Re: [PATCH] btf_encoder: Add extra checks for symbol names

[Jiri Olsa <jolsa@redhat.com>]

On Tue, Jan 12, 2021 at 11:20:44AM -0800, Andrii Nakryiko wrote:
> On Tue, Jan 12, 2021 at 10:43 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > When processing kernel image build by clang we can
> > find some functions without the name, which causes
> > pahole to segfault.
> >
> > Adding extra checks to make sure we always have
> > function's name defined before using it.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  btf_encoder.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/btf_encoder.c b/btf_encoder.c
> > index 333973054b61..17f7a14f2ef0 100644
> > --- a/btf_encoder.c
> > +++ b/btf_encoder.c
> > @@ -72,6 +72,8 @@ static int collect_function(struct btf_elf *btfe, GElf_Sym *sym)
> >
> >         if (elf_sym__type(sym) != STT_FUNC)
> >                 return 0;
> > +       if (!elf_sym__name(sym, btfe->symtab))
> > +               return 0;
> 
> elf_sym__name() is called below again, so might be better to just use
> local variable to store result?

right, will add

> 
> >
> >         if (functions_cnt == functions_alloc) {
> >                 functions_alloc = max(1000, functions_alloc * 3 / 2);
> > @@ -730,9 +732,11 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
> >                 if (!has_arg_names(cu, &fn->proto))
> >                         continue;
> >                 if (functions_cnt) {
> > -                       struct elf_function *func;
> > +                       const char *name = function__name(fn, cu);
> > +                       struct elf_function *func = NULL;
> >
> > -                       func = find_function(btfe, function__name(fn, cu));
> > +                       if (name)
> > +                               func = find_function(btfe, name);
> 
> isn't this a more convoluted way of writing:
> 
> name = function__name(fn, cu);
> if (!name)
>     continue;
> 
> func = find_function(btfe, name);
> if (!func || func->generated)
>     continue
> 
> ?

convoluted is my middle name ;-) I'll change it

thanks,
jirka

> 
> >                         if (!func || func->generated)
> >                                 continue;
> >                         func->generated = true;
> > --
> > 2.26.2
> >
>