| Message ID | 20210122163920.59177-2-jolsa@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | libbpf: Add support to use optional extended section index table | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
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@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 >
On Fri, Jan 22, 2021 at 9:22 AM Jiri Olsa <jolsa@kernel.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@kernel.org> > --- Acked-by: Andrii Nakryiko <andrii@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 >
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;
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@kernel.org> --- dutil.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)