glibc/sysdeps/arm/tlsdesc.c

/* Manage TLS descriptors.  ARM version.
   Copyright (C) 2005-2017 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library.  If not, see
   <http://www.gnu.org/licenses/>.  */

#include <link.h>
#include <ldsodefs.h>
#include <elf/dynamic-link.h>
#include <tls.h>
#include <dl-tlsdesc.h>
#include <dl-unmap-segments.h>
#include <tlsdeschtab.h>

/* This function is used to lazily resolve TLS_DESC REL relocations
   Besides the TLS descriptor itself, we get the module's got address
   as the second parameter. */

void
attribute_hidden
_dl_tlsdesc_lazy_resolver_fixup (struct tlsdesc volatile *td,
				 Elf32_Addr *got)
{
  struct link_map *l = (struct link_map *)got[1];
  lookup_t result;
  unsigned long value;

  if (_dl_tlsdesc_resolve_early_return_p
      (td, (void*)(D_PTR (l, l_info[ADDRIDX (DT_TLSDESC_PLT)]) + l->l_addr)))
    return;

  if (td->argument.value & 0x80000000)
    {
      /* A global symbol, this is the symbol index.  */
      /* The code below was borrowed from _dl_fixup().  */
      const Elf_Symndx symndx = td->argument.value ^ 0x80000000;
      const ElfW(Sym) *const symtab
	= (const void *) D_PTR (l, l_info[DT_SYMTAB]);
      const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
      const ElfW(Sym) *sym = &symtab[symndx];

      /* Look up the target symbol.  If the normal lookup rules are not
	 used don't look in the global scope.  */
      if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
	  && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
	{
	  const struct r_found_version *version = NULL;

	  if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
	    {
	      const ElfW(Half) *vernum =
		(const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
	      ElfW(Half) ndx = vernum[symndx] & 0x7fff;
	      version = &l->l_versions[ndx];
	      if (version->hash == 0)
		version = NULL;
	    }

	  result = _dl_lookup_symbol_x
	    (strtab + sym->st_name, l, &sym,
	     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
	     DL_LOOKUP_ADD_DEPENDENCY, NULL);
	  if (sym)
	    value = sym->st_value;
	  else
	    {
	      td->entry = _dl_tlsdesc_undefweak;
	      goto done;
	    }
	}
      else
	{
	  /* We already found the symbol.  The module (and therefore its load
	     address) is also known.  */
	  result = l;
	  value = sym->st_value;
	}
    }
  else
    {
      /* A local symbol, this is the offset within our tls section.
	 */
      value = td->argument.value;
      result = l;
    }

#ifndef SHARED
  CHECK_STATIC_TLS (l, result);
#else
  if (!TRY_STATIC_TLS (l, result))
    {
      td->argument.pointer = _dl_make_tlsdesc_dynamic (result, value);
      td->entry = _dl_tlsdesc_dynamic;
    }
  else
#endif
    {
      td->argument.value = value + result->l_tls_offset;
      td->entry = _dl_tlsdesc_return;
    }

 done:
  _dl_tlsdesc_wake_up_held_fixups ();
}

/* This function is used to avoid busy waiting for other threads to
   complete the lazy relocation.  Once another thread wins the race to
   relocate a TLS descriptor, it sets the descriptor up such that this
   function is called to wait until the resolver releases the
   lock.  */

void
attribute_hidden
_dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
				void *caller)
{
  /* Maybe we're lucky and can return early.  */
  if (caller != td->entry)
    return;

  /* Locking here will stop execution until the running resolver runs
     _dl_tlsdesc_wake_up_held_fixups(), releasing the lock.

     FIXME: We'd be better off waiting on a condition variable, such
     that we didn't have to hold the lock throughout the relocation
     processing.  */
  __rtld_lock_lock_recursive (GL(dl_load_lock));
  __rtld_lock_unlock_recursive (GL(dl_load_lock));
}

/* Unmap the dynamic object, but also release its TLS descriptor table
   if there is one.  */

void
internal_function
_dl_unmap (struct link_map *map)
{
  _dl_unmap_segments (map);

#ifdef SHARED
  /* _dl_unmap is only called for dlopen()ed libraries, for which
     calling free() is safe, or before we've completed the initial
     relocation, in which case calling free() is probably pointless,
     but still safe.  */
  if (map->l_mach.tlsdesc_table)
    htab_delete (map->l_mach.tlsdesc_table);
#endif
}