Re: [PATCH 1/2] elf_symtab: Add support for SHN_XINDEX index to elf_section_by_name
From: Arnaldo Carvalho de Melo <acme@kernel.org>
Date: 2021-01-22 22:39:55
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netdev
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
quoted hunk ↗ jump to hunk
Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- 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