Re: Build failures: unresolved symbol vfs_getattr

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Oct 23, 2020 at 1:45 PM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Fri, Oct 23, 2020 at 01:32:44PM -0700, Andrii Nakryiko wrote:
>
> SNIP
>
> > > right, we can generate them in bpftrace, but it's a shame
> > >
> > >
> > > >
> > > > But otherwise, I don't really have a good feeling what's the perfect
> > > > solution here...
> > >
> > > I tried the check of dwarf record against function symbols
> > > with adresses mentioned earlier (attached)
> > >
> > > getting more functions of course ;-)
> > >
> > > $ bpftool btf dump file ./vmlinux | grep 'FUNC '  | wc -l
> > > 46606
> > >
> > > compared to 22869 on the same .config with working gcc
> > > and current pahole
> >
> > Just curious, what's the change in BTF size due to this?
>
> current: 3342279
> new:     4361045
>
> so about 1MB

ok, not too bad for almost 24k functions and bringing fentry/fexit on
par with kprobe/kretprobe in terms of what to attach to

>
> >
> > >
> > > and resolve_btfids is happy, because there are no duplications
> > >
> > > jirka
> > >
> > >
> > > ---
> >
> > [...]
> >
> > >  static int btf_var_secinfo_cmp(const void *a, const void *b)
> > >  {
> > >         const struct btf_var_secinfo *av = a;
> > > @@ -72,6 +157,7 @@ struct btf_elf *btf_elf__new(const char *filename, Elf *elf)
> > >         if (!btfe)
> > >                 return NULL;
> > >
> > > +       btfe->symbols = RB_ROOT;
> >
> > Can you please check what we do for per-cpu variables with ELF
> > symbols? Perhaps we can unify approaches. I'd also favor using a sort
> > + bsearch approach instead of rb_tree, given we don't really need to
> > dynamically add/delete elements, it's a one-time operation to iterate
> > and initialize everything. Also binary search of linear arrays would
> > be more memory-efficient and cache-efficient, most probably.
>
> ok, will check
>

thanks!

> jirka
>
> >
> > >         btfe->in_fd = -1;
> > >         btfe->filename = strdup(filename);
> > >         if (btfe->filename == NULL)
> > > @@ -177,6 +263,7 @@ void btf_elf__delete(struct btf_elf *btfe)
> > >                         elf_end(btfe->elf);
> > >         }
> > >
> > > +       btfe__delete_symbols(btfe);
> > >         elf_symtab__delete(btfe->symtab);
> > >         __gobuffer__delete(&btfe->percpu_secinfo);
> > >         btf__free(btfe->btf);
> >
> > [...]
> >
>