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

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Hi Jiri,

On Sat, 2021-01-23 at 19:51 +0100, Jiri Olsa wrote:
> On Fri, Jan 22, 2021 at 02:55:51PM -0800, Andrii Nakryiko wrote:
> > 
> > > 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.

Cheers,

Mark



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