Re: Update on the glibc segfault issue on Alpha

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella Netto:

> diff --git a/csu/libc-start.c b/csu/libc-start.c
> index 543560f36c..63a3eceaea 100644
> --- a/csu/libc-start.c
> +++ b/csu/libc-start.c
> @@ -271,18 +271,10 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
>           So we can set up _dl_phdr and _dl_phnum even without any
>           information from auxv.  */
>
> -      extern const ElfW(Ehdr) __ehdr_start
> -# if BUILD_PIE_DEFAULT
> -       __attribute__ ((visibility ("hidden")));
> -# else
> -       __attribute__ ((weak, visibility ("hidden")));
> -      if (&__ehdr_start != NULL)
> -# endif
> -        {
> -          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;
> -        }
> +      extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
> +      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;

There's a separate thread that e.ph_off is not actually correct in this
context because it's a file offset that doesn't necessarily match the
virtual memory offset:

  [PATCH 0/1] __libc_start_main() now uses auxv to obtain phdr's address
  [BZ #29864]
  <https://sourceware.org/pipermail/libc-alpha/2022-December/143874.html>

I think this needs to be cleaned up so that the static and dynamic cases
are aligned.  That is, we probably want to do the equivalent of

      GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
      GL(dl_phnum) = __ehdr_start.e_phnum;

in common code.  Ideally, we don't use global variables for that because
in both cases, we only briefly need these variables.

Thanks,
Florian