Em Fri, Jan 22, 2021 at 05:39:19PM +0100, Jiri Olsa escreveu:
> In case the elf's header e_shstrndx contains SHN_XINDEX,
> we need to call elf_getshdrstrndx to get the proper
> string table index.
Applied, but changed the changelog comment to:
------------------------------------------------------------------
elf_symtab: Handle SHN_XINDEX index in elf_section_by_name()
Use elf_getshdrstrndx() to cover the case where the ELF header
'e_shstrndx' field contains the special value SHN_XINDEX so that we get
the proper string table index.
This is necessary to handle files with over 65536 sections, such as when
building the kernel with -f[function|data]-sections. Other cases may
include when using FG-ASLR, LTO.
With so many sections, ELF is using extended section index table, which
is used to hold values for some of the indexes and extra code is needed
to retrieve them.
------------------------------------------------------------------
This is from the thread, so that we can have a more comprehensive idea
of what is this SHN_XINDEX and where it can show up when looking at this
code 10 years from now (or next month) :-)
Holler if I've messed up something.
Thanks,
- Arnaldo
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> dutil.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/dutil.c b/dutil.c
> index 7b667647420f..11fb7202049c 100644
> --- a/dutil.c
> +++ b/dutil.c
> @@ -179,12 +179,18 @@ 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);
> + str = elf_strptr(elf, str_idx, shp->sh_name);
> + if (!str)
> + return NULL;
> if (!strcmp(name, str)) {
> if (index)
> *index = cnt;
> --
> 2.26.2
>
--
- Arnaldo
