1/* Low-level locking access to futex facilities. Stub version.
2 Copyright (C) 2014-2021 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/* Wake up up to NR waiters on FUTEXP. */
98# define lll_futex_wake(futexp, nr, private) \
99 lll_futex_syscall (4, futexp, \
100 __lll_private_flag (FUTEX_WAKE, private), nr, 0)
101
102/* Wake up up to NR_WAKE waiters on FUTEXP. Move up to NR_MOVE of the
103 rest from waiting on FUTEXP to waiting on MUTEX (a different futex).
104 Returns non-zero if error happened, zero if success. */
105# define lll_futex_requeue(futexp, nr_wake, nr_move, mutex, val, private) \
106 lll_futex_syscall (6, futexp, \
107 __lll_private_flag (FUTEX_CMP_REQUEUE, private), \
108 nr_wake, nr_move, mutex, val)
109
110/* Wake up up to NR_WAKE waiters on FUTEXP and NR_WAKE2 on FUTEXP2.
111 Returns non-zero if error happened, zero if success. */
112# define lll_futex_wake_unlock(futexp, nr_wake, nr_wake2, futexp2, private) \
113 lll_futex_syscall (6, futexp, \
114 __lll_private_flag (FUTEX_WAKE_OP, private), \
115 nr_wake, nr_wake2, futexp2, \
116 FUTEX_OP_CLEAR_WAKE_IF_GT_ONE)
117
118
119#define lll_futex_timed_unlock_pi(futexp, private) \
120 lll_futex_syscall (4, futexp, \
121 __lll_private_flag (FUTEX_UNLOCK_PI, private), \
122 0, 0)
123
124/* Like lll_futex_requeue, but pairs with lll_futex_wait_requeue_pi
125 and inherits priority from the waiter. */
126# define lll_futex_cmp_requeue_pi(futexp, nr_wake, nr_move, mutex, \
127 val, private) \
128 lll_futex_syscall (6, futexp, \
129 __lll_private_flag (FUTEX_CMP_REQUEUE_PI, \
130 private), \
131 nr_wake, nr_move, mutex, val)
132
133/* Like lll_futex_wait, but acting as a cancellable entrypoint. */
134# define lll_futex_wait_cancel(futexp, val, private) \
135 ({ \
136 int __oldtype = CANCEL_ASYNC (); \
137 long int __err = lll_futex_wait (futexp, val, LLL_SHARED); \
138 CANCEL_RESET (__oldtype); \
139 __err; \
140 })
141
142/* Like lll_futex_timed_wait, but acting as a cancellable entrypoint. */
143# define lll_futex_timed_wait_cancel(futexp, val, timeout, private) \
144 ({ \
145 int __oldtype = CANCEL_ASYNC (); \
146 long int __err = lll_futex_timed_wait (futexp, val, timeout, private); \
147 CANCEL_RESET (__oldtype); \
148 __err; \
149 })
150
151#endif /* !__ASSEMBLER__ */
152
153#endif /* lowlevellock-futex.h */
154