netdev - Re: [PATCH 1/3] elf_symtab: Add support for SHN_XINDEX index to elf_section_by

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Message-ID: <20210121233405.GA14067@krava>
Date:   Fri, 22 Jan 2021 00:34:05 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>, dwarves@...r.kernel.org,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Yonghong Song <yhs@...com>, Hao Luo <haoluo@...gle.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Mark Wielaard <mjw@...hat.com>
Subject: Re: [PATCH 1/3] elf_symtab: Add support for SHN_XINDEX index to
 elf_section_by_name

On Thu, Jan 21, 2021 at 03:10:25PM -0800, Andrii Nakryiko wrote:
> On Thu, Jan 21, 2021 at 12:24 PM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > In case the elf's header e_shstrndx contains SHN_XINDEX,
> > we need to call elf_getshdrstrndx to get the proper
> > string table index.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  dutil.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/dutil.c b/dutil.c
> > index 7b667647420f..9e0fdca3ae04 100644
> > --- a/dutil.c
> > +++ b/dutil.c
> > @@ -179,13 +179,17 @@ Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
> >  {
> >         Elf_Scn *sec = NULL;
> >         size_t cnt = 1;
> > +       size_t str_idx;
> > +
> > +       if (elf_getshdrstrndx(elf, &str_idx))
> > +               return NULL;
> >
> >         while ((sec = elf_nextscn(elf, sec)) != NULL) {
> >                 char *str;
> >
> >                 gelf_getshdr(sec, shp);
> > -               str = elf_strptr(elf, ep->e_shstrndx, shp->sh_name);
> > -               if (!strcmp(name, str)) {
> > +               str = elf_strptr(elf, str_idx, shp->sh_name);
> > +               if (str && !strcmp(name, str)) {
> 
> if (!str) would be an error? should we bail out here?

seems like if elf_nextscn returns NULL, it will be the case for all the
sections in here.. but bailing out on (!str) is more direct and safer

I'll send an update

thanks,
jirka

> 
> >                         if (index)
> >                                 *index = cnt;
> >                         break;
> > --
> > 2.27.0
> >
>