Use clock_gettime to implement time.

Change the default implementation of time to call clock_gettime,
to align with new Linux ports that are expected to only implement
__NR_clock_gettime.  Arch-specific implementation that either call
the time vDSO or route to gettimeofday vDSO are not removed.

Also for Linux, CLOCK_REALTIME_COARSE is used instead of generic
CLOCK_REALTIME clockid.  This takes less CPU time and its behavior
better matches what the current glibc does.

Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64le-linux-gnu,
powerpc64-linux-gnu, powerpc-linux-gnu, and aarch64-linux-gnu.

Co-authored-by: Zack Weinberg <zackw@panix.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>

4 files changed, 17 insertions, 57 deletions

diff --git a/sysdeps/unix/sysv/linux/time.c b/sysdeps/generic/time-clockid.h
index f461733678..13db6e6b5b 100644
--- a/sysdeps/unix/sysv/linux/time.c
+++ b/sysdeps/generic/time-clockid.h
@@ -1,4 +1,5 @@
-/* Copyright (C) 2005-2019 Free Software Foundation, Inc.
+/* System specific time definitions.  Generic Version.
+   Copyright 2019 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
@@ -15,27 +16,5 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <stddef.h>
-#include <time.h>
-
-#include <sysdep.h>
-
-#ifdef __NR_time
-
-time_t
-time (time_t *t)
-{
-  INTERNAL_SYSCALL_DECL (err);
-  time_t res = INTERNAL_SYSCALL (time, err, 1, NULL);
-  /* There cannot be any error.  */
-  if (t != NULL)
-    *t = res;
-  return res;
-}
-libc_hidden_def (time)
-
-#else
-
-# include <sysdeps/posix/time.c>
-
-#endif
+/* Timer used on clock_gettime for time implementation.  */
+#define TIME_CLOCK_GETTIME_CLOCKID CLOCK_REALTIME
diff --git a/sysdeps/unix/sysv/linux/powerpc/time.c b/sysdeps/unix/sysv/linux/powerpc/time.c
index c35b80fad1..e957b81751 100644
--- a/sysdeps/unix/sysv/linux/powerpc/time.c
+++ b/sysdeps/unix/sysv/linux/powerpc/time.c
@@ -78,6 +78,6 @@ libc_hidden_def (time)
 
 #else
 
-#include <sysdeps/posix/time.c>
+#include <time/time.c>
 
 #endif /* !SHARED */
diff --git a/sysdeps/posix/time.c b/sysdeps/unix/sysv/linux/time-clockid.h
index 0ab31bd7b6..1bdaa18094 100644
--- a/sysdeps/posix/time.c
+++ b/sysdeps/unix/sysv/linux/time-clockid.h
@@ -1,4 +1,5 @@
-/* Copyright (C) 1991-2019 Free Software Foundation, Inc.
+/* System specific time definitions.  Generic Version.
+   Copyright 2019 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
@@ -15,26 +16,7 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <stddef.h>		/* For NULL.  */
-#include <time.h>
-#include <sys/time.h>
-
-
-/* Return the current time as a `time_t' and also put it in *T if T is
-   not NULL.  Time is represented as seconds from Jan 1 00:00:00 1970.  */
-time_t
-time (time_t *t)
-{
-  struct timeval tv;
-  time_t result;
-
-  if (__gettimeofday (&tv, (struct timezone *) NULL))
-    result = (time_t) -1;
-  else
-    result = (time_t) tv.tv_sec;
-
-  if (t != NULL)
-    *t = result;
-  return result;
-}
-libc_hidden_def (time)
+/* Timer used on clock_gettime for time implementation.  For Linux
+   it uses the coarse version which returns the time at the last tick
+   and mimic what time as syscall should return.  */
+#define TIME_CLOCK_GETTIME_CLOCKID CLOCK_REALTIME_COARSE
diff --git a/time/time.c b/time/time.c
index b53a06e29c..e6e5eeff7e 100644
--- a/time/time.c
+++ b/time/time.c
@@ -15,19 +15,18 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
 #include <time.h>
+#include <time-clockid.h>
 
 /* Return the time now, and store it in *TIMER if not NULL.  */
 time_t
 time (time_t *timer)
 {
-  __set_errno (ENOSYS);
+  struct timespec ts;
+  __clock_gettime (TIME_CLOCK_GETTIME_CLOCKID, &ts);
 
-  if (timer != NULL)
-    *timer = (time_t) -1;
-  return (time_t) -1;
+  if (timer)
+    *timer = ts.tv_sec;
+  return ts.tv_sec;
 }
 libc_hidden_def (time)
-
-stub_warning (time)