1/* Hash table for TLS descriptors.
2 Copyright (C) 2005-2017 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Alexandre Oliva <aoliva@redhat.com>
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <http://www.gnu.org/licenses/>. */
19
20#ifndef TLSDESCHTAB_H
21# define TLSDESCHTAB_H 1
22
23#include <atomic.h>
24
25# ifdef SHARED
26
27# include <inline-hashtab.h>
28
29inline static int
30hash_tlsdesc (void *p)
31{
32 struct tlsdesc_dynamic_arg *td = p;
33
34 /* We know all entries are for the same module, so ti_offset is the
35 only distinguishing entry. */
36 return td->tlsinfo.ti_offset;
37}
38
39inline static int
40eq_tlsdesc (void *p, void *q)
41{
42 struct tlsdesc_dynamic_arg *tdp = p, *tdq = q;
43
44 return tdp->tlsinfo.ti_offset == tdq->tlsinfo.ti_offset;
45}
46
47inline static size_t
48map_generation (struct link_map *map)
49{
50 size_t idx = map->l_tls_modid;
51 struct dtv_slotinfo_list *listp = GL(dl_tls_dtv_slotinfo_list);
52
53 /* Find the place in the dtv slotinfo list. */
54 do
55 {
56 /* Does it fit in the array of this list element? */
57 if (idx < listp->len)
58 {
59 /* We should never get here for a module in static TLS, so
60 we can assume that, if the generation count is zero, we
61 still haven't determined the generation count for this
62 module. */
63 if (listp->slotinfo[idx].map == map && listp->slotinfo[idx].gen)
64 return listp->slotinfo[idx].gen;
65 else
66 break;
67 }
68 idx -= listp->len;
69 listp = listp->next;
70 }
71 while (listp != NULL);
72
73 /* If we get to this point, the module still hasn't been assigned an
74 entry in the dtv slotinfo data structures, and it will when we're
75 done with relocations. At that point, the module will get a
76 generation number that is one past the current generation, so
77 return exactly that. */
78 return GL(dl_tls_generation) + 1;
79}
80
81void *
82internal_function
83_dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset)
84{
85 struct hashtab *ht;
86 void **entry;
87 struct tlsdesc_dynamic_arg *td, test;
88
89 /* FIXME: We could use a per-map lock here, but is it worth it? */
90 __rtld_lock_lock_recursive (GL(dl_load_lock));
91
92 ht = map->l_mach.tlsdesc_table;
93 if (! ht)
94 {
95 ht = htab_create ();
96 if (! ht)
97 {
98 __rtld_lock_unlock_recursive (GL(dl_load_lock));
99 return 0;
100 }
101 map->l_mach.tlsdesc_table = ht;
102 }
103
104 test.tlsinfo.ti_module = map->l_tls_modid;
105 test.tlsinfo.ti_offset = ti_offset;
106 entry = htab_find_slot (ht, &test, 1, hash_tlsdesc, eq_tlsdesc);
107 if (! entry)
108 {
109 __rtld_lock_unlock_recursive (GL(dl_load_lock));
110 return 0;
111 }
112
113 if (*entry)
114 {
115 td = *entry;
116 __rtld_lock_unlock_recursive (GL(dl_load_lock));
117 return td;
118 }
119
120 *entry = td = malloc (sizeof (struct tlsdesc_dynamic_arg));
121 /* This may be higher than the map's generation, but it doesn't
122 matter much. Worst case, we'll have one extra DTV update per
123 thread. */
124 td->gen_count = map_generation (map);
125 td->tlsinfo = test.tlsinfo;
126
127 __rtld_lock_unlock_recursive (GL(dl_load_lock));
128 return td;
129}
130
131# endif /* SHARED */
132
133/* The idea of the following two functions is to stop multiple threads
134 from attempting to resolve the same TLS descriptor without busy
135 waiting. Ideally, we should be able to release the lock right
136 after changing td->entry, and then using say a condition variable
137 or a futex wake to wake up any waiting threads, but let's try to
138 avoid introducing such dependencies. */
139
140static int
141_dl_tlsdesc_resolve_early_return_p (struct tlsdesc volatile *td, void *caller)
142{
143 if (caller != atomic_load_relaxed (&td->entry))
144 return 1;
145
146 __rtld_lock_lock_recursive (GL(dl_load_lock));
147 if (caller != atomic_load_relaxed (&td->entry))
148 {
149 __rtld_lock_unlock_recursive (GL(dl_load_lock));
150 return 1;
151 }
152
153 atomic_store_relaxed (&td->entry, _dl_tlsdesc_resolve_hold);
154
155 return 0;
156}
157
158static void
159_dl_tlsdesc_wake_up_held_fixups (void)
160{
161 __rtld_lock_unlock_recursive (GL(dl_load_lock));
162}
163
164#endif
165