arch/x86/vdso/vclock_gettime.c

   1 /*
   2  * Copyright 2006 Andi Kleen, SUSE Labs.
   3  * Subject to the GNU Public License, v.2
   4  *
   5  * Fast user context implementation of clock_gettime, gettimeofday, and time.
   6  *
   7  * The code should have no internal unresolved relocations.
   8  * Check with readelf after changing.
   9  * Also alternative() doesn't work.
  10  */
  11
  12 /* Disable profiling for userspace code: */
  13 #define DISABLE_BRANCH_PROFILING
  14
  15 #include <linux/kernel.h>
  16 #include <linux/posix-timers.h>
  17 #include <linux/time.h>
  18 #include <linux/string.h>
  19 #include <asm/vsyscall.h>
  20 #include <asm/vgtod.h>
  21 #include <asm/timex.h>
  22 #include <asm/hpet.h>
  23 #include <asm/unistd.h>
  24 #include <asm/io.h>
  25
  26 #define gtod (&VVAR(vsyscall_gtod_data))
  27
  28 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
  29 {
  30         long ret;
  31         asm("syscall" : "=a" (ret) :
  32             "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
  33         return ret;
  34 }
  35
  36 notrace static inline long vgetns(void)
  37 {
  38         long v;
  39         cycles_t (*vread)(void);
  40         vread = gtod->clock.vread;
  41         v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
  42         return (v * gtod->clock.mult) >> gtod->clock.shift;
  43 }
  44
  45 notrace static noinline int do_realtime(struct timespec *ts)
  46 {
  47         unsigned long seq, ns;
  48         do {
  49                 seq = read_seqbegin(&gtod->lock);
  50                 ts->tv_sec = gtod->wall_time_sec;
  51                 ts->tv_nsec = gtod->wall_time_nsec;
  52                 ns = vgetns();
  53         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  54         timespec_add_ns(ts, ns);
  55         return 0;
  56 }
  57
  58 notrace static noinline int do_monotonic(struct timespec *ts)
  59 {
  60         unsigned long seq, ns, secs;
  61         do {
  62                 seq = read_seqbegin(&gtod->lock);
  63                 secs = gtod->wall_time_sec;
  64                 ns = gtod->wall_time_nsec + vgetns();
  65                 secs += gtod->wall_to_monotonic.tv_sec;
  66                 ns += gtod->wall_to_monotonic.tv_nsec;
  67         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  68
  69         /* wall_time_nsec, vgetns(), and wall_to_monotonic.tv_nsec
  70          * are all guaranteed to be nonnegative.
  71          */
  72         while (ns >= NSEC_PER_SEC) {
  73                 ns -= NSEC_PER_SEC;
  74                 ++secs;
  75         }
  76         ts->tv_sec = secs;
  77         ts->tv_nsec = ns;
  78
  79         return 0;
  80 }
  81
  82 notrace static noinline int do_realtime_coarse(struct timespec *ts)
  83 {
  84         unsigned long seq;
  85         do {
  86                 seq = read_seqbegin(&gtod->lock);
  87                 ts->tv_sec = gtod->wall_time_coarse.tv_sec;
  88                 ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
  89         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  90         return 0;
  91 }
  92
  93 notrace static noinline int do_monotonic_coarse(struct timespec *ts)
  94 {
  95         unsigned long seq, ns, secs;
  96         do {
  97                 seq = read_seqbegin(&gtod->lock);
  98                 secs = gtod->wall_time_coarse.tv_sec;
  99                 ns = gtod->wall_time_coarse.tv_nsec;
 100                 secs += gtod->wall_to_monotonic.tv_sec;
 101                 ns += gtod->wall_to_monotonic.tv_nsec;
 102         } while (unlikely(read_seqretry(&gtod->lock, seq)));
 103
 104         /* wall_time_nsec and wall_to_monotonic.tv_nsec are
 105          * guaranteed to be between 0 and NSEC_PER_SEC.
 106          */
 107         if (ns >= NSEC_PER_SEC) {
 108                 ns -= NSEC_PER_SEC;
 109                 ++secs;
 110         }
 111         ts->tv_sec = secs;
 112         ts->tv_nsec = ns;
 113
 114         return 0;
 115 }
 116
 117 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
 118 {
 119         if (likely(gtod->sysctl_enabled))
 120                 switch (clock) {
 121                 case CLOCK_REALTIME:
 122                         if (likely(gtod->clock.vread))
 123                                 return do_realtime(ts);
 124                         break;
 125                 case CLOCK_MONOTONIC:
 126                         if (likely(gtod->clock.vread))
 127                                 return do_monotonic(ts);
 128                         break;
 129                 case CLOCK_REALTIME_COARSE:
 130                         return do_realtime_coarse(ts);
 131                 case CLOCK_MONOTONIC_COARSE:
 132                         return do_monotonic_coarse(ts);
 133                 }
 134         return vdso_fallback_gettime(clock, ts);
 135 }
 136 int clock_gettime(clockid_t, struct timespec *)
 137         __attribute__((weak, alias("__vdso_clock_gettime")));
 138
 139 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 140 {
 141         long ret;
 142         if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
 143                 if (likely(tv != NULL)) {
 144                         BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
 145                                      offsetof(struct timespec, tv_nsec) ||
 146                                      sizeof(*tv) != sizeof(struct timespec));
 147                         do_realtime((struct timespec *)tv);
 148                         tv->tv_usec /= 1000;
 149                 }
 150                 if (unlikely(tz != NULL)) {
 151                         /* Avoid memcpy. Some old compilers fail to inline it */
 152                         tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
 153                         tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
 154                 }
 155                 return 0;
 156         }
 157         asm("syscall" : "=a" (ret) :
 158             "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 159         return ret;
 160 }
 161 int gettimeofday(struct timeval *, struct timezone *)
 162         __attribute__((weak, alias("__vdso_gettimeofday")));
 163
 164 /* This will break when the xtime seconds get inaccurate, but that is
 165  * unlikely */
 166
 167 static __always_inline long time_syscall(long *t)
 168 {
 169         long secs;
 170         asm volatile("syscall"
 171                      : "=a" (secs)
 172                      : "0" (__NR_time), "D" (t) : "cc", "r11", "cx", "memory");
 173         return secs;
 174 }
 175
 176 notrace time_t __vdso_time(time_t *t)
 177 {
 178         time_t result;
 179
 180         if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled))
 181                 return time_syscall(t);
 182
 183         /* This is atomic on x86_64 so we don't need any locks. */
 184         result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);
 185
 186         if (t)
 187                 *t = result;
 188         return result;
 189 }
 190 int time(time_t *t)
 191         __attribute__((weak, alias("__vdso_time")));