1 /* Locate TLS data for a thread.
2 Copyright (C) 2003-2023 Free Software Foundation, Inc.
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
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include "thread_dbP.h"
20 #include <link.h>
21
22 /* Get the DTV slotinfo list head entry from the dynamic loader state
23 into *LISTHEAD. */
24 static td_err_e
25 dtv_slotinfo_list (td_thragent_t *ta,
26 psaddr_t *listhead)
27 {
28 td_err_e err;
29 psaddr_t head;
30
31 if (__td_ta_rtld_global (ta))
32 {
33 err = DB_GET_FIELD (head, ta, ta->ta_addr__rtld_global,
34 rtld_global, _dl_tls_dtv_slotinfo_list, 0);
35 if (err != TD_OK)
36 return err;
37 }
38 else
39 {
40 if (ta->ta_addr__dl_tls_dtv_slotinfo_list == 0
41 && td_mod_lookup (ta->ph, NULL, SYM__dl_tls_dtv_slotinfo_list,
42 &ta->ta_addr__dl_tls_dtv_slotinfo_list) != PS_OK)
43 return TD_ERR;
44
45 err = _td_fetch_value (ta, ta->ta_var__dl_tls_dtv_slotinfo_list,
46 SYM_DESC__dl_tls_dtv_slotinfo_list,
47 0, ta->ta_addr__dl_tls_dtv_slotinfo_list, &head);
48 if (err != TD_OK)
49 return err;
50 }
51
52 *listhead = head;
53 return TD_OK;
54 }
55
56 /* Get the address of the DTV slotinfo entry for MODID into
57 *DTVSLOTINFO. */
58 static td_err_e
59 dtv_slotinfo (td_thragent_t *ta,
60 unsigned long int modid,
61 psaddr_t *dtvslotinfo)
62 {
63 td_err_e err;
64 psaddr_t slot, temp;
65 size_t slbase = 0;
66
67 err = dtv_slotinfo_list (ta, &slot);
68 if (err != TD_OK)
69 return err;
70
71 while (slot)
72 {
73 /* Get the number of entries in this list entry's array. */
74 err = DB_GET_FIELD (temp, ta, slot, dtv_slotinfo_list, len, 0);
75 if (err != TD_OK)
76 return err;
77 size_t len = (uintptr_t)temp;
78
79 /* Did we find the list entry for modid? */
80 if (modid < slbase + len)
81 break;
82
83 /* We didn't, so get the next list entry. */
84 slbase += len;
85 err = DB_GET_FIELD (temp, ta, slot, dtv_slotinfo_list,
86 next, 0);
87 if (err != TD_OK)
88 return err;
89 slot = temp;
90 }
91
92 /* We reached the end of the list and found nothing. */
93 if (!slot)
94 return TD_ERR;
95
96 /* Take the slotinfo for modid from the list entry. */
97 err = DB_GET_FIELD_ADDRESS (temp, ta, slot, dtv_slotinfo_list,
98 slotinfo, modid - slbase);
99 if (err != TD_OK)
100 return err;
101 slot = temp;
102
103 *dtvslotinfo = slot;
104 return TD_OK;
105 }
106
107 /* Return in *BASE the base address of the TLS block for MODID within
108 TH.
109
110 It should return success and yield the correct pointer in any
111 circumstance where the TLS block for the module and thread
112 requested has already been initialized.
113
114 It should fail with TD_TLSDEFER only when the thread could not
115 possibly have observed any values in that TLS block. That way, the
116 debugger can fall back to showing initial values from the PT_TLS
117 segment (and refusing attempts to mutate) for the TD_TLSDEFER case,
118 and never fail to make the values the program will actually see
119 available to the user of the debugger. */
120 td_err_e
121 td_thr_tlsbase (const td_thrhandle_t *th,
122 unsigned long int modid,
123 psaddr_t *base)
124 {
125 td_err_e err;
126 psaddr_t dtv, dtvslot, dtvptr, temp;
127
128 if (modid < 1)
129 return TD_NOTLS;
130
131 psaddr_t pd = th->th_unique;
132 if (pd == 0)
133 {
134 /* This is the fake handle for the main thread before libpthread
135 initialization. We are using 0 for its th_unique because we can't
136 trust that its thread register has been initialized. But we need
137 a real pointer to have any TLS access work. In case of dlopen'd
138 libpthread, initialization might not be for quite some time. So
139 try looking up the thread register now. Worst case, it's nonzero
140 uninitialized garbage and we get bogus results for TLS access
141 attempted too early. Tough. */
142
143 td_thrhandle_t main_th;
144 err = __td_ta_lookup_th_unique (th->th_ta_p, ps_getpid (th->th_ta_p->ph),
145 &main_th);
146 if (err == 0)
147 pd = main_th.th_unique;
148 if (pd == 0)
149 return TD_TLSDEFER;
150 }
151
152 err = dtv_slotinfo (th->th_ta_p, modid, &temp);
153 if (err != TD_OK)
154 return err;
155
156 psaddr_t slot;
157 err = DB_GET_STRUCT (slot, th->th_ta_p, temp, dtv_slotinfo);
158 if (err != TD_OK)
159 return err;
160
161 /* Take the link_map from the slotinfo. */
162 psaddr_t map;
163 err = DB_GET_FIELD_LOCAL (map, th->th_ta_p, slot, dtv_slotinfo, map, 0);
164 if (err != TD_OK)
165 return err;
166 if (!map)
167 return TD_ERR;
168
169 /* Ok, the modid is good, now find out what DTV generation it
170 requires. */
171 err = DB_GET_FIELD_LOCAL (temp, th->th_ta_p, slot, dtv_slotinfo, gen, 0);
172 if (err != TD_OK)
173 return err;
174 size_t modgen = (uintptr_t)temp;
175
176 /* Get the DTV pointer from the thread descriptor. */
177 err = DB_GET_FIELD (dtv, th->th_ta_p, pd, pthread, dtvp, 0);
178 if (err != TD_OK)
179 return err;
180
181 psaddr_t dtvgenloc;
182 /* Get the DTV generation count at dtv[0].counter. */
183 err = DB_GET_FIELD_ADDRESS (dtvgenloc, th->th_ta_p, dtv, dtv, dtv, 0);
184 if (err != TD_OK)
185 return err;
186 err = DB_GET_FIELD (temp, th->th_ta_p, dtvgenloc, dtv_t, counter, 0);
187 if (err != TD_OK)
188 return err;
189 size_t dtvgen = (uintptr_t)temp;
190
191 /* Is the DTV current enough? */
192 if (dtvgen < modgen)
193 {
194 try_static_tls:
195 /* If the module uses Static TLS, we're still good. */
196 err = DB_GET_FIELD (temp, th->th_ta_p, map, link_map, l_tls_offset, 0);
197 if (err != TD_OK)
198 return err;
199 ptrdiff_t tlsoff = (uintptr_t)temp;
200
201 if (tlsoff != FORCED_DYNAMIC_TLS_OFFSET
202 && tlsoff != NO_TLS_OFFSET)
203 {
204 psaddr_t tp = pd;
205
206 #if TLS_TCB_AT_TP
207 dtvptr = tp - tlsoff;
208 #elif TLS_DTV_AT_TP
209 dtvptr = tp + tlsoff + TLS_PRE_TCB_SIZE;
210 #else
211 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
212 #endif
213
214 *base = dtvptr;
215 return TD_OK;
216 }
217
218 return TD_TLSDEFER;
219 }
220
221 /* Find the corresponding entry in the DTV. */
222 err = DB_GET_FIELD_ADDRESS (dtvslot, th->th_ta_p, dtv, dtv, dtv, modid);
223 if (err != TD_OK)
224 return err;
225
226 /* Extract the TLS block address from that DTV slot. */
227 err = DB_GET_FIELD (dtvptr, th->th_ta_p, dtvslot, dtv_t, pointer_val, 0);
228 if (err != TD_OK)
229 return err;
230
231 /* It could be that the memory for this module is not allocated for
232 the given thread. */
233 if ((uintptr_t) dtvptr & 1)
234 goto try_static_tls;
235
236 *base = dtvptr;
237 return TD_OK;
238 }