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 and gettimeofday.
   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 /* Copy of the version in kernel/time.c which we cannot directly access */
  59 notrace static void
  60 vset_normalized_timespec(struct timespec *ts, long sec, long nsec)
  61 {
  62         while (nsec >= NSEC_PER_SEC) {
  63                 nsec -= NSEC_PER_SEC;
  64                 ++sec;
  65         }
  66         while (nsec < 0) {
  67                 nsec += NSEC_PER_SEC;
  68                 --sec;
  69         }
  70         ts->tv_sec = sec;
  71         ts->tv_nsec = nsec;
  72 }
  73
  74 notrace static noinline int do_monotonic(struct timespec *ts)
  75 {
  76         unsigned long seq, ns, secs;
  77         do {
  78                 seq = read_seqbegin(&gtod->lock);
  79                 secs = gtod->wall_time_sec;
  80                 ns = gtod->wall_time_nsec + vgetns();
  81                 secs += gtod->wall_to_monotonic.tv_sec;
  82                 ns += gtod->wall_to_monotonic.tv_nsec;
  83         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  84         vset_normalized_timespec(ts, secs, ns);
  85         return 0;
  86 }
  87
  88 notrace static noinline int do_realtime_coarse(struct timespec *ts)
  89 {
  90         unsigned long seq;
  91         do {
  92                 seq = read_seqbegin(&gtod->lock);
  93                 ts->tv_sec = gtod->wall_time_coarse.tv_sec;
  94                 ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
  95         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  96         return 0;
  97 }
  98
  99 notrace static noinline int do_monotonic_coarse(struct timespec *ts)
 100 {
 101         unsigned long seq, ns, secs;
 102         do {
 103                 seq = read_seqbegin(&gtod->lock);
 104                 secs = gtod->wall_time_coarse.tv_sec;
 105                 ns = gtod->wall_time_coarse.tv_nsec;
 106                 secs += gtod->wall_to_monotonic.tv_sec;
 107                 ns += gtod->wall_to_monotonic.tv_nsec;
 108         } while (unlikely(read_seqretry(&gtod->lock, seq)));
 109         vset_normalized_timespec(ts, secs, ns);
 110         return 0;
 111 }
 112
 113 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
 114 {
 115         if (likely(gtod->sysctl_enabled))
 116                 switch (clock) {
 117                 case CLOCK_REALTIME:
 118                         if (likely(gtod->clock.vread))
 119                                 return do_realtime(ts);
 120                         break;
 121                 case CLOCK_MONOTONIC:
 122                         if (likely(gtod->clock.vread))
 123                                 return do_monotonic(ts);
 124                         break;
 125                 case CLOCK_REALTIME_COARSE:
 126                         return do_realtime_coarse(ts);
 127                 case CLOCK_MONOTONIC_COARSE:
 128                         return do_monotonic_coarse(ts);
 129                 }
 130         return vdso_fallback_gettime(clock, ts);
 131 }
 132 int clock_gettime(clockid_t, struct timespec *)
 133         __attribute__((weak, alias("__vdso_clock_gettime")));
 134
 135 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 136 {
 137         long ret;
 138         if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
 139                 if (likely(tv != NULL)) {
 140                         BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
 141                                      offsetof(struct timespec, tv_nsec) ||
 142                                      sizeof(*tv) != sizeof(struct timespec));
 143                         do_realtime((struct timespec *)tv);
 144                         tv->tv_usec /= 1000;
 145                 }
 146                 if (unlikely(tz != NULL)) {
 147                         /* Avoid memcpy. Some old compilers fail to inline it */
 148                         tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
 149                         tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
 150                 }
 151                 return 0;
 152         }
 153         asm("syscall" : "=a" (ret) :
 154             "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 155         return ret;
 156 }
 157 int gettimeofday(struct timeval *, struct timezone *)
 158         __attribute__((weak, alias("__vdso_gettimeofday")));