1/* Low-level locking access to futex facilities. Stub version.
2 Copyright (C) 2014-2020 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 _LOWLEVELLOCK_FUTEX_H
20#define _LOWLEVELLOCK_FUTEX_H 1
21
22#ifndef __ASSEMBLER__
23# include <sysdep.h>
24# include <sysdep-cancel.h>
25# include <kernel-features.h>
26#endif
27
28#define FUTEX_WAIT 0
29#define FUTEX_WAKE 1
30#define FUTEX_REQUEUE 3
31#define FUTEX_CMP_REQUEUE 4
32#define FUTEX_WAKE_OP 5
33#define FUTEX_OP_CLEAR_WAKE_IF_GT_ONE ((4 << 24) | 1)
34#define FUTEX_LOCK_PI 6
35#define FUTEX_UNLOCK_PI 7
36#define FUTEX_TRYLOCK_PI 8
37#define FUTEX_WAIT_BITSET 9
38#define FUTEX_WAKE_BITSET 10
39#define FUTEX_WAIT_REQUEUE_PI 11
40#define FUTEX_CMP_REQUEUE_PI 12
41#define FUTEX_PRIVATE_FLAG 128
42#define FUTEX_CLOCK_REALTIME 256
43
44#define FUTEX_BITSET_MATCH_ANY 0xffffffff
45
46/* Values for 'private' parameter of locking macros. Yes, the
47 definition seems to be backwards. But it is not. The bit will be
48 reversed before passing to the system call. */
49#define LLL_PRIVATE 0
50#define LLL_SHARED FUTEX_PRIVATE_FLAG
51
52#ifndef __ASSEMBLER__
53
54# if IS_IN (libc) || IS_IN (rtld)
55/* In libc.so or ld.so all futexes are private. */
56# define __lll_private_flag(fl, private) \
57 ({ \
58 /* Prevent warnings in callers of this macro. */ \
59 int __lll_private_flag_priv __attribute__ ((unused)); \
60 __lll_private_flag_priv = (private); \
61 ((fl) | FUTEX_PRIVATE_FLAG); \
62 })
63# else
64# define __lll_private_flag(fl, private) \
65 (((fl) | FUTEX_PRIVATE_FLAG) ^ (private))
66# endif
67
68# define lll_futex_syscall(nargs, futexp, op, ...) \
69 ({ \
70 long int __ret = INTERNAL_SYSCALL (futex, nargs, futexp, op, \
71 __VA_ARGS__); \
72 (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (__ret)) \
73 ? -INTERNAL_SYSCALL_ERRNO (__ret) : 0); \
74 })
75
76/* For most of these macros, the return value is never really used.
77 Nevertheless, the protocol is that each one returns a negated errno
78 code for failure or zero for success. (Note that the corresponding
79 Linux system calls can sometimes return positive values for success
80 cases too. We never use those values.) */
81
82
83/* Wait while *FUTEXP == VAL for an lll_futex_wake call on FUTEXP. */
84# define lll_futex_wait(futexp, val, private) \
85 lll_futex_timed_wait (futexp, val, NULL, private)
86
87# define lll_futex_timed_wait(futexp, val, timeout, private) \
88 lll_futex_syscall (4, futexp, \
89 __lll_private_flag (FUTEX_WAIT, private), \
90 val, timeout)
91
92/* Verify whether the supplied clockid is supported by
93 lll_futex_clock_wait_bitset. */
94# define lll_futex_supported_clockid(clockid) \
95 ((clockid) == CLOCK_REALTIME || (clockid) == CLOCK_MONOTONIC)
96
97/* The kernel currently only supports CLOCK_MONOTONIC or
98 CLOCK_REALTIME timeouts for FUTEX_WAIT_BITSET. We could attempt to
99 convert others here but currently do not. */
100# define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
101 ({ \
102 long int __ret; \
103 if (lll_futex_supported_clockid (clockid)) \
104 { \
105 const unsigned int clockbit = \
106 (clockid == CLOCK_REALTIME) ? FUTEX_CLOCK_REALTIME : 0; \
107 const int op = \
108 __lll_private_flag (FUTEX_WAIT_BITSET | clockbit, private); \
109 \
110 __ret = lll_futex_syscall (6, futexp, op, val, \
111 timeout, NULL /* Unused. */, \
112 FUTEX_BITSET_MATCH_ANY); \
113 } \
114 else \
115 __ret = -EINVAL; \
116 __ret; \
117 })
118
119/* Wake up up to NR waiters on FUTEXP. */
120# define lll_futex_wake(futexp, nr, private) \
121 lll_futex_syscall (4, futexp, \
122 __lll_private_flag (FUTEX_WAKE, private), nr, 0)
123
124/* Wake up up to NR_WAKE waiters on FUTEXP. Move up to NR_MOVE of the
125 rest from waiting on FUTEXP to waiting on MUTEX (a different futex).
126 Returns non-zero if error happened, zero if success. */
127# define lll_futex_requeue(futexp, nr_wake, nr_move, mutex, val, private) \
128 lll_futex_syscall (6, futexp, \
129 __lll_private_flag (FUTEX_CMP_REQUEUE, private), \
130 nr_wake, nr_move, mutex, val)
131
132/* Wake up up to NR_WAKE waiters on FUTEXP and NR_WAKE2 on FUTEXP2.
133 Returns non-zero if error happened, zero if success. */
134# define lll_futex_wake_unlock(futexp, nr_wake, nr_wake2, futexp2, private) \
135 lll_futex_syscall (6, futexp, \
136 __lll_private_flag (FUTEX_WAKE_OP, private), \
137 nr_wake, nr_wake2, futexp2, \
138 FUTEX_OP_CLEAR_WAKE_IF_GT_ONE)
139
140
141/* Priority Inheritance support. */
142#define lll_futex_timed_lock_pi(futexp, abstime, private) \
143 lll_futex_syscall (4, futexp, \
144 __lll_private_flag (FUTEX_LOCK_PI, private), \
145 0, abstime)
146
147#define lll_futex_timed_unlock_pi(futexp, private) \
148 lll_futex_syscall (4, futexp, \
149 __lll_private_flag (FUTEX_UNLOCK_PI, private), \
150 0, 0)
151
152/* Like lll_futex_wait (FUTEXP, VAL, PRIVATE) but with the expectation
153 that lll_futex_cmp_requeue_pi (FUTEXP, _, _, MUTEX, _, PRIVATE) will
154 be used to do the wakeup. Confers priority-inheritance behavior on
155 the waiter. */
156# define lll_futex_wait_requeue_pi(futexp, val, mutex, private) \
157 lll_futex_timed_wait_requeue_pi (futexp, val, NULL, 0, mutex, private)
158
159/* Like lll_futex_wait_requeue_pi, but with a timeout. */
160# define lll_futex_timed_wait_requeue_pi(futexp, val, timeout, clockbit, \
161 mutex, private) \
162 lll_futex_syscall (5, futexp, \
163 __lll_private_flag (FUTEX_WAIT_REQUEUE_PI \
164 | (clockbit), private), \
165 val, timeout, mutex)
166
167/* Like lll_futex_requeue, but pairs with lll_futex_wait_requeue_pi
168 and inherits priority from the waiter. */
169# define lll_futex_cmp_requeue_pi(futexp, nr_wake, nr_move, mutex, \
170 val, private) \
171 lll_futex_syscall (6, futexp, \
172 __lll_private_flag (FUTEX_CMP_REQUEUE_PI, \
173 private), \
174 nr_wake, nr_move, mutex, val)
175
176/* Like lll_futex_wait, but acting as a cancellable entrypoint. */
177# define lll_futex_wait_cancel(futexp, val, private) \
178 ({ \
179 int __oldtype = CANCEL_ASYNC (); \
180 long int __err = lll_futex_wait (futexp, val, LLL_SHARED); \
181 CANCEL_RESET (__oldtype); \
182 __err; \
183 })
184
185/* Like lll_futex_timed_wait, but acting as a cancellable entrypoint. */
186# define lll_futex_timed_wait_cancel(futexp, val, timeout, private) \
187 ({ \
188 int __oldtype = CANCEL_ASYNC (); \
189 long int __err = lll_futex_timed_wait (futexp, val, timeout, private); \
190 CANCEL_RESET (__oldtype); \
191 __err; \
192 })
193
194#endif /* !__ASSEMBLER__ */
195
196#endif /* lowlevellock-futex.h */
197