linux: Consolidate time implementation

The IFUNC bypass to vDSO is used when USE_IFUNC_TIME is set.
Currently powerpc and x86 defines it.  Otherwise the generic
implementation is used, which calls clock_gettime.

Checked on powerpc64le-linux-gnu, powerpc64-linux-gnu,
powerpc-linux-gnu-power4, x86_64-linux-gnu, and i686-linux-gnu.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

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

@@ -16,33 +16,5 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <time.h>
+#define USE_IFUNC_TIME
-#include <sysdep.h>
+#include <sysdeps/unix/sysv/linux/time.c>
-#include <sysdep-vdso.h>
-
-static time_t
-time_vsyscall (time_t *t)
-{
-  return INLINE_VSYSCALL (time, 1, t);
-}
-
-#ifdef SHARED
-# include <dl-vdso.h>
-# include <libc-vdso.h>
-
-# define INIT_ARCH() \
-  void *vdso_time = get_vdso_symbol (HAVE_TIME_VSYSCALL);
-
-/* If the vDSO is not available we fall back to the syscall.  */
-libc_ifunc (time,
-	    vdso_time
-	    ? VDSO_IFUNC_RET (vdso_time)
-	    : (void *) time_vsyscall);
-
-#else
-time_t
-time (time_t *t)
-{
-  return time_vsyscall (t);
-}
-#endif /* !SHARED */

sysdeps/unix/sysv/linux/time.c

@@ -0,0 +1,50 @@
+/* time -- Get number of seconds since Epoch.  Linux version.
+   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; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* Optimize the function call by setting the PLT directly to vDSO symbol.  */
+#ifdef USE_IFUNC_TIME
+# include <time.h>
+# include <sysdep.h>
+# include <sysdep-vdso.h>
+
+#ifdef SHARED
+# include <dl-vdso.h>
+
+static time_t
+time_syscall (time_t *t)
+{
+  return INLINE_SYSCALL_CALL (time, t);
+}
+
+# undef INIT_ARCH
+# define INIT_ARCH() \
+  void *vdso_time = get_vdso_symbol (HAVE_TIME_VSYSCALL);
+libc_ifunc (time,
+	    vdso_time ? VDSO_IFUNC_RET (vdso_time)
+		      : (void *) time_syscall);
+
+# else
+time_t
+time (time_t *t)
+{
+  return INLINE_VSYSCALL (time, 1, t);
+}
+# endif /* !SHARED */
+#else /* USE_IFUNC_TIME  */
+# include <time/time.c>
+#endif

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

@@ -16,28 +16,5 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <time.h>
+#define USE_IFUNC_TIME
-#include <sysdep.h>
+#include <sysdeps/unix/sysv/linux/time.c>
-#include <sysdep-vdso.h>
-
-static time_t
-time_vsyscall (time_t *t)
-{
-  return INLINE_VSYSCALL (time, 1, t);
-}
-
-#ifdef SHARED
-# include <dl-vdso.h>
-# include <libc-vdso.h>
-
-#undef INIT_ARCH
-#define INIT_ARCH()
-/* If the vDSO is not available we fall back on the syscall.  */
-libc_ifunc (time, (get_vdso_symbol ("__vdso_time") ?: time_vsyscall))
-#else
-time_t
-time (time_t *t)
-{
-  return time_vsyscall (t);
-}
-#endif