On Tue, Jan 19, 2021 at 2:15 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> For very large ELF objects (with many sections), we could
> get special value SHN_XINDEX (65535) for elf object's string
> table index - e_shstrndx.
>
> In such case we need to call elf_getshdrstrndx to get the
> proper string table index.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> tools/lib/bpf/btf.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 3c3f2bc6c652..4fe987846bc0 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -863,6 +863,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
> Elf_Scn *scn = NULL;
> Elf *elf = NULL;
> GElf_Ehdr ehdr;
> + size_t shstrndx;
>
> if (elf_version(EV_CURRENT) == EV_NONE) {
> pr_warn("failed to init libelf for %s\n", path);
> @@ -887,7 +888,16 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
> pr_warn("failed to get EHDR from %s\n", path);
> goto done;
> }
> - if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {
> +
> + /*
> + * Get string table index from extended section index
> + * table if needed.
> + */
> + shstrndx = ehdr.e_shstrndx;
> + if (shstrndx == SHN_XINDEX && elf_getshdrstrndx(elf, &shstrndx))
> + goto done;
just use elf_getshdrstrndx() unconditionally, it works for extended
and non-extended numbering (see libbpf.c).
> +
> + if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
> pr_warn("failed to get e_shstrndx from %s\n", path);
> goto done;
> }
> @@ -902,7 +912,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
> idx, path);
> goto done;
> }
> - name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name);
> + name = elf_strptr(elf, shstrndx, sh.sh_name);
> if (!name) {
> pr_warn("failed to get section(%d) name from %s\n",
> idx, path);
> --
> 2.27.0
>
