y2038: linux: Provide __gettimeofday64 implementation

In the glibc the gettimeofday can use vDSO (on power and x86 the
USE_IFUNC_GETTIMEOFDAY is defined), gettimeofday syscall or 'default'
___gettimeofday() from ./time/gettime.c (as a fallback).

In this patch the last function (___gettimeofday) has been refactored and
moved to ./sysdeps/unix/sysv/linux/gettimeofday.c to be Linux specific.

The new __gettimeofday64 explicit 64 bit function for getting 64 bit time from
the kernel (by internally calling __clock_gettime64) has been introduced.

Moreover, a 32 bit version - __gettimeofday has been refactored to internally
use __gettimeofday64.

The __gettimeofday is now supposed to be used on systems still supporting 32
bit time (__TIMESIZE != 64) - hence the necessary check for time_t potential
overflow and conversion of struct __timeval64 to 32 bit struct timespec.

The iFUNC vDSO direct call optimization has been removed from both i686 and
powerpc32 (USE_IFUNC_GETTIMEOFDAY is not defined for those architectures
anymore). The Linux kernel does not provide a y2038 safe implementation of
gettimeofday neither it plans to provide it in the future, clock_gettime64
should be used instead. Keeping support for this optimization would require
to handle another build permutation (!__ASSUME_TIME64_SYSCALLS &&
USE_IFUNC_GETTIMEOFDAY) which adds more complexity and has limited use
(since the idea is to eventually have a y2038 safe glibc build).

Build tests:
./src/scripts/build-many-glibcs.py glibcs

Run-time tests:
- 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

Above tests were performed with Y2038 redirection applied as well as without
to test proper usage of both __gettimeofday64 and __gettimeofday.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
[Including some commit message improvement]

include/time.h

@@ -227,10 +227,14 @@ libc_hidden_proto (__sched_rr_get_interval64);
 
 #if __TIMESIZE == 64
 # define __settimeofday64 __settimeofday
+# define __gettimeofday64 __gettimeofday
 #else
 extern int __settimeofday64 (const struct __timeval64 *tv,
                              const struct timezone *tz);
 libc_hidden_proto (__settimeofday64)
+extern int __gettimeofday64 (struct __timeval64 *restrict tv,
+                             void *restrict tz);
+libc_hidden_proto (__gettimeofday64)
 #endif
 
 /* Compute the `struct tm' representation of T,

sysdeps/unix/sysv/linux/gettimeofday.c

@@ -54,5 +54,43 @@ __gettimeofday (struct timeval *restrict tv, void *restrict tz)
 # endif
 weak_alias (__gettimeofday, gettimeofday)
 #else /* USE_IFUNC_GETTIMEOFDAY  */
-# include <time/gettimeofday.c>
+/* Conversion of gettimeofday function to support 64 bit time on archs
+   with __WORDSIZE == 32 and __TIMESIZE == 32/64  */
+#include <errno.h>
+
+int
+__gettimeofday64 (struct __timeval64 *restrict tv, void *restrict tz)
+{
+  if (__glibc_unlikely (tz != 0))
+    memset (tz, 0, sizeof (struct timezone));
+
+  struct __timespec64 ts64;
+  if (__clock_gettime64 (CLOCK_REALTIME, &ts64))
+	  return -1;
+
+  *tv = timespec64_to_timeval64 (ts64);
+  return 0;
+}
+
+# if __TIMESIZE != 64
+libc_hidden_def (__gettimeofday64)
+
+int
+__gettimeofday (struct timeval *restrict tv, void *restrict tz)
+{
+  struct __timeval64 tv64;
+  if (__gettimeofday64 (&tv64, tz))
+	  return -1;
+
+  if (! in_time_t_range (tv64.tv_sec))
+    {
+      __set_errno (EOVERFLOW);
+      return -1;
+    }
+
+  *tv = valid_timeval64_to_timeval (tv64);
+  return 0;
+}
+# endif
+weak_alias (__gettimeofday, gettimeofday)
 #endif

sysdeps/unix/sysv/linux/powerpc/gettimeofday.c

@@ -15,5 +15,7 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#define USE_IFUNC_GETTIMEOFDAY
+#ifdef __powerpc64__
+# define USE_IFUNC_GETTIMEOFDAY
+#endif
 #include <sysdeps/unix/sysv/linux/gettimeofday.c>

sysdeps/unix/sysv/linux/x86/gettimeofday.c

@@ -16,5 +16,7 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#define USE_IFUNC_GETTIMEOFDAY
+#ifdef __x86_64__
+# define USE_IFUNC_GETTIMEOFDAY
+#endif
 #include <sysdeps/unix/sysv/linux/gettimeofday.c>