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

[Ian Rogers]

On Wed, Sep 25, 2024 at 5:30 PM Namhyung Kim <namhyung@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >  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.

Thanks,
Ian

> 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
> >