Commit | Line | Data |
---|---|---|
d45599f4 MD |
1 | /* |
2 | * compat_arch_x86.c | |
3 | * | |
4 | * Userspace RCU library - x86 compatibility checks | |
5 | * | |
6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | |
7 | * | |
8 | * This library is free software; you can redistribute it and/or | |
9 | * modify it under the terms of the GNU Lesser General Public | |
10 | * License as published by the Free Software Foundation; either | |
11 | * version 2.1 of the License, or (at your option) any later version. | |
12 | * | |
13 | * This library is distributed in the hope that it will be useful, | |
14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
16 | * Lesser General Public License for more details. | |
17 | * | |
18 | * You should have received a copy of the GNU Lesser General Public | |
19 | * License along with this library; if not, write to the Free Software | |
20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
21 | */ | |
22 | ||
23 | #include <stdio.h> | |
24 | #include <pthread.h> | |
25 | #include <signal.h> | |
26 | #include <assert.h> | |
27 | #include <urcu/uatomic_arch.h> | |
28 | ||
29 | /* | |
30 | * It does not really matter if the constructor is called before using | |
31 | * the library, as long as the caller checks if __urcu_cas_avail < 0 and calls | |
32 | * compat_arch_init() explicitely if needed. | |
33 | */ | |
34 | int __attribute__((constructor)) __urcu_cas_init(void); | |
35 | ||
36 | static pthread_mutex_t compat_mutex = PTHREAD_MUTEX_INITIALIZER; | |
37 | ||
38 | /* | |
39 | * -1: unknown | |
40 | * 1: available | |
41 | * 0: unavailable | |
42 | */ | |
43 | int __urcu_cas_avail = -1; | |
44 | ||
45 | /* | |
46 | * Imported from glibc 2.3.5. linuxthreads/sysdeps/i386/pt-machine.h. | |
47 | */ | |
48 | ||
49 | int get_eflags (void) | |
50 | { | |
51 | int res; | |
52 | __asm__ __volatile__ ("pushfl; popl %0" : "=r" (res) : ); | |
53 | return res; | |
54 | } | |
55 | ||
56 | void set_eflags (int newflags) | |
57 | { | |
58 | __asm__ __volatile__ ("pushl %0; popfl" : : "r" (newflags) : "cc"); | |
59 | } | |
60 | ||
61 | int compare_and_swap_is_available (void) | |
62 | { | |
63 | int oldflags = get_eflags (); | |
64 | int changed; | |
65 | /* Flip AC bit in EFLAGS. */ | |
66 | set_eflags (oldflags ^ 0x40000); | |
67 | /* See if bit changed. */ | |
68 | changed = (get_eflags () ^ oldflags) & 0x40000; | |
69 | /* Restore EFLAGS. */ | |
70 | set_eflags (oldflags); | |
71 | /* If the AC flag did not change, it's a 386 and it lacks cmpxchg. | |
72 | Otherwise, it's a 486 or above and it has cmpxchg. */ | |
73 | return changed != 0; | |
74 | } | |
75 | ||
76 | unsigned long _compat_uatomic_cmpxchg(void *addr, unsigned long old, | |
77 | unsigned long _new, int len) | |
78 | { | |
79 | sigset_t newmask, oldmask; | |
80 | int ret; | |
81 | ||
82 | /* Disable signals */ | |
83 | ret = sigemptyset(&newmask); | |
84 | assert(!ret); | |
85 | ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask); | |
86 | assert(!ret); | |
87 | ret = pthread_mutex_lock(&compat_mutex); | |
88 | assert(!ret); | |
89 | ||
90 | switch (len) { | |
91 | case 1: | |
92 | { | |
93 | unsigned char result = *(unsigned char *)addr; | |
94 | if (result == old) | |
95 | *(unsigned char *)addr = (unsigned char)_new; | |
96 | return result; | |
97 | } | |
98 | case 2: | |
99 | { | |
100 | unsigned short result = *(unsigned short *)addr; | |
101 | if (result == old) | |
102 | *(unsigned short *)addr = (unsigned short)_new; | |
103 | return result; | |
104 | } | |
105 | case 4: | |
106 | { | |
107 | unsigned int result = *(unsigned int *)addr; | |
108 | if (result == old) | |
109 | *(unsigned int *)addr = (unsigned int)_new; | |
110 | return result; | |
111 | } | |
112 | } | |
113 | /* generate an illegal instruction. Cannot catch this with linker tricks | |
114 | * when optimizations are disabled. */ | |
115 | __asm__ __volatile__("ud2"); | |
116 | return 0; | |
117 | ||
118 | ret = pthread_mutex_unlock(&compat_mutex); | |
119 | assert(!ret); | |
120 | ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL); | |
121 | assert(!ret); | |
122 | } | |
123 | ||
124 | int __urcu_cas_init(void) | |
125 | { | |
126 | if (__urcu_cas_avail < 0) | |
127 | __urcu_cas_avail = compare_and_swap_is_available(); | |
128 | return __urcu_cas_avail; | |
129 | } |