Re: [Elftoolchain-developers] Problem with elf_update after elf_flagshdr

[Joseph K. <jk...@us...>]

> I am going through all sections with elf_nextscn() then getting the
> header with elf32_getshdr(). For some sections I modify the sh_flags
> member of the shdr, and then call elf_flagshdr on the scn.

> When I call elf_update, though, the sh_size member of shdrs whose
> flags I updated is set to zero!

> Using gdb and a watchpoint, I found that the sh_size member is being
> zeroed in _libelf_compute_section_extents(). I think the problem is
> when _libelf_compute_section_extents sees a scn marked dirty, it
> recomputes its size by adding up the Elf_Data d_size
> values. However, because I haven't used elf_getdata on the scn, the
> scn's s->s_data STAILQ is empty, and so the scn_size remains at
> zero. This is backed up by that fact that if I do elf_getdata on the
> scn before doing elf_flagshdr, the problem goes away. I also note
> that the problem does not happen with the LGPL version of libelf.

> I believe the solution would be to ensure that the Elf_Data
> structures are loaded before calculating the section size in
> _libelf_compute_section_extents().

I'll look into this.  It would *really* help if you could send over a
short program that demonstrates the problem.

Thanks,
Koshy