Resguardo inicial

linux-7.2.3/tools/perf/arch/arm64/util/tsc.c

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/types.h>
+
+#include "../../../util/tsc.h"
+
+u64 rdtsc(void)
+{
+	u64 val;
+
+	/*
+	 * According to ARM DDI 0487F.c, from Armv8.0 to Armv8.5 inclusive, the
+	 * system counter is at least 56 bits wide; from Armv8.6, the counter
+	 * must be 64 bits wide.  So the system counter could be less than 64
+	 * bits wide and it is attributed with the flag 'cap_user_time_short'
+	 * is true.
+	 */
+	asm volatile("mrs %0, cntvct_el0" : "=r" (val));
+
+	return val;
+}