Re: [PATCH v1 11/11] perf build: Rename PERF_HAVE_DWARF_REGS to PERF_HAVE_LIBDW_REGS

[Ian Rogers]

On Fri, Sep 27, 2024 at 10:16 AM Namhyung Kim <namhyung@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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