Re: [PATCH v1 07/11] perf probe: Move elfutils support check to libdw check

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Sep 26, 2024 at 08:08:22AM -0700, Ian Rogers wrote:
> On Wed, Sep 25, 2024 at 5:30 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > On Tue, Sep 24, 2024 at 09:04:14AM -0700, Ian Rogers wrote:
> > > The test _ELFUTILS_PREREQ(0, 142) is false for elfutils before
> > > 2009-06-13, but that is 15 years ago and very unlikely. Add a test to
> > > test-libdw.c and assume the libdw version is at least 0.142 to
> > > simplify the build logic.
> > >
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
> > >  tools/build/feature/test-libdw.c | 10 +++++++++-
> > >  tools/perf/util/probe-finder.c   |  2 --
> > >  tools/perf/util/probe-finder.h   |  2 --
> > >  3 files changed, 9 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/tools/build/feature/test-libdw.c b/tools/build/feature/test-libdw.c
> > > index 71c6f8e3b0ee..2fb59479ab77 100644
> > > --- a/tools/build/feature/test-libdw.c
> > > +++ b/tools/build/feature/test-libdw.c
> > > @@ -41,8 +41,16 @@ int test_libdw_getcfi(void)
> > >       return dwarf_getcfi(dwarf) == NULL;
> > >  }
> > >
> > > +int test_elfutils(void)
> > > +{
> > > +     Dwarf_CFI *cfi = NULL;
> > > +
> > > +     dwarf_cfi_end(cfi);
> > > +     return 0;
> > > +}
> >
> > I think it's the same as test_libdw_getcfi() and let's get rid of it.
> 
> The point of doing the change this way, and I think what's being
> ignored, is that I am trying to simply replace an #if with a clearly
> equivalent feature test - clearly equivalent as the #if guards use of
> dwarf_cfi_end in the code. Merging test_elfutils with
> test_libdw_getcfi is another cognitive step and I think it is fine as
> follow up cleanup. Combining that step with the change here fails the
> minimal meaningful change and tbh I think this is just bike shedding.

Ok, I think it's ok to have a separate commit to combine equivalent
tests if you really want to.  What I want in the end is not to have
unnecessary or duplicate code.

In order to have a clearly equivalent feature test, I think you can add

  #if !_ELFUTILS_PREREQ(0, 142)
  #error "elfutils version is too old"
  #endif

Thanks,
Namhyung

> >
> > > +
> > >  int main(void)
> > >  {
> > >       return test_libdw() + test_libdw_unwind() + test_libdw_getlocations() +
> > > -            test_libdw_getcfi();
> > > +            test_libdw_getcfi() + test_elfutils();
> > >  }
> > > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> > > index 78f34fa0c391..7434b38596b9 100644
> > > --- a/tools/perf/util/probe-finder.c
> > > +++ b/tools/perf/util/probe-finder.c
> > > @@ -1379,10 +1379,8 @@ int debuginfo__find_trace_events(struct debuginfo *dbg,
> > >       if (ret >= 0 && tf.pf.skip_empty_arg)
> > >               ret = fill_empty_trace_arg(pev, tf.tevs, tf.ntevs);
> > >
> > > -#if _ELFUTILS_PREREQ(0, 142)
> > >       dwarf_cfi_end(tf.pf.cfi_eh);
> > >       dwarf_cfi_end(tf.pf.cfi_dbg);
> > > -#endif
> > >
> > >       if (ret < 0 || tf.ntevs == 0) {
> > >               for (i = 0; i < tf.ntevs; i++)
> > > diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h
> > > index 3add5ff516e1..f0149d72310c 100644
> > > --- a/tools/perf/util/probe-finder.h
> > > +++ b/tools/perf/util/probe-finder.h
> > > @@ -63,12 +63,10 @@ struct probe_finder {
> > >       struct intlist          *lcache;        /* Line cache for lazy match */
> > >
> > >       /* For variable searching */
> > > -#if _ELFUTILS_PREREQ(0, 142)
> > >       /* Call Frame Information from .eh_frame */
> > >       Dwarf_CFI               *cfi_eh;
> > >       /* Call Frame Information from .debug_frame */
> > >       Dwarf_CFI               *cfi_dbg;
> > > -#endif
> > >       Dwarf_Op                *fb_ops;        /* Frame base attribute */
> > >       unsigned int            machine;        /* Target machine arch */
> > >       struct perf_probe_arg   *pvar;          /* Current target variable */
> > > --
> > > 2.46.0.792.g87dc391469-goog
> > >