fusl/src/time/clock_gettime.c

#include <time.h>
#include <errno.h>
#include <stdint.h>
#include "syscall.h"
#include "libc.h"
#include "atomic.h"

#ifdef VDSO_CGT_SYM

void* __vdsosym(const char*, const char*);

static void* volatile vdso_func;

static int cgt_init(clockid_t clk, struct timespec* ts) {
  void* p = __vdsosym(VDSO_CGT_VER, VDSO_CGT_SYM);
  int (*f)(clockid_t, struct timespec*) =
      (int (*)(clockid_t, struct timespec*))p;
  a_cas_p(&vdso_func, (void*)cgt_init, p);
  return f ? f(clk, ts) : -ENOSYS;
}

static void* volatile vdso_func = (void*)cgt_init;

#endif

int __clock_gettime(clockid_t clk, struct timespec* ts) {
  int r;

#ifdef VDSO_CGT_SYM
  int (*f)(clockid_t, struct timespec*) =
      (int (*)(clockid_t, struct timespec*))vdso_func;
  if (f) {
    r = f(clk, ts);
    if (!r)
      return r;
    if (r == -EINVAL)
      return __syscall_ret(r);
    /* Fall through on errors other than EINVAL. Some buggy
     * vdso implementations return ENOSYS for clocks they
     * can't handle, rather than making the syscall. This
     * also handles the case where cgt_init fails to find
     * a vdso function to use. */
  }
#endif

  r = __syscall(SYS_clock_gettime, clk, ts);
  if (r == -ENOSYS) {
    if (clk == CLOCK_REALTIME) {
      __syscall(SYS_gettimeofday, ts, 0);
      ts->tv_nsec = (int)ts->tv_nsec * 1000;
      return 0;
    }
    r = -EINVAL;
  }
  return __syscall_ret(r);
}

weak_alias(__clock_gettime, clock_gettime);