Re: [PATCH 3/3] csu: Move static pie self relocation later [BZ #27072]

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 01/07/2021 13:03, H.J. Lu wrote:
> On Thu, Jan 7, 2021 at 3:04 AM Szabolcs Nagy via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >  #ifndef SHARED
> > +# ifndef PI_STATIC_AND_HIDDEN
> > +  /* Do static pie self relocation as early as possible.  */
> >    _dl_relocate_static_pie ();
> > +# endif
> 
> It should be simply removed. PI_STATIC_AND_HIDDEN should be
> required for static PIE.

i guess that makes sense, i can add an assertion for that.

> >    char **ev = &argv[argc + 1];
> >
> > @@ -191,6 +194,13 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
> 
> Does
>    {
>       /* Starting from binutils-2.23, the linker will define the
>          magic symbol __ehdr_start to point to our own ELF header
>          if it is visible in a segment that also includes the phdrs.
>          So we can set up _dl_phdr and _dl_phnum even without any
>          information from auxv.  */
> 
>       extern const ElfW(Ehdr) __ehdr_start
>         __attribute__ ((weak, visibility ("hidden")));
>       if (&__ehdr_start != NULL)
>         {
>           assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
>           GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
>           GL(dl_phnum) = __ehdr_start.e_phnum;
>         }
>     }
> 
> here require RELATIVE relocation?

hm indeed __ehdr_start is accessed via GOT.
(i thought pc relative access would work, but
i guess that cannot work for an undefined
weak symbol.)

without relocation processing &__ehdr_start
will always evaluate to 0, i.e. as if it was
undefined.

but i think GL(dl_phdr) is only used much
later so it can be moved after self relocs.
that would also make it clear that we don't
use anything here from phdrs that might
require relocations.

i'll fix this.