y2038: linux: Provide __clock_adjtime64 implementation

This patch replaces auto generated wrapper (as described in
sysdeps/unix/sysv/linux/syscalls.list) for clock_adjtime with one which adds
extra support for reading 64 bit time values on machines with __TIMESIZE != 64.

To achieve this goal new __clock_adjtime64 explicit 64 bit function for
adjusting Linux clock has been added.
Moreover, a 32 bit version - __clock_adjtime has been refactored to internally
use __clock_adjtime64.

The __clock_adjtime is now supposed to be used on systems still supporting 32
bit time (__TIMESIZE != 64) - hence the necessary conversions between 64 bit
struct __timespec64 and struct timespec.

The new __clock_adjtime64 syscall available from Linux 5.1+ has been used, when
applicable.
Up till v5.4 in the Linux kernel there was a bug preventing this call from
obtaining correct struct's timex time.tv_sec time after time_t overflow
(i.e. not being Y2038 safe).

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

Linux kernel, headers and minimal kernel version for glibc build test matrix:
- Linux v5.1 (with clock_adjtime64) and glibc build with v5.1 as
  minimal kernel version (--enable-kernel="5.1.0")
  The __ASSUME_TIME64_SYSCALLS flag defined.

- Linux v5.1 and default minimal kernel version
  The __ASSUME_TIME64_SYSCALLS not defined, but kernel supports clock_adjtime64
  syscall.

- Linux v4.19 (no clock_adjtime64 support) with default minimal kernel version
  for contemporary glibc (3.2.0)
  This kernel doesn't support clock_adjtime64 syscall, so the fallback to
  clock_adjtime is tested.

Above tests were performed with Y2038 redirection applied as well as without
(so the __TIMESIZE != 64 execution path is checked as well).

No regressions were observed.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/unix/sysv/linux/Makefile

@@ -60,7 +60,7 @@ sysdep_routines += adjtimex clone umount umount2 readahead sysctl \
 		   personality epoll_wait tee vmsplice splice \
 		   open_by_handle_at mlock2 pkey_mprotect pkey_set pkey_get \
 		   timerfd_gettime timerfd_settime prctl \
-		   process_vm_readv process_vm_writev
+		   process_vm_readv process_vm_writev clock_adjtime
 
 CFLAGS-gethostid.c = -fexceptions
 CFLAGS-tee.c = -fexceptions -fasynchronous-unwind-tables

sysdeps/unix/sysv/linux/clock_adjtime.c

@@ -0,0 +1,73 @@
+/* clock_adjtime -- tune kernel clock.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <time.h>
+#include <sysdep.h>
+#include <sys/timex.h>
+#include <kernel-features.h>
+
+int
+__clock_adjtime64 (const clockid_t clock_id, struct __timex64 *tx64)
+{
+#ifdef __ASSUME_TIME64_SYSCALLS
+# ifndef __NR_clock_adjtime64
+#  define __NR_clock_adjtime64 __NR_clock_adjtime
+# endif
+	return INLINE_SYSCALL_CALL (clock_adjtime64, clock_id, tx64);
+#else
+  int ret = INLINE_SYSCALL_CALL (clock_adjtime64, clock_id, tx64);
+  if (errno != ENOSYS)
+    return ret;
+
+  if (tx64->modes & ADJ_SETOFFSET
+      && ! in_time_t_range (tx64->time.tv_sec))
+    {
+      __set_errno (EOVERFLOW);
+      return -1;
+    }
+
+  struct timex tx32 = valid_timex64_to_timex (*tx64);
+  int retval = INLINE_SYSCALL_CALL (clock_adjtime, clock_id, &tx32);
+  if (retval >= 0)
+    *tx64 = valid_timex_to_timex64 (tx32);
+
+  return retval;
+#endif
+}
+
+#if __TIMESIZE != 64
+libc_hidden_def (__clock_adjtime64)
+
+int
+__clock_adjtime (const clockid_t clock_id, struct timex *tx)
+{
+  struct __timex64 tx64;
+  int retval;
+
+  tx64 = valid_timex_to_timex64 (*tx);
+  retval = __clock_adjtime64 (clock_id, &tx64);
+  if (retval >= 0)
+    *tx = valid_timex64_to_timex (tx64);
+
+  return retval;
+}
+#endif
+libc_hidden_def (__clock_adjtime);
+strong_alias (__clock_adjtime, clock_adjtime)

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

@@ -30,6 +30,7 @@ libc_hidden_proto (__adjtimex)
 /* Local definition of 64 bit time supporting timex struct */
 #  if __TIMESIZE == 64
 #   define __timex64 timex
+#   define __clock_adjtime64 __clock_adjtime
 #  else
 
 struct __timex64
@@ -71,6 +72,8 @@ struct __timex64
   int  :32;
   int  :32;
 };
+extern int __clock_adjtime64 (const clockid_t clock_id, struct __timex64 *tx64);
+libc_hidden_proto (__clock_adjtime64);
 #  endif
 
 /* Convert a known valid struct timex into a struct __timex64.  */

sysdeps/unix/sysv/linux/syscalls.list

@@ -4,7 +4,6 @@ alarm		-	alarm		i:i	alarm
 bdflush		EXTRA	bdflush		i:ii	__compat_bdflush	bdflush@GLIBC_2.0:GLIBC_2.23
 capget		EXTRA	capget		i:pp	capget
 capset		EXTRA	capset		i:pp	capset
-clock_adjtime	EXTRA	clock_adjtime	i:ip	__clock_adjtime		clock_adjtime
 create_module	EXTRA	create_module	3	__compat_create_module	create_module@GLIBC_2.0:GLIBC_2.23
 delete_module	EXTRA	delete_module	3	delete_module
 epoll_create	EXTRA	epoll_create	i:i	epoll_create