[thirdparty/glibc.git] / sysdeps / i386 / tlsdesc.c

/* Manage TLS descriptors.  i386 version.
   Copyright (C) 2005-2015 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>

/* The following 4 functions take an entry_check_offset argument.
   It's computed by the caller as an offset between its entry point
   and the call site, such that by adding the built-in return address
   that is implicitly passed to the function with this offset, we can
   easily obtain the caller's entry point to compare with the entry
   point given in the TLS descriptor.  If it's changed, we want to
   return immediately.  */

/* This function is used to lazily resolve TLS_DESC REL relocations
   that reference the *ABS* segment in their own link maps.  The
   argument is the addend originally stored there.  */

void
__attribute__ ((regparm (3))) attribute_hidden
_dl_tlsdesc_resolve_abs_plus_addend_fixup (struct tlsdesc volatile *td,
					   struct link_map *l,
					   ptrdiff_t entry_check_offset)
{
  ptrdiff_t addend = (ptrdiff_t) td->arg;

  if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
					  - entry_check_offset))
    return;

#ifndef SHARED
  CHECK_STATIC_TLS (l, l);
#else
  if (!TRY_STATIC_TLS (l, l))
    {
      td->arg = _dl_make_tlsdesc_dynamic (l, addend);
      td->entry = _dl_tlsdesc_dynamic;
    }
  else
#endif
    {
      td->arg = (void*) (addend - l->l_tls_offset);
      td->entry = _dl_tlsdesc_return;
    }

  _dl_tlsdesc_wake_up_held_fixups ();
}

/* This function is used to lazily resolve TLS_DESC REL relocations
   that originally had zero addends.  The argument location, that
   originally held the addend, is used to hold a pointer to the
   relocation, but it has to be restored before we call the function
   that applies relocations.  */

void
__attribute__ ((regparm (3))) attribute_hidden
_dl_tlsdesc_resolve_rel_fixup (struct tlsdesc volatile *td,
			       struct link_map *l,
			       ptrdiff_t entry_check_offset)
{
  const ElfW(Rel) *reloc = td->arg;

  if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
					  - entry_check_offset))
    return;

  /* The code below was borrowed from _dl_fixup(),
     except for checking for STB_LOCAL.  */
  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 = 0;
      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);
	  td->entry = _dl_tlsdesc_dynamic;
	}
      else
#  endif
	{
	  td->arg = (void*)(sym->st_value - result->l_tls_offset);
	  td->entry = _dl_tlsdesc_return;
	}
    }

  _dl_tlsdesc_wake_up_held_fixups ();
}

/* 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__ ((regparm (3))) attribute_hidden
_dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
				struct link_map *l,
				ptrdiff_t entry_check_offset)
{
  const ElfW(Rela) *reloc = td->arg;

  if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
					  - entry_check_offset))
    return;

  /* The code below was borrowed from _dl_fixup(),
     except for checking for STB_LOCAL.  */
  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__ ((regparm (3))) attribute_hidden
_dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
				struct link_map *l __attribute__((__unused__)),
				ptrdiff_t entry_check_offset)
{
  /* Maybe we're lucky and can return early.  */
  if (__builtin_return_address (0) - entry_check_offset != 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
  if (map->l_mach.tlsdesc_table)
    htab_delete (map->l_mach.tlsdesc_table);
#endif
}
Commit	Line	Data
c9ff0187	1	/* Manage TLS descriptors. i386 version.
b168057a	2	Copyright (C) 2005-2015 Free Software Foundation, Inc.
c9ff0187 UD	3	This file is part of the GNU C Library.
	4
	5	The GNU C Library is free software; you can redistribute it and/or
	6	modify it under the terms of the GNU Lesser General Public
	7	License as published by the Free Software Foundation; either
	8	version 2.1 of the License, or (at your option) any later version.
	9
	10	The GNU C Library is distributed in the hope that it will be useful,
	11	but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	13	Lesser General Public License for more details.
	14
	15	You should have received a copy of the GNU Lesser General Public
59ba27a6 PE	16	License along with the GNU C Library; if not, see
59ba27a6 PE	17	<http://www.gnu.org/licenses/>. */
c9ff0187 UD	18
	19	#include <link.h>
	20	#include <ldsodefs.h>
	21	#include <elf/dynamic-link.h>
	22	#include <tls.h>
	23	#include <dl-tlsdesc.h>
fcccd512	24	#include <dl-unmap-segments.h>
c9ff0187 UD	25	#include <tlsdeschtab.h>
	26
	27	/* The following 4 functions take an entry_check_offset argument.
	28	It's computed by the caller as an offset between its entry point
	29	and the call site, such that by adding the built-in return address
	30	that is implicitly passed to the function with this offset, we can
	31	easily obtain the caller's entry point to compare with the entry
	32	point given in the TLS descriptor. If it's changed, we want to
	33	return immediately. */
	34
	35	/* This function is used to lazily resolve TLS_DESC REL relocations
	36	that reference the ABS segment in their own link maps. The
	37	argument is the addend originally stored there. */
	38
	39	void
	40	__attribute__ ((regparm (3))) attribute_hidden
	41	_dl_tlsdesc_resolve_abs_plus_addend_fixup (struct tlsdesc volatile *td,
	42	struct link_map *l,
	43	ptrdiff_t entry_check_offset)
	44	{
	45	ptrdiff_t addend = (ptrdiff_t) td->arg;
	46
	47	if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
	48	- entry_check_offset))
	49	return;
	50
	51	#ifndef SHARED
	52	CHECK_STATIC_TLS (l, l);
	53	#else
	54	if (!TRY_STATIC_TLS (l, l))
	55	{
	56	td->arg = _dl_make_tlsdesc_dynamic (l, addend);
	57	td->entry = _dl_tlsdesc_dynamic;
	58	}
	59	else
	60	#endif
	61	{
	62	td->arg = (void*) (addend - l->l_tls_offset);
	63	td->entry = _dl_tlsdesc_return;
	64	}
	65
	66	_dl_tlsdesc_wake_up_held_fixups ();
	67	}
	68
	69	/* This function is used to lazily resolve TLS_DESC REL relocations
	70	that originally had zero addends. The argument location, that
	71	originally held the addend, is used to hold a pointer to the
	72	relocation, but it has to be restored before we call the function
	73	that applies relocations. */
	74
	75	void
	76	__attribute__ ((regparm (3))) attribute_hidden
	77	_dl_tlsdesc_resolve_rel_fixup (struct tlsdesc volatile *td,
	78	struct link_map *l,
	79	ptrdiff_t entry_check_offset)
	80	{
	81	const ElfW(Rel) *reloc = td->arg;
	82
	83	if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
	84	- entry_check_offset))
	85	return;
	86
	87	/* The code below was borrowed from _dl_fixup(),
	88	except for checking for STB_LOCAL. */
89	const ElfW(Sym) *const symtab
90	= (const void *) D_PTR (l, l_info[DT_SYMTAB]);
91	const char strtab = (const void ) D_PTR (l, l_info[DT_STRTAB]);
92	const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
93	lookup_t result;
94
95	/* Look up the target symbol. If the normal lookup rules are not
96	used don't look in the global scope. */
97	if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
98	&& __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
99	{
100	const struct r_found_version *version = NULL;
101
102	if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
103	{
104	const ElfW(Half) *vernum =
105	(const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
106	ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
107	version = &l->l_versions[ndx];
108	if (version->hash == 0)
109	version = NULL;
110	}
111
112	result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
113	l->l_scope, version, ELF_RTYPE_CLASS_PLT,
114	DL_LOOKUP_ADD_DEPENDENCY, NULL);
115	}
116	else
117	{
118	/* We already found the symbol. The module (and therefore its load
119	address) is also known. */
120	result = l;
121	}
122
123	if (!sym)
124	{
125	td->arg = 0;
126	td->entry = _dl_tlsdesc_undefweak;
127	}
128	else
129	{
130	# ifndef SHARED
131	CHECK_STATIC_TLS (l, result);
132	# else
133	if (!TRY_STATIC_TLS (l, result))
134	{
135	td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value);
136	td->entry = _dl_tlsdesc_dynamic;
137	}
138	else
139	# endif
140	{
141	td->arg = (void*)(sym->st_value - result->l_tls_offset);
142	td->entry = _dl_tlsdesc_return;
143	}
144	}
145
146	_dl_tlsdesc_wake_up_held_fixups ();
147	}
148
149	/* This function is used to lazily resolve TLS_DESC RELA relocations.
150	The argument location is used to hold a pointer to the relocation. */
151
152	void
153	__attribute__ ((regparm (3))) attribute_hidden
154	_dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
155	struct link_map *l,
156	ptrdiff_t entry_check_offset)
157	{
158	const ElfW(Rela) *reloc = td->arg;
159
160	if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
161	- entry_check_offset))
162	return;
163
164	/* The code below was borrowed from _dl_fixup(),
165	except for checking for STB_LOCAL. */
166	const ElfW(Sym) *const symtab
167	= (const void *) D_PTR (l, l_info[DT_SYMTAB]);
168	const char strtab = (const void ) D_PTR (l, l_info[DT_STRTAB]);
169	const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
170	lookup_t result;
171
172	/* Look up the target symbol. If the normal lookup rules are not
173	used don't look in the global scope. */
174	if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
175	&& __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
176	{
177	const struct r_found_version *version = NULL;
178
179	if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
180	{
181	const ElfW(Half) *vernum =
182	(const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
183	ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
184	version = &l->l_versions[ndx];
185	if (version->hash == 0)
186	version = NULL;
187	}
188
189	result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
190	l->l_scope, version, ELF_RTYPE_CLASS_PLT,
191	DL_LOOKUP_ADD_DEPENDENCY, NULL);
192	}
193	else
194	{
195	/* We already found the symbol. The module (and therefore its load
196	address) is also known. */
197	result = l;
198	}
199
200	if (!sym)
201	{
f05ac8f5	202	td->arg = (void*) reloc->r_addend;
c9ff0187 UD	203	td->entry = _dl_tlsdesc_undefweak;
	204	}
	205	else
	206	{
	207	# ifndef SHARED
	208	CHECK_STATIC_TLS (l, result);
	209	# else
	210	if (!TRY_STATIC_TLS (l, result))
	211	{
	212	td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value
	213	+ reloc->r_addend);
	214	td->entry = _dl_tlsdesc_dynamic;
	215	}
	216	else
	217	# endif
	218	{
f05ac8f5 UD	219	td->arg = (void*) (sym->st_value - result->l_tls_offset
f05ac8f5 UD	220	+ reloc->r_addend);
c9ff0187 UD	221	td->entry = _dl_tlsdesc_return;
	222	}
	223	}
	224
	225	_dl_tlsdesc_wake_up_held_fixups ();
	226	}
	227
	228	/* This function is used to avoid busy waiting for other threads to
	229	complete the lazy relocation. Once another thread wins the race to
	230	relocate a TLS descriptor, it sets the descriptor up such that this
	231	function is called to wait until the resolver releases the
	232	lock. */
	233
	234	void
	235	__attribute__ ((regparm (3))) attribute_hidden
	236	_dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
	237	struct link_map *l __attribute__((__unused__)),
	238	ptrdiff_t entry_check_offset)
	239	{
	240	/* Maybe we're lucky and can return early. */
	241	if (__builtin_return_address (0) - entry_check_offset != td->entry)
	242	return;
	243
	244	/* Locking here will stop execution until the running resolver runs
	245	_dl_tlsdesc_wake_up_held_fixups(), releasing the lock.
	246
	247	FIXME: We'd be better off waiting on a condition variable, such
	248	that we didn't have to hold the lock throughout the relocation
	249	processing. */
	250	__rtld_lock_lock_recursive (GL(dl_load_lock));
	251	__rtld_lock_unlock_recursive (GL(dl_load_lock));
	252	}
	253
	254
	255	/* Unmap the dynamic object, but also release its TLS descriptor table
	256	if there is one. */
	257
	258	void
	259	internal_function
	260	_dl_unmap (struct link_map *map)
	261	{
fcccd512	262	_dl_unmap_segments (map);
c9ff0187	263
82374e65	264	#ifdef SHARED
c9ff0187 UD	265	if (map->l_mach.tlsdesc_table)
	266	htab_delete (map->l_mach.tlsdesc_table);
	267	#endif
	268	}