiri Olsa <jolsa@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> >
> > 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

Regards,
Naveen

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