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 #include "vextern.h"
  26
  27 #define gtod vdso_vsyscall_gtod_data
  28
  29 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
  30 {
  31         long ret;
  32         asm("syscall" : "=a" (ret) :
  33             "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
  34         return ret;
  35 }
  36
  37 notrace static inline long vgetns(void)
  38 {
  39         long v;
  40         cycles_t (*vread)(void);
  41         vread = gtod->clock.vread;
  42         v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
  43         return (v * gtod->clock.mult) >> gtod->clock.shift;
  44 }
  45
  46 notrace static noinline int do_realtime(struct timespec *ts)
  47 {
  48         unsigned long seq, ns;
  49         do {
  50                 seq = read_seqbegin(&gtod->lock);
  51                 ts->tv_sec = gtod->wall_time_sec;
  52                 ts->tv_nsec = gtod->wall_time_nsec;
  53                 ns = vgetns();
  54         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  55         timespec_add_ns(ts, ns);
  56         return 0;
  57 }
  58
  59 /* Copy of the version in kernel/time.c which we cannot directly access */
  60 notrace static void
  61 vset_normalized_timespec(struct timespec *ts, long sec, long nsec)
  62 {
  63         while (nsec >= NSEC_PER_SEC) {
  64                 nsec -= NSEC_PER_SEC;
  65                 ++sec;
  66         }
  67         while (nsec < 0) {
  68                 nsec += NSEC_PER_SEC;
  69                 --sec;
  70         }
  71         ts->tv_sec = sec;
  72         ts->tv_nsec = nsec;
  73 }
  74
  75 notrace static noinline int do_monotonic(struct timespec *ts)
  76 {
  77         unsigned long seq, ns, secs;
  78         do {
  79                 seq = read_seqbegin(&gtod->lock);
  80                 secs = gtod->wall_time_sec;
  81                 ns = gtod->wall_time_nsec + vgetns();
  82                 secs += gtod->wall_to_monotonic.tv_sec;
  83                 ns += gtod->wall_to_monotonic.tv_nsec;
  84         } while (unlikely(read_seqretry(&gtod->lock, seq)));
  85         vset_normalized_timespec(ts, secs, ns);
  86         return 0;
  87 }
  88
  89 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
  90 {
  91         if (likely(gtod->sysctl_enabled && gtod->clock.vread))
  92                 switch (clock) {
  93                 case CLOCK_REALTIME:
  94                         return do_realtime(ts);
  95                 case CLOCK_MONOTONIC:
  96                         return do_monotonic(ts);
  97                 }
  98         return vdso_fallback_gettime(clock, ts);
  99 }
 100 int clock_gettime(clockid_t, struct timespec *)
 101         __attribute__((weak, alias("__vdso_clock_gettime")));
 102
 103 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 104 {
 105         long ret;
 106         if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
 107                 BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
 108                              offsetof(struct timespec, tv_nsec) ||
 109                              sizeof(*tv) != sizeof(struct timespec));
 110                 do_realtime((struct timespec *)tv);
 111                 tv->tv_usec /= 1000;
 112                 if (unlikely(tz != NULL)) {
 113                         /* Avoid memcpy. Some old compilers fail to inline it */
 114                         tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
 115                         tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
 116                 }
 117                 return 0;
 118         }
 119         asm("syscall" : "=a" (ret) :
 120             "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 121         return ret;
 122 }
 123 int gettimeofday(struct timeval *, struct timezone *)
 124         __attribute__((weak, alias("__vdso_gettimeofday")));