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/* Manage TLS descriptors. x86_64 version.
Copyright (C) 2005-2021 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
<https://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>
/* The following 2 functions take a caller argument, that contains the
address expected to be in the TLS descriptor. If it's changed, we
want to return immediately. */
/* This function is used to lazily resolve TLS_DESC RELA relocations.
The argument location is used to hold a pointer to the relocation. */
void
attribute_hidden
_dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
struct link_map *l)
{
const ElfW(Rela) *reloc = td->arg;
if (_dl_tlsdesc_resolve_early_return_p
(td, (void*)(D_PTR (l, l_info[ADDRIDX (DT_TLSDESC_PLT)]) + l->l_addr)))
return;
/* The code below was borrowed from _dl_fixup(). */
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[ELFW(R_SYM) (reloc->r_info)];
lookup_t result;
/* 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[ELFW(R_SYM) (reloc->r_info)] & 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);
}
else
{
/* We already found the symbol. The module (and therefore its load
address) is also known. */
result = l;
}
if (! sym)
{
td->arg = (void*)reloc->r_addend;
td->entry = _dl_tlsdesc_undefweak;
}
else
{
# ifndef SHARED
CHECK_STATIC_TLS (l, result);
# else
if (!TRY_STATIC_TLS (l, result))
{
td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value
+ reloc->r_addend);
td->entry = _dl_tlsdesc_dynamic;
}
else
# endif
{
td->arg = (void*)(sym->st_value - result->l_tls_offset
+ reloc->r_addend);
td->entry = _dl_tlsdesc_return;
}
}
_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
_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
}
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