Re: [PATCH 2/3] bpf_encoder: Translate SHN_XINDEX in symbol's st_shndx values

On Sat, Jan 23, 2021 at 09:08:15PM +0100, Mark Wielaard wrote:

Hi Jiri,

On Sat, 2021-01-23 at 19:51 +0100, Jiri Olsa wrote:

quoted

On Fri, Jan 22, 2021 at 02:55:51PM -0800, Andrii Nakryiko wrote:

quoted

quoted

I don't understand this..  gelf_getsymshndx will return both
symbol and proper index, no? also sym_sec_idx is already
assigned from previou call

Reading (some) implementation of gelf_getsymshndx() that I found
online, it won't set sym_sec_idx, if the symbol *doesn't* use
extended
numbering. But it will still return symbol data. So to return the

the latest upstream code seems to set it always,
but I agree we should be careful

Mark, any insight in here? thanks

GElf_Sym *
gelf_getsymshndx (Elf_Data *symdata, Elf_Data *shndxdata, int ndx,
                  GElf_Sym *dst, Elf32_Word *dstshndx)

Will always set *dst, but only set *dstshndx if both it and shndxdata
are not NULL and no error occurred (the function returns NULL and set
libelf_error in case of error).

So as long as shndxdata != NULL you can rely on *dstshndx being set.
Otherwise you get the section index from dst->st_shndx.

ok, so it's as Andrii said, I'll make the extra check then

thanks,
jirka