linux-kernel - Re: [PATCH v1 11/11] perf build: Rename PERF_HAVE_DWARF_REGS to PERF_HAVE_LIBDW

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Message-ID: <CAP-5=fWn6ejdozTt8GHvDkv-QW_GF5+b4C3kTO_544H-fXZ+0w@mail.gmail.com>
Date: Fri, 27 Sep 2024 11:15:21 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>, 
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	Leo Yan <leo.yan@...ux.dev>, Guo Ren <guoren@...nel.org>, 
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	Albert Ou <aou@...s.berkeley.edu>, Nick Terrell <terrelln@...com>, 
	Guilherme Amadio <amadio@...too.org>, Changbin Du <changbin.du@...wei.com>, 
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	Przemek Kitszel <przemyslaw.kitszel@...el.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, Yang Jihong <yangjihong@...edance.com>
Subject: Re: [PATCH v1 11/11] perf build: Rename PERF_HAVE_DWARF_REGS to PERF_HAVE_LIBDW_REGS

On Fri, Sep 27, 2024 at 10:16 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Thu, Sep 26, 2024 at 12:55:18PM -0700, Ian Rogers wrote:
> > On Thu, Sep 26, 2024 at 12:40 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > >
> > > On Thu, Sep 26, 2024 at 05:47:16AM -0700, Ian Rogers wrote:
> > > > On Wed, Sep 25, 2024 at 8:27 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > > > >
> > > > > On Tue, Sep 24, 2024 at 09:04:18AM -0700, Ian Rogers wrote:
> > > > > > The name dwarf can imply libunwind support, whereas
> > > > > > PERF_HAVE_DWARF_REGS is only enabled with libdw support. Rename to
> > > > > > make it clearer there is a libdw connection.
> > > > >
> > > > > While it only covers libdw, I think the idea of this macro is whether
> > > > > the arch has register mappings defined in DWARF standard.  So I think
> > > > > it's better to keep the name for this case.
> > > >
> > > > How can the dwarf standard exist for an arch but not define registers?
> > >
> > > I meant it's about the arch code in the perf tools to have the mapping,
> > > not the DWARF standard itself.
> >
> > But we guard those definitions behind having libdw:
> > https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/arch/x86/Makefile?h=perf-tools-next#n3
> > So we only have the regs if libdw is present, not if dwarf is in use
> > for libunwind/libdw. Hence wanting to be specific that they are just a
> > libdw and not a dwarf thing. Trying to use the regs in libunwind code
> > would be broken. That could change but I wanted to make the code clear
> > for the way things are at the moment.
>
> I understand your point but calling it LIBDW_REGS looks unnatural to me.

I don't follow. Wouldn't it be unnatural to see PERF_HAVE_DWARF_REGS
in libunwind code but you are to some how know that the code only had
meaning if libdw was present? I don't like the implication that DWARF
means LIBDW as throughout the code it doesn't. I think the name
PERF_HAVE_LIBDW_REGS better captures how the code is, makes the code
more intention revealing and so readable, etc.

Thanks,
Ian