| 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 | } |