src/time/clock_gettime.c

   1 #include <time.h>
   2 #include <errno.h>
   3 #include <stdint.h>
   4 #include "syscall.h"
   5 #include "atomic.h"
   6
   7 #ifdef VDSO_CGT_SYM
   8
   9 static void *volatile vdso_func;
  10
  11 static int cgt_init(clockid_t clk, struct timespec *ts)
  12 {
  13         void *p = __vdsosym(VDSO_CGT_VER, VDSO_CGT_SYM);
  14         int (*f)(clockid_t, struct timespec *) =
  15                 (int (*)(clockid_t, struct timespec *))p;
  16         a_cas_p(&vdso_func, (void *)cgt_init, p);
  17         return f ? f(clk, ts) : -ENOSYS;
  18 }
  19
  20 static void *volatile vdso_func = (void *)cgt_init;
  21
  22 #endif
  23
  24 int __clock_gettime(clockid_t clk, struct timespec *ts)
  25 {
  26         int r;
  27
  28 #ifdef VDSO_CGT_SYM
  29         int (*f)(clockid_t, struct timespec *) =
  30                 (int (*)(clockid_t, struct timespec *))vdso_func;
  31         if (f) {
  32                 r = f(clk, ts);
  33                 if (!r) return r;
  34                 if (r == -EINVAL) return __syscall_ret(r);
  35                 /* Fall through on errors other than EINVAL. Some buggy
  36                  * vdso implementations return ENOSYS for clocks they
  37                  * can't handle, rather than making the syscall. This
  38                  * also handles the case where cgt_init fails to find
  39                  * a vdso function to use. */
  40         }
  41 #endif
  42
  43         r = __syscall(SYS_clock_gettime, clk, ts);
  44         if (r == -ENOSYS) {
  45                 if (clk == CLOCK_REALTIME) {
  46                         __syscall(SYS_gettimeofday, ts, 0);
  47                         ts->tv_nsec = (int)ts->tv_nsec * 1000;
  48                         return 0;
  49                 }
  50                 r = -EINVAL;
  51         }
  52         return __syscall_ret(r);
  53 }
  54
  55 weak_alias(__clock_gettime, clock_gettime);