sysdeps/i386/tlsdesc.c - nest-cam/v366/glibc - Git at Google

 /* Manage TLS descriptors.  i386 version.
    Copyright (C) 2005, 2008 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, write to the Free
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */

 #include <link.h>
 #include <ldsodefs.h>
 #include <elf/dynamic-link.h>
 #include <tls.h>
 #include <dl-tlsdesc.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)
 {
   __munmap ((void *) (map)->l_map_start,
 	    (map)->l_map_end - (map)->l_map_start);

 #if SHARED
   if (map->l_mach.tlsdesc_table)
     htab_delete (map->l_mach.tlsdesc_table);
 #endif
 }
	/* Manage TLS descriptors. i386 version.
	Copyright (C) 2005, 2008 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, write to the Free
	Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
	02111-1307 USA. */

	#include <link.h>
	#include <ldsodefs.h>
	#include <elf/dynamic-link.h>
	#include <tls.h>
	#include <dl-tlsdesc.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)
	{
	__munmap ((void *) (map)->l_map_start,
	(map)->l_map_end - (map)->l_map_start);

	#if SHARED
	if (map->l_mach.tlsdesc_table)
	htab_delete (map->l_mach.tlsdesc_table);
	#endif
	}