arch/x86_64/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         cycles_t (*vread)(void);
  38         vread = gtod->clock.vread;
  39         return ((vread() - gtod->clock.cycle_last) * gtod->clock.mult) >>
  40                 gtod->clock.shift;
  41 }
  42
  43 static noinline int do_realtime(struct timespec *ts)
  44 {
  45         unsigned long seq, ns;
  46         do {
  47                 seq = read_seqbegin(&gtod->lock);
  48                 ts->tv_sec = gtod->wall_time_sec;
  49                 ts->tv_nsec = gtod->wall_time_nsec;
  50                 ns = vgetns();
  51         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  52         timespec_add_ns(ts, ns);
  53         return 0;
  54 }
  55
  56 /* Copy of the version in kernel/time.c which we cannot directly access */
  57 static void vset_normalized_timespec(struct timespec *ts, long sec, long nsec)
  58 {
  59         while (nsec >= NSEC_PER_SEC) {
  60                 nsec -= NSEC_PER_SEC;
  61                 ++sec;
  62         }
  63         while (nsec < 0) {
  64                 nsec += NSEC_PER_SEC;
  65                 --sec;
  66         }
  67         ts->tv_sec = sec;
  68         ts->tv_nsec = nsec;
  69 }
  70
  71 static noinline int do_monotonic(struct timespec *ts)
  72 {
  73         unsigned long seq, ns, secs;
  74         do {
  75                 seq = read_seqbegin(&gtod->lock);
  76                 secs = gtod->wall_time_sec;
  77                 ns = gtod->wall_time_nsec + vgetns();
  78                 secs += gtod->wall_to_monotonic.tv_sec;
  79                 ns += gtod->wall_to_monotonic.tv_nsec;
  80         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  81         vset_normalized_timespec(ts, secs, ns);
  82         return 0;
  83 }
  84
  85 int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
  86 {
  87         if (likely(gtod->sysctl_enabled && gtod->clock.vread))
  88                 switch (clock) {
  89                 case CLOCK_REALTIME:
  90                         return do_realtime(ts);
  91                 case CLOCK_MONOTONIC:
  92                         return do_monotonic(ts);
  93                 }
  94         return vdso_fallback_gettime(clock, ts);
  95 }
  96 int clock_gettime(clockid_t, struct timespec *)
  97         __attribute__((weak, alias("__vdso_clock_gettime")));
  98
  99 int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 100 {
 101         long ret;
 102         if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
 103                 BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
 104                              offsetof(struct timespec, tv_nsec) ||
 105                              sizeof(*tv) != sizeof(struct timespec));
 106                 do_realtime((struct timespec *)tv);
 107                 tv->tv_usec /= 1000;
 108                 if (unlikely(tz != NULL)) {
 109                         /* This relies on gcc inlining the memcpy. We'll notice
 110                            if it ever fails to do so. */
 111                         memcpy(tz, &gtod->sys_tz, sizeof(struct timezone));
 112                 }
 113                 return 0;
 114         }
 115         asm("syscall" : "=a" (ret) :
 116             "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 117         return ret;
 118 }
 119 int gettimeofday(struct timeval *, struct timezone *)
 120         __attribute__((weak, alias("__vdso_gettimeofday")));