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

[Brabes <br...@po...>]

> > 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.

I've uploaded an example to http://brabes.pochta.ru/elf_update_bug.tar.bz2 

Run it the program twice on the some.elf file and note that the sh_size changes as well as the sh_flags. The included log.txt shows my results from running it twice.

Hope that helps :)