linux/arch/x86/vdso/vclock_gettime.c
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   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 "vextern.h"
  23
  24#define gtod vdso_vsyscall_gtod_data
  25
  26notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
  27{
  28        long ret;
  29        asm("syscall" : "=a" (ret) :
  30            "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
  31        return ret;
  32}
  33
  34notrace static inline long vgetns(void)
  35{
  36        long v;
  37        cycles_t (*vread)(void);
  38        vread = gtod->clock.vread;
  39        v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
  40        return (v * gtod->clock.mult) >> gtod->clock.shift;
  41}
  42
  43notrace 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 */
  57notrace static void
  58vset_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
  72notrace 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
  86notrace 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}
  97int clock_gettime(clockid_t, struct timespec *)
  98        __attribute__((weak, alias("__vdso_clock_gettime")));
  99
 100notrace 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                        /* Avoid memcpy. Some old compilers fail to inline it */
 111                        tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
 112                        tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
 113                }
 114                return 0;
 115        }
 116        asm("syscall" : "=a" (ret) :
 117            "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 118        return ret;
 119}
 120int gettimeofday(struct timeval *, struct timezone *)
 121        __attribute__((weak, alias("__vdso_gettimeofday")));
 122