root/arch/x86/vdso/vclock_gettime.c

DEFINITIONS

1. vdso_fallback_gettime
2. vgetns
3. do_realtime
4. vset_normalized_timespec
5. do_monotonic
6. __vdso_clock_gettime
7. __vdso_gettimeofday

/*
 * Copyright 2006 Andi Kleen, SUSE Labs.
 * Subject to the GNU Public License, v.2
 *
 * Fast user context implementation of clock_gettime and gettimeofday.
 *
 * The code should have no internal unresolved relocations.
 * Check with readelf after changing.
 * Also alternative() doesn't work.
 */

#include <linux/kernel.h>
#include <linux/posix-timers.h>
#include <linux/time.h>
#include <linux/string.h>
#include <asm/vsyscall.h>
#include <asm/vgtod.h>
#include <asm/timex.h>
#include <asm/hpet.h>
#include <asm/unistd.h>
#include <asm/io.h>
#include "vextern.h"

#define gtod vdso_vsyscall_gtod_data

notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
        long ret;
        asm("syscall" : "=a" (ret) :
            "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
        return ret;
}

notrace static inline long vgetns(void)
{
        long v;
        cycles_t (*vread)(void);
        vread = gtod->clock.vread;
        v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
        return (v * gtod->clock.mult) >> gtod->clock.shift;
}

notrace static noinline int do_realtime(struct timespec *ts)
{
        unsigned long seq, ns;
        do {
                seq = read_seqbegin(&gtod->lock);
                ts->tv_sec = gtod->wall_time_sec;
                ts->tv_nsec = gtod->wall_time_nsec;
                ns = vgetns();
        } while (unlikely(read_seqretry(&gtod->lock, seq)));
        timespec_add_ns(ts, ns);
        return 0;
}

/* Copy of the version in kernel/time.c which we cannot directly access */
notrace static void
vset_normalized_timespec(struct timespec *ts, long sec, long nsec)
{
        while (nsec >= NSEC_PER_SEC) {
                nsec -= NSEC_PER_SEC;
                ++sec;
        }
        while (nsec < 0) {
                nsec += NSEC_PER_SEC;
                --sec;
        }
        ts->tv_sec = sec;
        ts->tv_nsec = nsec;
}

notrace static noinline int do_monotonic(struct timespec *ts)
{
        unsigned long seq, ns, secs;
        do {
                seq = read_seqbegin(&gtod->lock);
                secs = gtod->wall_time_sec;
                ns = gtod->wall_time_nsec + vgetns();
                secs += gtod->wall_to_monotonic.tv_sec;
                ns += gtod->wall_to_monotonic.tv_nsec;
        } while (unlikely(read_seqretry(&gtod->lock, seq)));
        vset_normalized_timespec(ts, secs, ns);
        return 0;
}

notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
        if (likely(gtod->sysctl_enabled && gtod->clock.vread))
                switch (clock) {
                case CLOCK_REALTIME:
                        return do_realtime(ts);
                case CLOCK_MONOTONIC:
                        return do_monotonic(ts);
                }
        return vdso_fallback_gettime(clock, ts);
}
int clock_gettime(clockid_t, struct timespec *)
        __attribute__((weak, alias("__vdso_clock_gettime")));

notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
{
        long ret;
        if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
                BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
                             offsetof(struct timespec, tv_nsec) ||
                             sizeof(*tv) != sizeof(struct timespec));
                do_realtime((struct timespec *)tv);
                tv->tv_usec /= 1000;
                if (unlikely(tz != NULL)) {
                        /* Avoid memcpy. Some old compilers fail to inline it */
                        tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
                        tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
                }
                return 0;
        }
        asm("syscall" : "=a" (ret) :
            "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
        return ret;
}
int gettimeofday(struct timeval *, struct timezone *)
        __attribute__((weak, alias("__vdso_gettimeofday")));