Re: Build failures: unresolved symbol vfs_getattr

[Jiri Olsa <jolsa@redhat.com>]

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

> 
> >
> > 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

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);
> 
> [...]
>