y2038: linux: Provide __timer_gettime64 implementation

This patch provides new __timer_gettime64 explicit 64 bit function for reading
status of specified timer. To be more precise - the remaining time and interval
set with timer_settime.
Moreover, a 32 bit version - __timer_gettime has been refactored to internally
use __timer_gettime64.

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

The new __timer_gettime64 syscall available from Linux 5.1+ has been used, when
applicable.

The original INLINE_SYSCALL() macro has been replaced with
INLINE_SYSCALL_CALL() to avoid explicit passing the number of arguments.

Build tests:
- The code has been tested on x86_64/x86 (native compilation):
make PARALLELMFLAGS="-j8" && make check PARALLELMFLAGS="-j8" && \\
make xcheck PARALLELMFLAGS="-j8"

- The glibc has been build tested (make PARALLELMFLAGS="-j8") for
x86 (i386), x86_64-x32, and armv7

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

- Use of cross-test-ssh.sh for ARM (armv7):
  make PARALLELMFLAGS="-j8" test-wrapper='./cross-test-ssh.sh root@192.168.7.2' xcheck

Linux kernel, headers and minimal kernel version for glibc build test
matrix:
- Linux v5.1 (with timer_gettime64) 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 timer_gettime64
  syscall.

- Linux v4.19 (no timer_gettime64 support) with default minimal kernel version
  for contemporary glibc (3.2.0)
  This kernel doesn't support timer_gettime64 syscall, so the fallback to
  timer_gettime 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>

include/time.h

@@ -179,6 +179,13 @@ extern int __futimens64 (int fd, const struct __timespec64 tsp[2]);
 libc_hidden_proto (__futimens64);
 #endif
 
+#if __TIMESIZE == 64
+# define __timer_gettime64 __timer_gettime
+#else
+extern int __timer_gettime64 (timer_t timerid, struct __itimerspec64 *value);
+libc_hidden_proto (__timer_gettime64);
+#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/timer_gettime.c

@@ -20,15 +20,51 @@
 #include <stdlib.h>
 #include <time.h>
 #include <sysdep.h>
+#include <kernel-features.h>
 #include "kernel-posix-timers.h"
 
 int
-timer_gettime (timer_t timerid, struct itimerspec *value)
+__timer_gettime64 (timer_t timerid, struct __itimerspec64 *value)
 {
   struct timer *kt = (struct timer *) timerid;
 
-  /* Delete the kernel timer object.  */
-  int res = INLINE_SYSCALL (timer_gettime, 2, kt->ktimerid, value);
+#ifdef __ASSUME_TIME64_SYSCALLS
+# ifndef __NR_timer_gettime64
+#  define __NR_timer_gettime64 __NR_timer_gettime
+# endif
+  return INLINE_SYSCALL_CALL (timer_gettime64, kt->ktimerid, value);
+#else
+# ifdef __NR_timer_gettime64
+  int ret = INLINE_SYSCALL_CALL (timer_gettime64, kt->ktimerid, value);
+  if (ret == 0 || errno != ENOSYS)
+    return ret;
+# endif
+  struct itimerspec its32;
+  int retval = INLINE_SYSCALL_CALL (timer_gettime, kt->ktimerid, &its32);
+  if (retval == 0)
+    {
+      value->it_interval = valid_timespec_to_timespec64 (its32.it_interval);
+      value->it_value = valid_timespec_to_timespec64 (its32.it_value);
+    }
 
-  return res;
+  return retval;
+#endif
 }
+
+#if __TIMESIZE != 64
+int
+__timer_gettime (timer_t timerid, struct itimerspec *value)
+{
+  struct __itimerspec64 its64;
+  int retval = __timer_gettime64 (timerid, &its64);
+  if (retval == 0)
+    {
+      value->it_interval = valid_timespec64_to_timespec (its64.it_interval);
+      value->it_value = valid_timespec64_to_timespec (its64.it_value);
+    }
+
+  return retval;
+}
+#endif
+weak_alias (__timer_gettime, timer_gettime)
+libc_hidden_def (timer_gettime)