clock_gettime.c raw

   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  #ifdef VDSO_CGT32_SYM
  12  static void *volatile vdso_func_32;
  13  static int cgt_time32_wrap(clockid_t clk, struct timespec *ts)
  14  {
  15  	long ts32[2];
  16  	int (*f)(clockid_t, long[2]) =
  17  		(int (*)(clockid_t, long[2]))vdso_func_32;
  18  	int r = f(clk, ts32);
  19  	if (!r) {
  20  		/* Fallback to syscalls if time32 overflowed. Maybe
  21  		 * we lucked out and somehow migrated to a kernel with
  22  		 * time64 syscalls available. */
  23  		if (ts32[0] < 0) {
  24  			a_cas_p(&vdso_func, (void *)cgt_time32_wrap, 0);
  25  			return -ENOSYS;
  26  		}
  27  		ts->tv_sec = ts32[0];
  28  		ts->tv_nsec = ts32[1];
  29  	}
  30  	return r;
  31  }
  32  #endif
  33  
  34  static int cgt_init(clockid_t clk, struct timespec *ts)
  35  {
  36  	void *p = __vdsosym(VDSO_CGT_VER, VDSO_CGT_SYM);
  37  #ifdef VDSO_CGT32_SYM
  38  	if (!p) {
  39  		void *q = __vdsosym(VDSO_CGT32_VER, VDSO_CGT32_SYM);
  40  		if (q) {
  41  			a_cas_p(&vdso_func_32, 0, q);
  42  			p = cgt_time32_wrap;
  43  		}
  44  	}
  45  #endif
  46  	int (*f)(clockid_t, struct timespec *) =
  47  		(int (*)(clockid_t, struct timespec *))p;
  48  	a_cas_p(&vdso_func, (void *)cgt_init, p);
  49  	return f ? f(clk, ts) : -ENOSYS;
  50  }
  51  
  52  static void *volatile vdso_func = (void *)cgt_init;
  53  
  54  #endif
  55  
  56  int __clock_gettime(clockid_t clk, struct timespec *ts)
  57  {
  58  	int r;
  59  
  60  #ifdef VDSO_CGT_SYM
  61  	int (*f)(clockid_t, struct timespec *) =
  62  		(int (*)(clockid_t, struct timespec *))vdso_func;
  63  	if (f) {
  64  		r = f(clk, ts);
  65  		if (!r) return r;
  66  		if (r == -EINVAL) return __syscall_ret(r);
  67  		/* Fall through on errors other than EINVAL. Some buggy
  68  		 * vdso implementations return ENOSYS for clocks they
  69  		 * can't handle, rather than making the syscall. This
  70  		 * also handles the case where cgt_init fails to find
  71  		 * a vdso function to use. */
  72  	}
  73  #endif
  74  
  75  #ifdef SYS_clock_gettime64
  76  	r = -ENOSYS;
  77  	if (sizeof(time_t) > 4)
  78  		r = __syscall(SYS_clock_gettime64, clk, ts);
  79  	if (SYS_clock_gettime == SYS_clock_gettime64 || r!=-ENOSYS)
  80  		return __syscall_ret(r);
  81  	long ts32[2];
  82  	r = __syscall(SYS_clock_gettime, clk, ts32);
  83  	if (r==-ENOSYS && clk==CLOCK_REALTIME) {
  84  		r = __syscall(SYS_gettimeofday, ts32, 0);
  85  		ts32[1] *= 1000;
  86  	}
  87  	if (!r) {
  88  		ts->tv_sec = ts32[0];
  89  		ts->tv_nsec = ts32[1];
  90  		return r;
  91  	}
  92  	return __syscall_ret(r);
  93  #else
  94  	r = __syscall(SYS_clock_gettime, clk, ts);
  95  	if (r == -ENOSYS) {
  96  		if (clk == CLOCK_REALTIME) {
  97  			__syscall(SYS_gettimeofday, ts, 0);
  98  			ts->tv_nsec = (int)ts->tv_nsec * 1000;
  99  			return 0;
 100  		}
 101  		r = -EINVAL;
 102  	}
 103  	return __syscall_ret(r);
 104  #endif
 105  }
 106  
 107  weak_alias(__clock_gettime, clock_gettime);
 108