1 /* Definition for thread-local data handling. nptl/i386 version.
2 Copyright (C) 2002-2023 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 #ifndef _TLS_H
20 #define _TLS_H 1
21
22 #include <dl-sysdep.h>
23 #ifndef __ASSEMBLER__
24 # include <stdbool.h>
25 # include <stddef.h>
26 # include <stdint.h>
27 # include <stdlib.h>
28 # include <sysdep.h>
29 # include <libc-pointer-arith.h> /* For cast_to_integer. */
30 # include <kernel-features.h>
31 # include <dl-dtv.h>
32
33 typedef struct
34 {
35 void *tcb; /* Pointer to the TCB. Not necessarily the
36 thread descriptor used by libpthread. */
37 dtv_t *dtv;
38 void *self; /* Pointer to the thread descriptor. */
39 int multiple_threads;
40 uintptr_t sysinfo;
41 uintptr_t stack_guard;
42 uintptr_t pointer_guard;
43 int gscope_flag;
44 /* Bit 0: X86_FEATURE_1_IBT.
45 Bit 1: X86_FEATURE_1_SHSTK.
46 */
47 unsigned int feature_1;
48 /* Reservation of some values for the TM ABI. */
49 void *__private_tm[3];
50 /* GCC split stack support. */
51 void *__private_ss;
52 /* The lowest address of shadow stack, */
53 unsigned long ssp_base;
54 } tcbhead_t;
55
56 /* morestack.S in libgcc uses offset 0x30 to access __private_ss, */
57 _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x30,
58 "offset of __private_ss != 0x30");
59
60 # define TLS_MULTIPLE_THREADS_IN_TCB 1
61
62 #else /* __ASSEMBLER__ */
63 # include <tcb-offsets.h>
64 #endif
65
66
67 /* Alignment requirement for the stack. For IA-32 this is governed by
68 the SSE memory functions. */
69 #define STACK_ALIGN 16
70
71 #ifndef __ASSEMBLER__
72 /* Get system call information. */
73 # include <sysdep.h>
74
75 /* The old way: using LDT. */
76
77 /* Structure passed to `modify_ldt', 'set_thread_area', and 'clone' calls. */
78 struct user_desc
79 {
80 unsigned int entry_number;
81 unsigned long int base_addr;
82 unsigned int limit;
83 unsigned int seg_32bit:1;
84 unsigned int contents:2;
85 unsigned int read_exec_only:1;
86 unsigned int limit_in_pages:1;
87 unsigned int seg_not_present:1;
88 unsigned int useable:1;
89 unsigned int empty:25;
90 };
91
92 /* Initializing bit fields is slow. We speed it up by using a union. */
93 union user_desc_init
94 {
95 struct user_desc desc;
96 unsigned int vals[4];
97 };
98
99
100 /* This is the size of the initial TCB. Can't be just sizeof (tcbhead_t),
101 because NPTL getpid, __libc_alloca_cutoff etc. need (almost) the whole
102 struct pthread even when not linked with -lpthread. */
103 # define TLS_INIT_TCB_SIZE sizeof (struct pthread)
104
105 /* This is the size of the TCB. */
106 # define TLS_TCB_SIZE sizeof (struct pthread)
107
108 /* The TCB can have any size and the memory following the address the
109 thread pointer points to is unspecified. Allocate the TCB there. */
110 # define TLS_TCB_AT_TP 1
111 # define TLS_DTV_AT_TP 0
112
113 /* Get the thread descriptor definition. */
114 # include <nptl/descr.h>
115
116
117 /* Install the dtv pointer. The pointer passed is to the element with
118 index -1 which contain the length. */
119 # define INSTALL_DTV(descr, dtvp) \
120 ((tcbhead_t *) (descr))->dtv = (dtvp) + 1
121
122 /* Install new dtv for current thread. */
123 # define INSTALL_NEW_DTV(dtvp) \
124 ({ struct pthread *__pd; \
125 THREAD_SETMEM (__pd, header.dtv, (dtvp)); })
126
127 /* Return dtv of given thread descriptor. */
128 # define GET_DTV(descr) \
129 (((tcbhead_t *) (descr))->dtv)
130
131 /* Macros to load from and store into segment registers. */
132 # ifndef TLS_GET_GS
133 # define TLS_GET_GS() \
134 ({ int __seg; __asm ("movw %%gs, %w0" : "=q" (__seg)); __seg & 0xffff; })
135 # endif
136 # ifndef TLS_SET_GS
137 # define TLS_SET_GS(val) \
138 __asm ("movw %w0, %%gs" :: "q" (val))
139 # endif
140
141 #ifdef NEED_DL_SYSINFO
142 # define INIT_SYSINFO \
143 _head->sysinfo = GLRO(dl_sysinfo)
144 # define SETUP_THREAD_SYSINFO(pd) \
145 ((pd)->header.sysinfo = THREAD_GETMEM (THREAD_SELF, header.sysinfo))
146 # define CHECK_THREAD_SYSINFO(pd) \
147 assert ((pd)->header.sysinfo == THREAD_GETMEM (THREAD_SELF, header.sysinfo))
148 #else
149 # define INIT_SYSINFO
150 #endif
151
152 #define LOCK_PREFIX "lock;"
153
154 static inline void __attribute__ ((unused, always_inline))
155 tls_fill_user_desc (union user_desc_init *desc,
156 unsigned int entry_number,
157 void *pd)
158 {
159 desc->vals[0] = entry_number;
160 /* The 'base_addr' field. Pointer to the TCB. */
161 desc->vals[1] = (unsigned long int) pd;
162 /* The 'limit' field. We use 4GB which is 0xfffff pages. */
163 desc->vals[2] = 0xfffff;
164 /* Collapsed value of the bitfield:
165 .seg_32bit = 1
166 .contents = 0
167 .read_exec_only = 0
168 .limit_in_pages = 1
169 .seg_not_present = 0
170 .useable = 1 */
171 desc->vals[3] = 0x51;
172 }
173
174 /* Code to initially initialize the thread pointer. This might need
175 special attention since 'errno' is not yet available and if the
176 operation can cause a failure 'errno' must not be touched. */
177 # define TLS_INIT_TP(thrdescr) \
178 ({ void *_thrdescr = (thrdescr); \
179 tcbhead_t *_head = _thrdescr; \
180 union user_desc_init _segdescr; \
181 int _result; \
182 \
183 _head->tcb = _thrdescr; \
184 /* For now the thread descriptor is at the same address. */ \
185 _head->self = _thrdescr; \
186 /* New syscall handling support. */ \
187 INIT_SYSINFO; \
188 \
189 /* Let the kernel pick a value for the 'entry_number' field. */ \
190 tls_fill_user_desc (&_segdescr, -1, _thrdescr); \
191 \
192 /* Install the TLS. */ \
193 _result = INTERNAL_SYSCALL_CALL (set_thread_area, &_segdescr.desc); \
194 \
195 if (_result == 0) \
196 /* We know the index in the GDT, now load the segment register. \
197 The use of the GDT is described by the value 3 in the lower \
198 three bits of the segment descriptor value. \
199 \
200 Note that we have to do this even if the numeric value of \
201 the descriptor does not change. Loading the segment register \
202 causes the segment information from the GDT to be loaded \
203 which is necessary since we have changed it. */ \
204 TLS_SET_GS (_segdescr.desc.entry_number * 8 + 3); \
205 \
206 _result == 0; })
207
208 # define TLS_DEFINE_INIT_TP(tp, pd) \
209 union user_desc_init _segdescr; \
210 /* Find the 'entry_number' field that the kernel selected in TLS_INIT_TP. \
211 The first three bits of the segment register value select the GDT, \
212 ignore them. We get the index from the value of the %gs register in \
213 the current thread. */ \
214 tls_fill_user_desc (&_segdescr, TLS_GET_GS () >> 3, pd); \
215 const struct user_desc *tp = &_segdescr.desc
216
217
218 /* Return the address of the dtv for the current thread. */
219 # define THREAD_DTV() \
220 ({ struct pthread *__pd; \
221 THREAD_GETMEM (__pd, header.dtv); })
222
223
224 /* Return the thread descriptor for the current thread.
225
226 The contained asm must *not* be marked volatile since otherwise
227 assignments like
228 pthread_descr self = thread_self();
229 do not get optimized away. */
230 # if __GNUC_PREREQ (6, 0)
231 # define THREAD_SELF \
232 (*(struct pthread *__seg_gs *) offsetof (struct pthread, header.self))
233 # else
234 # define THREAD_SELF \
235 ({ struct pthread *__self; \
236 asm ("movl %%gs:%c1,%0" : "=r" (__self) \
237 : "i" (offsetof (struct pthread, header.self))); \
238 __self;})
239 # endif
240
241 /* Magic for libthread_db to know how to do THREAD_SELF. */
242 # define DB_THREAD_SELF \
243 REGISTER_THREAD_AREA (32, offsetof (struct user_regs_struct, xgs), 3) \
244 REGISTER_THREAD_AREA (64, 26 * 8, 3) /* x86-64's user_regs_struct->gs */
245
246 # include <tcb-access.h>
247
248 /* Set the stack guard field in TCB head. */
249 #define THREAD_SET_STACK_GUARD(value) \
250 THREAD_SETMEM (THREAD_SELF, header.stack_guard, value)
251 #define THREAD_COPY_STACK_GUARD(descr) \
252 ((descr)->header.stack_guard \
253 = THREAD_GETMEM (THREAD_SELF, header.stack_guard))
254
255
256 /* Set the pointer guard field in the TCB head. */
257 #define THREAD_SET_POINTER_GUARD(value) \
258 THREAD_SETMEM (THREAD_SELF, header.pointer_guard, value)
259 #define THREAD_COPY_POINTER_GUARD(descr) \
260 ((descr)->header.pointer_guard \
261 = THREAD_GETMEM (THREAD_SELF, header.pointer_guard))
262
263
264 /* Get and set the global scope generation counter in the TCB head. */
265 #define THREAD_GSCOPE_FLAG_UNUSED 0
266 #define THREAD_GSCOPE_FLAG_USED 1
267 #define THREAD_GSCOPE_FLAG_WAIT 2
268 #define THREAD_GSCOPE_RESET_FLAG() \
269 do \
270 { int __res; \
271 asm volatile ("xchgl %0, %%gs:%P1" \
272 : "=r" (__res) \
273 : "i" (offsetof (struct pthread, header.gscope_flag)), \
274 "0" (THREAD_GSCOPE_FLAG_UNUSED)); \
275 if (__res == THREAD_GSCOPE_FLAG_WAIT) \
276 lll_futex_wake (&THREAD_SELF->header.gscope_flag, 1, LLL_PRIVATE); \
277 } \
278 while (0)
279 #define THREAD_GSCOPE_SET_FLAG() \
280 THREAD_SETMEM (THREAD_SELF, header.gscope_flag, THREAD_GSCOPE_FLAG_USED)
281
282 #endif /* __ASSEMBLER__ */
283
284 #endif /* tls.h */