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

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Date:   Tue, 19 Jan 2021 17:23:00 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     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 Tue, Jan 19, 2021 at 2:16 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..321f4be6669e 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 shstrndx = ep->e_shstrndx;
> +
> +       if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx))
> +               return NULL;
>

see comment for patch #3, no need for SHN_XINDEX checks,
elf_getshdrstrndx() handles this transparently

>         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, shstrndx, shp->sh_name);
> +               if (str && !strcmp(name, str)) {
>                         if (index)
>                                 *index = cnt;
>                         break;
> --
> 2.27.0
>