compat_arch_x86.c

   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 __rcu_cas_avail < 0 and calls
  32  * compat_arch_init() explicitely if needed.
  33  */
  34 int __attribute__((constructor)) __rcu_cas_init(void);
  35
  36 /*
  37  * -1: unknown
  38  *  1: available
  39  *  0: unavailable
  40  */
  41 int __rcu_cas_avail = -1;
  42
  43 static pthread_mutex_t compat_mutex = PTHREAD_MUTEX_INITIALIZER;
  44
  45 /*
  46  * get_eflags/set_eflags/compare_and_swap_is_available imported from glibc
  47  * 2.3.5. linuxthreads/sysdeps/i386/pt-machine.h.
  48  */
  49
  50 static int get_eflags (void)
  51 {
  52         int res;
  53         __asm__ __volatile__ ("pushfl; popl %0" : "=r" (res) : );
  54         return res;
  55 }
  56
  57 static void set_eflags (int newflags)
  58 {
  59         __asm__ __volatile__ ("pushl %0; popfl" : : "r" (newflags) : "cc");
  60 }
  61
  62 static int compare_and_swap_is_available (void)
  63 {
  64         int oldflags = get_eflags ();
  65         int changed;
  66         /* Flip AC bit in EFLAGS.  */
  67         set_eflags (oldflags ^ 0x40000);
  68         /* See if bit changed.  */
  69         changed = (get_eflags () ^ oldflags) & 0x40000;
  70         /* Restore EFLAGS.  */
  71         set_eflags (oldflags);
  72         /* If the AC flag did not change, it's a 386 and it lacks cmpxchg.
  73         Otherwise, it's a 486 or above and it has cmpxchg.  */
  74         return changed != 0;
  75 }
  76
  77 static void mutex_lock_signal_save(pthread_mutex_t *mutex, sigset_t *oldmask)
  78 {
  79         sigset_t newmask;
  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
  91 static void mutex_lock_signal_restore(pthread_mutex_t *mutex, sigset_t *oldmask)
  92 {
  93         int ret;
  94
  95         ret = pthread_mutex_unlock(&compat_mutex);
  96         assert(!ret);
  97         ret = pthread_sigmask(SIG_SETMASK, oldmask, NULL);
  98         assert(!ret);
  99 }
 100
 101 unsigned long _compat_uatomic_set(void *addr, unsigned long _new, int len)
 102 {
 103         sigset_t mask;
 104         unsigned long result;
 105
 106         mutex_lock_signal_save(&compat_mutex, &mask);
 107         switch (len) {
 108         case 1:
 109                 *(unsigned char *)addr = (unsigned char)_new;
 110                 result = *(unsigned char *)addr;
 111                 break;
 112         case 2:
 113                 *(unsigned short *)addr = (unsigned short)_new;
 114                 result = *(unsigned short *)addr;
 115                 break;
 116         case 4:
 117                 *(unsigned int *)addr = (unsigned int)_new;
 118                 result = *(unsigned int *)addr;
 119                 break;
 120         default:
 121                 /*
 122                  * generate an illegal instruction. Cannot catch this with
 123                  * linker tricks when optimizations are disabled.
 124                  */
 125                 __asm__ __volatile__("ud2");
 126         }
 127         mutex_lock_signal_restore(&compat_mutex, &mask);
 128         return _new;
 129 }
 130
 131 unsigned long _compat_uatomic_xchg(void *addr, unsigned long _new, int len)
 132 {
 133         sigset_t mask;
 134         unsigned long retval;
 135
 136         mutex_lock_signal_save(&compat_mutex, &mask);
 137         switch (len) {
 138         case 1:
 139                 retval = *(unsigned char *)addr;
 140                 *(unsigned char *)addr = (unsigned char)_new;
 141                 break;
 142         case 2:
 143                 retval = *(unsigned short *)addr;
 144                 *(unsigned short *)addr = (unsigned short)_new;
 145                 break;
 146         case 4:
 147                 retval = *(unsigned int *)addr;
 148                 *(unsigned int *)addr = (unsigned int)_new;
 149                 break;
 150         default:
 151                 /*
 152                  * generate an illegal instruction. Cannot catch this with
 153                  * linker tricks when optimizations are disabled.
 154                  */
 155                 __asm__ __volatile__("ud2");
 156         }
 157         mutex_lock_signal_restore(&compat_mutex, &mask);
 158         return retval;
 159 }
 160
 161 unsigned long _compat_uatomic_cmpxchg(void *addr, unsigned long old,
 162                                       unsigned long _new, int len)
 163 {
 164         unsigned long retval;
 165         sigset_t mask;
 166
 167         mutex_lock_signal_save(&compat_mutex, &mask);
 168         switch (len) {
 169         case 1:
 170         {
 171                 unsigned char result = *(unsigned char *)addr;
 172                 if (result == (unsigned char)old)
 173                         *(unsigned char *)addr = (unsigned char)_new;
 174                 retval = result;
 175                 break;
 176         }
 177         case 2:
 178         {
 179                 unsigned short result = *(unsigned short *)addr;
 180                 if (result == (unsigned short)old)
 181                         *(unsigned short *)addr = (unsigned short)_new;
 182                 retval = result;
 183                 break;
 184         }
 185         case 4:
 186         {
 187                 unsigned int result = *(unsigned int *)addr;
 188                 if (result == (unsigned int)old)
 189                         *(unsigned int *)addr = (unsigned int)_new;
 190                 retval = result;
 191                 break;
 192         }
 193         default:
 194                 /*
 195                  * generate an illegal instruction. Cannot catch this with
 196                  * linker tricks when optimizations are disabled.
 197                  */
 198                 __asm__ __volatile__("ud2");
 199         }
 200         mutex_lock_signal_restore(&compat_mutex, &mask);
 201         return retval;
 202 }
 203
 204 unsigned long _compat_uatomic_add_return(void *addr, unsigned long v, int len)
 205 {
 206         sigset_t mask;
 207         unsigned long result;
 208
 209         mutex_lock_signal_save(&compat_mutex, &mask);
 210         switch (len) {
 211         case 1:
 212                 *(unsigned char *)addr += (unsigned char)v;
 213                 result = *(unsigned char *)addr;
 214                 break;
 215         case 2:
 216                 *(unsigned short *)addr += (unsigned short)v;
 217                 result = *(unsigned short *)addr;
 218                 break;
 219         case 4:
 220                 *(unsigned int *)addr += (unsigned int)v;
 221                 result = *(unsigned int *)addr;
 222                 break;
 223         default:
 224                 /*
 225                  * generate an illegal instruction. Cannot catch this with
 226                  * linker tricks when optimizations are disabled.
 227                  */
 228                 __asm__ __volatile__("ud2");
 229         }
 230         mutex_lock_signal_restore(&compat_mutex, &mask);
 231         return result;
 232 }
 233
 234 int __rcu_cas_init(void)
 235 {
 236         if (__rcu_cas_avail < 0)
 237                 __rcu_cas_avail = compare_and_swap_is_available();
 238         return __rcu_cas_avail;
 239 }