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TLS data/BSS alignment

Nick Clifton nickc@redhat.com
Mon Mar 23 12:52:33 GMT 2020 
Hi Sebastian,

> Thanks for the hint. I found this code also, but I didn't understand how the different output sections in the ELF file are generated. I guess I have to dig a bit deeper.

Alright, how about this from bfd/elflink.c:

struct bfd_section *
_bfd_elf_tls_setup (bfd *obfd, struct bfd_link_info *info)
{
  struct bfd_section *sec, *tls;
  unsigned int align = 0;

  for (sec = obfd->sections; sec != NULL; sec = sec->next)
    if ((sec->flags & SEC_THREAD_LOCAL) != 0)
      break;
  tls = sec;

  for (; sec != NULL && (sec->flags & SEC_THREAD_LOCAL) != 0; sec = sec->next)
    if (sec->alignment_power > align)
      align = sec->alignment_power;

  elf_hash_table (info)->tls_sec = tls;

  /* Ensure the alignment of the first section is the largest alignment,
     so that the tls segment starts aligned.  */
  if (tls != NULL)
    tls->alignment_power = align;

  return tls;
}

Cheers
  Nick
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