y2038: linux: Provide __clock_settime64 implementation

This patch provides new __clock_settime64 explicit 64 bit function for
setting the time. Moreover, a 32 bit version - __clock_settime - has been
refactored to internally use __clock_settime64.

The __clock_settime is now supposed to be used on systems still supporting
32 bit time (__TIMESIZE != 64) - hence the necessary conversion to 64 bit
struct timespec.

The new clock_settime64 syscall available from Linux 5.1+ has been used,
when applicable.

The __ASSUME_TIME64_SYSCALLS flag indicates if the Linux kernel supports
64 bit version of clock_settime (i.e. clock_settime64).
If this flag is not defined, the fallback with legacy clock_settime
supporting 32 bit time is used.

When working on 32 bit systems without Y2038 time support the
clock_settime64 returns error when one wants to set time with wrong
(overflowed) tv_sec value. Moreover, the correctness of tv_nsec is also
checked.

In this patch the internal padding (tv_pad) of struct __timespec64 is
left untouched (on systems with __WORDSIZE == 32) as Linux kernel ignores
upper 32 bits of tv_nsec.

Tests:
- The code has been tested with x86_64/x86 (native compilation):
make PARALLELMFLAGS="-j8" && make xcheck PARALLELMFLAGS="-j8"

- Run specific tests on ARM/x86 32bit systems (qemu):
https://github.com/lmajewski/meta-y2038
and run tests:
https://github.com/lmajewski/y2038-tests/commits/master
on kernels with and without 64 bit time support.

No regressions were observed.

* include/time.h (__clock_settime64):
  Add __clock_settime alias according to __TIMESIZE define
* sysdeps/unix/sysv/linux/clock_settime.c (__clock_settime):
  Refactor this function to be used only on 32 bit machines as a wrapper
  on __clock_settime64.
* sysdeps/unix/sysv/linux/clock_settime.c (__clock_settime64): Add
* sysdeps/unix/sysv/linux/clock_settime.c (__clock_settime64):
  Use clock_settime64 kernel syscall (available from 5.1-rc1+ Linux)


---
Changes for v5:
- Use __ASSUME_TIME64_SYSCALLS to indicate Linux kernel support for 64 bit
  time.
- Move the in_time_t_range() check to __clock_settime64
- Alias __NR_clock_settime64 to __NR_clock_settime if the former is not
  defined in the headers.

Changes for v4:
- __ASSUME_TIME64_SYSCALLS for fall back path
- Use __SYSCALL_WORDSIZE to exclude 'x32' from execution path (so it will
  use x86_64 syscall
- Rewrite the commit message

Changes for v3:
- Rename __ASSUME_64BIT_TIME to __ASSUME_TIME64_SYSCALLS
- Refactor in-code comment (add information regarding Linux kernel ignorance
  of padding
- Do not use __TIMESIZE to select main execution path (for Y2038 systems
  __TIMESIZE would be changed from 32 to 64 bits at some point to indicate
  full Y2038 support

Changes for v2:
- Add support for __ASSUME_64BIT_TIME flag when Linux kernel provides syscalls
  supporting 64 bit time on 32 bit systems
- Provide fallback to 32 bit version of clock_settime when clock_settime64
  is not available
- Do not copy *tp to timespec - this seems like an overkill as in clock_settime()
  the 32 bit struct timespec is copied to internal 64 bit struct __timespec64

include/time.h

@@ -127,6 +127,14 @@ extern __time64_t __timegm64 (struct tm *__tp) __THROW;
 libc_hidden_proto (__timegm64)
 #endif
 
+#if __TIMESIZE == 64
+# define __clock_settime64 __clock_settime
+#else
+extern int __clock_settime64 (clockid_t clock_id,
+                              const struct __timespec64 *tp);
+libc_hidden_proto (__clock_settime64)
+#endif
+
 /* Compute the `struct tm' representation of T,
    offset OFFSET seconds east of UTC,
    and store year, yday, mon, mday, wday, hour, min, sec into *TP.

sysdeps/unix/sysv/linux/clock_settime.c

@@ -19,11 +19,9 @@
 #include <sysdep.h>
 #include <time.h>
 
-#include "kernel-posix-cpu-timers.h"
-
 /* Set CLOCK to value TP.  */
 int
-__clock_settime (clockid_t clock_id, const struct timespec *tp)
+__clock_settime64 (clockid_t clock_id, const struct __timespec64 *tp)
 {
   /* Make sure the time cvalue is OK.  */
   if (tp->tv_nsec < 0 || tp->tv_nsec >= 1000000000)
@@ -32,6 +30,37 @@ __clock_settime (clockid_t clock_id, const struct timespec *tp)
       return -1;
     }
 
-  return INLINE_SYSCALL_CALL (clock_settime, clock_id, tp);
+#ifdef __ASSUME_TIME64_SYSCALLS
+# ifndef __NR_clock_settime64
+#  define __NR_clock_settime64 __NR_clock_settime
+# endif
+  return INLINE_SYSCALL_CALL (clock_settime64, clock_id, tp);
+#else
+# ifdef __NR_clock_settime64
+  int ret = INLINE_SYSCALL_CALL (clock_settime64, clock_id, tp);
+  if (ret == 0 || errno != ENOSYS)
+    return ret;
+# endif
+  if (! in_time_t_range (tp->tv_sec))
+    {
+      __set_errno (EOVERFLOW);
+      return -1;
+    }
+
+  struct timespec ts32;
+  valid_timespec64_to_timespec (tp, &ts32);
+  return INLINE_SYSCALL_CALL (clock_settime, clock_id, &ts32);
+#endif
 }
 weak_alias (__clock_settime, clock_settime)
+
+#if __TIMESIZE != 64
+int
+__clock_settime (clockid_t clock_id, const struct timespec *tp)
+{
+  struct __timespec64 ts64;
+
+  valid_timespec_to_timespec64 (tp, &ts64);
+  return __clock_settime64 (clock_id, &ts64);
+}
+#endif