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

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Message-ID: <ZvbocHwtPkwJwDOA@google.com>
Date: Fri, 27 Sep 2024 10:16:32 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
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	Yang Jihong <yangjihong@...edance.com>
Subject: Re: [PATCH v1 11/11] perf build: Rename PERF_HAVE_DWARF_REGS to
 PERF_HAVE_LIBDW_REGS

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.

Thanks,
Namhyung