1 /* Low-level locking access to futex facilities.  Stub version.
2    Copyright (C) 2014-2022 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_LOCK_PI2		13
42 #define FUTEX_PRIVATE_FLAG	128
43 #define FUTEX_CLOCK_REALTIME	256
44 
45 #define FUTEX_BITSET_MATCH_ANY	0xffffffff
46 
47 /* Values for 'private' parameter of locking macros.  Yes, the
48    definition seems to be backwards.  But it is not.  The bit will be
49    reversed before passing to the system call.  */
50 #define LLL_PRIVATE	0
51 #define LLL_SHARED	FUTEX_PRIVATE_FLAG
52 
53 #ifndef __ASSEMBLER__
54 # define __lll_private_flag(fl, private) \
55   (((fl) | FUTEX_PRIVATE_FLAG) ^ (private))
56 
57 # define lll_futex_syscall(nargs, futexp, op, ...)                      \
58   ({                                                                    \
59     long int __ret = INTERNAL_SYSCALL (futex, nargs, futexp, op, 	\
60 				       __VA_ARGS__);                    \
61     (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (__ret))         	\
62      ? -INTERNAL_SYSCALL_ERRNO (__ret) : 0);                     	\
63   })
64 
65 /* For most of these macros, the return value is never really used.
66    Nevertheless, the protocol is that each one returns a negated errno
67    code for failure or zero for success.  (Note that the corresponding
68    Linux system calls can sometimes return positive values for success
69    cases too.  We never use those values.)  */
70 
71 
72 /* Wait while *FUTEXP == VAL for an lll_futex_wake call on FUTEXP.  */
73 # define lll_futex_wait(futexp, val, private) \
74   lll_futex_timed_wait (futexp, val, NULL, private)
75 
76 # define lll_futex_timed_wait(futexp, val, timeout, private)     \
77   lll_futex_syscall (4, futexp,                                 \
78 		     __lll_private_flag (FUTEX_WAIT, private),  \
79 		     val, timeout)
80 
81 /* Verify whether the supplied clockid is supported by
82    lll_futex_clock_wait_bitset.  */
83 # define lll_futex_supported_clockid(clockid)			\
84   ((clockid) == CLOCK_REALTIME || (clockid) == CLOCK_MONOTONIC)
85 
86 /* Wake up up to NR waiters on FUTEXP.  */
87 # define lll_futex_wake(futexp, nr, private)                             \
88   lll_futex_syscall (4, futexp,                                         \
89 		     __lll_private_flag (FUTEX_WAKE, private), nr, 0)
90 
91 /* Wake up up to NR_WAKE waiters on FUTEXP.  Move up to NR_MOVE of the
92    rest from waiting on FUTEXP to waiting on MUTEX (a different futex).
93    Returns non-zero if error happened, zero if success.  */
94 # define lll_futex_requeue(futexp, nr_wake, nr_move, mutex, val, private) \
95   lll_futex_syscall (6, futexp,                                         \
96 		     __lll_private_flag (FUTEX_CMP_REQUEUE, private),   \
97 		     nr_wake, nr_move, mutex, val)
98 
99 /* Wake up up to NR_WAKE waiters on FUTEXP and NR_WAKE2 on FUTEXP2.
100    Returns non-zero if error happened, zero if success.  */
101 # define lll_futex_wake_unlock(futexp, nr_wake, nr_wake2, futexp2, private) \
102   lll_futex_syscall (6, futexp,                                         \
103 		     __lll_private_flag (FUTEX_WAKE_OP, private),       \
104 		     nr_wake, nr_wake2, futexp2,                        \
105 		     FUTEX_OP_CLEAR_WAKE_IF_GT_ONE)
106 
107 
108 #define lll_futex_timed_unlock_pi(futexp, private) 			\
109   lll_futex_syscall (4, futexp,						\
110 		     __lll_private_flag (FUTEX_UNLOCK_PI, private),	\
111 		     0, 0)
112 
113 /* Like lll_futex_requeue, but pairs with lll_futex_wait_requeue_pi
114    and inherits priority from the waiter.  */
115 # define lll_futex_cmp_requeue_pi(futexp, nr_wake, nr_move, mutex,       \
116                                  val, private)                          \
117   lll_futex_syscall (6, futexp,                                         \
118 		     __lll_private_flag (FUTEX_CMP_REQUEUE_PI,          \
119 					 private),                      \
120 		     nr_wake, nr_move, mutex, val)
121 
122 /* Like lll_futex_wait, but acting as a cancellable entrypoint.  */
123 # define lll_futex_wait_cancel(futexp, val, private) \
124   ({                                                                   \
125     int __oldtype = LIBC_CANCEL_ASYNC ();			       \
126     long int __err = lll_futex_wait (futexp, val, LLL_SHARED);	       \
127     LIBC_CANCEL_RESET (__oldtype);				       \
128     __err;							       \
129   })
130 
131 /* Like lll_futex_timed_wait, but acting as a cancellable entrypoint.  */
132 # define lll_futex_timed_wait_cancel(futexp, val, timeout, private) \
133   ({									   \
134     int __oldtype = LIBC_CANCEL_ASYNC ();			       	   \
135     long int __err = lll_futex_timed_wait (futexp, val, timeout, private); \
136     LIBC_CANCEL_RESET (__oldtype);					   \
137     __err;								   \
138   })
139 
140 #endif  /* !__ASSEMBLER__  */
141 
142 #endif  /* lowlevellock-futex.h */
143