y2038: linux: Provide ___adjtimex64 implementation

This patch provides new ___adjtimex64 explicit 64 bit function for adjusting
Linux kernel clock.

Internally, the __clock_adjtime64 syscall is used. This patch is necessary
for having architectures with __WORDSIZE == 32 Y2038 safe.

Moreover, a 32 bit version - ___adjtimex has been refactored to internally
use ___adjtimex64.

The ___adjtimex is now supposed to be used on systems still supporting 32
bit time (__TIMESIZE != 64) - hence the necessary conversions between struct
timex and 64 bit struct __timex64.

Last but not least, in ___adjtimex64 function the __clock_adjtime syscall has
been replaced with __clock_adjtime64 to support 64 bit time on architectures
with __WORDSIZE == 32 and __TIMESIZE != 64.

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 the proper usage of both ___adjtimex64 and ___adjtimex.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/unix/sysv/linux/adjtimex.c

@@ -20,11 +20,28 @@
 #include <sysdep.h>
 
 int
-___adjtimex (struct timex *buf)
+___adjtimex64 (struct __timex64 *tx64)
 {
-  return __clock_adjtime (CLOCK_REALTIME, buf);
+  return __clock_adjtime64 (CLOCK_REALTIME, tx64);
 }
 
+#if __TIMESIZE != 64
+libc_hidden_def (___adjtimex64)
+
+int
+___adjtimex (struct timex *tx)
+{
+  struct __timex64 tx64;
+  int retval;
+
+  tx64 = valid_timex_to_timex64 (*tx);
+  retval = ___adjtimex64 (&tx64);
+  *tx = valid_timex64_to_timex (tx64);
+
+  return retval;
+}
+#endif
+
 #ifdef VERSION_adjtimex
 weak_alias (___adjtimex, __wadjtimex);
 weak_alias (___adjtimex, __wnadjtime);

sysdeps/unix/sysv/linux/include/sys/timex.h

@@ -31,6 +31,7 @@ libc_hidden_proto (__adjtimex)
 #  if __TIMESIZE == 64
 #   define __timex64 timex
 #   define __clock_adjtime64 __clock_adjtime
+#   define ___adjtimex64 ___adjtimex
 #  else
 
 struct __timex64
@@ -74,6 +75,8 @@ struct __timex64
 };
 extern int __clock_adjtime64 (const clockid_t clock_id, struct __timex64 *tx64);
 libc_hidden_proto (__clock_adjtime64);
+extern int ___adjtimex64 (struct __timex64 *tx64);
+libc_hidden_proto (___adjtimex64)
 #  endif
 
 /* Convert a known valid struct timex into a struct __timex64.  */