Re: [PATCH bpf-next] selftests/bpf: make use of PROCMAP_QUERY ioctl if available

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Aug 23, 2024 at 09:53:03AM -0700, Andrii Nakryiko wrote:
> On Fri, Aug 23, 2024 at 7:48 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Aug 7, 2024 at 8:17 AM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> > >
> > > On Wed, Aug 7, 2024 at 2:07 AM Jiri Olsa <olsajiri@gmail.com> wrote:
> > > >
> > > > On Tue, Aug 06, 2024 at 04:03:19PM -0700, Andrii Nakryiko wrote:
> > > >
> > > > SNIP
> > > >
> > > > >  ssize_t get_uprobe_offset(const void *addr)
> > > > >  {
> > > > > -     size_t start, end, base;
> > > > > -     char buf[256];
> > > > > -     bool found = false;
> > > > > +     size_t start, base, end;
> > > > >       FILE *f;
> > > > > +     char buf[256];
> > > > > +     int err, flags;
> > > > >
> > > > >       f = fopen("/proc/self/maps", "r");
> > > > >       if (!f)
> > > > >               return -errno;
> > > > >
> > > > > -     while (fscanf(f, "%zx-%zx %s %zx %*[^\n]\n", &start, &end, buf, &base) == 4) {
> > > > > -             if (buf[2] == 'x' && (uintptr_t)addr >= start && (uintptr_t)addr < end) {
> > > > > -                     found = true;
> > > > > -                     break;
> > > > > +     /* requested executable VMA only */
> > > > > +     err = procmap_query(fileno(f), addr, PROCMAP_QUERY_VMA_EXECUTABLE, &start, &base, &flags);
> > > > > +     if (err == -EOPNOTSUPP) {
> > > > > +             bool found = false;
> > > > > +
> > > > > +             while (fscanf(f, "%zx-%zx %s %zx %*[^\n]\n", &start, &end, buf, &base) == 4) {
> > > > > +                     if (buf[2] == 'x' && (uintptr_t)addr >= start && (uintptr_t)addr < end) {
> > > > > +                             found = true;
> > > > > +                             break;
> > > > > +                     }
> > > > > +             }
> > > > > +             if (!found) {
> > > > > +                     fclose(f);
> > > > > +                     return -ESRCH;
> > > > >               }
> > > > > +     } else if (err) {
> > > > > +             fclose(f);
> > > > > +             return err;
> > > >
> > > > I feel like I commented on this before, so feel free to ignore me,
> > > > but this seems similar to the code below, could be in one function
> > >
> > > Do you mean get_rel_offset()? That one is for data symbols (USDT
> > > semaphores), so it a) doesn't do arch-specific adjustments and b)
> > > doesn't filter by executable flag. So while the logic of parsing and
> > > finding VMA is similar, conditions and adjustments are different. It
> > > feels not worth combining them, tbh.
> > >
> > > >
> > > > anyway it's good for follow up
> > > >
> > > > there was another selftest in the original patchset adding benchmark
> > > > for the procfs query interface, is it coming in as well?
> > >
> > > I didn't plan to send it, given it's not really a test. But I can put
> > > it on Github somewhere, probably, if it's useful.
> >
> > With and without this selftest applied I see:
> > ./test_progs -t uprobe
> > #416     uprobe:OK
> > #417     uprobe_autoattach:OK
> > [   47.448908] ref_ctr_offset mismatch. inode: 0x16b5f921 offset:
> > 0x2d4297 ref_ctr_offset(old): 0x45e8b56 ref_ctr_offset(new): 0x45e8b54
> > #418/1   uprobe_multi_test/skel_api:OK
> >
> > Is this a known issue?
> 
> Yeah, that's not due to my changes. It's an old warning in uprobe
> internals, but I think we should remove it, because it can trivially
> be triggered by a user. Which is what Jiri is doing intentionally in
> one of selftests to test uprobe failure handling.
> 
> Jiri, maybe let's get rid of this warning?

fine with me.. or change to pr_debug if that makes sense for anyone,
Oleg, any idea/preference?

jirka

> 
> >
> > Applied anyway.
> 
> Thanks! I just found another auto-archived patch of mine, the one
> adding multi-uprobe benchmarks (see patchworks). Please take a look
> and maybe apply, when you get a chance.