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 #include <linux/kernel.h>
  13 #include <linux/posix-timers.h>
  14 #include <linux/time.h>
  15 #include <linux/string.h>
  16 #include <asm/vsyscall.h>
  17 #include <asm/vgtod.h>
  18 #include <asm/timex.h>
  19 #include <asm/hpet.h>
  20 #include <asm/unistd.h>
  21 #include <asm/io.h>
  22 #include <asm/vgtod.h>
  23 #include "vextern.h"
  24
  25 #define gtod vdso_vsyscall_gtod_data
  26
  27 static long vdso_fallback_gettime(long clock, struct timespec *ts)
  28 {
  29         long ret;
  30         asm("syscall" : "=a" (ret) :
  31             "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
  32         return ret;
  33 }
  34
  35 static inline long vgetns(void)
  36 {
  37         long v;
  38         cycles_t (*vread)(void);
  39         vread = gtod->clock.vread;
  40         v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
  41         return (v * gtod->clock.mult) >> gtod->clock.shift;
  42 }
  43
  44 static noinline int do_realtime(struct timespec *ts)
  45 {
  46         unsigned long seq, ns;
  47         do {
  48                 seq = read_seqbegin(&gtod->lock);
  49                 ts->tv_sec = gtod->wall_time_sec;
  50                 ts->tv_nsec = gtod->wall_time_nsec;
  51                 ns = vgetns();
  52         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  53         timespec_add_ns(ts, ns);
  54         return 0;
  55 }
  56
  57 /* Copy of the version in kernel/time.c which we cannot directly access */
  58 static void vset_normalized_timespec(struct timespec *ts, long sec, long nsec)
  59 {
  60         while (nsec >= NSEC_PER_SEC) {
  61                 nsec -= NSEC_PER_SEC;
  62                 ++sec;
  63         }
  64         while (nsec < 0) {
  65                 nsec += NSEC_PER_SEC;
  66                 --sec;
  67         }
  68         ts->tv_sec = sec;
  69         ts->tv_nsec = nsec;
  70 }
  71
  72 static noinline int do_monotonic(struct timespec *ts)
  73 {
  74         unsigned long seq, ns, secs;
  75         do {
  76                 seq = read_seqbegin(&gtod->lock);
  77                 secs = gtod->wall_time_sec;
  78                 ns = gtod->wall_time_nsec + vgetns();
  79                 secs += gtod->wall_to_monotonic.tv_sec;
  80                 ns += gtod->wall_to_monotonic.tv_nsec;
  81         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  82         vset_normalized_timespec(ts, secs, ns);
  83         return 0;
  84 }
  85
  86 int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
  87 {
  88         if (likely(gtod->sysctl_enabled && gtod->clock.vread))
  89                 switch (clock) {
  90                 case CLOCK_REALTIME:
  91                         return do_realtime(ts);
  92                 case CLOCK_MONOTONIC:
  93                         return do_monotonic(ts);
  94                 }
  95         return vdso_fallback_gettime(clock, ts);
  96 }
  97 int clock_gettime(clockid_t, struct timespec *)
  98         __attribute__((weak, alias("__vdso_clock_gettime")));
  99
 100 int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 101 {
 102         long ret;
 103         if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
 104                 BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
 105                              offsetof(struct timespec, tv_nsec) ||
 106                              sizeof(*tv) != sizeof(struct timespec));
 107                 do_realtime((struct timespec *)tv);
 108                 tv->tv_usec /= 1000;
 109                 if (unlikely(tz != NULL)) {
 110                         /* This relies on gcc inlining the memcpy. We'll notice
 111                            if it ever fails to do so. */
 112                         memcpy(tz, &gtod->sys_tz, sizeof(struct timezone));
 113                 }
 114                 return 0;
 115         }
 116         asm("syscall" : "=a" (ret) :
 117             "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 118         return ret;
 119 }
 120 int gettimeofday(struct timeval *, struct timezone *)
 121         __attribute__((weak, alias("__vdso_gettimeofday")));