AArch64: Add hp-timing.h

Add hp-timing.h using the cntvct_el0 counter. Return timing in nanoseconds
so it is fully compatible with generic hp-timing. Don't set HP_TIMING_INLINE
in the dynamic linker since it adds unnecessary overheads and some ancient
kernels may not handle emulating cntcvt correctly. Currently cntvct_el0 is
only used for timing in the benchtests.

Reviewed-by: Szabolcs Nagy  <szabolcs.nagy@arm.com>

sysdeps/aarch64/hp-timing.h

@@ -0,0 +1,47 @@
+/* High precision, low overhead timing functions.  AArch64 version.
+   Copyright (C) 2021 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/>.  */
+
+#ifndef _HP_TIMING_H
+#define _HP_TIMING_H	1
+
+#include <time.h>
+#include <stdint.h>
+#include <hp-timing-common.h>
+#include <libc-symbols.h>
+
+/* Don't use inline timer in ld.so.  */
+#if IS_IN(rtld)
+# define HP_TIMING_INLINE	(0)
+#else
+# define HP_TIMING_INLINE	(1)
+#endif
+
+typedef uint64_t hp_timing_t;
+
+#define HP_TIMING_NOW(var) \
+  __asm__ __volatile__ ("isb; mrs %0, cntvct_el0" : "=r" (var))
+
+/* Compute elapsed time in nanoseconds.  */
+#undef HP_TIMING_DIFF
+#define HP_TIMING_DIFF(Diff, Start, End)			\
+({  hp_timing_t freq;						\
+    __asm__ __volatile__ ("mrs %0, cntfrq_el0" : "=r" (freq));	\
+   (Diff) = ((End) - (Start)) * (UINT64_C(1000000000) / freq);	\
+})
+
+#endif	/* hp-timing.h */