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1// SPDX-License-Identifier: GPL-2.02 3#include <linux/types.h>4 5#include "../../../util/tsc.h"6 7u64 rdtsc(void)8{9 u64 val;10 11 /*12 * According to ARM DDI 0487F.c, from Armv8.0 to Armv8.5 inclusive, the13 * system counter is at least 56 bits wide; from Armv8.6, the counter14 * must be 64 bits wide. So the system counter could be less than 6415 * bits wide and it is attributed with the flag 'cap_user_time_short'16 * is true.17 */18 asm volatile("mrs %0, cntvct_el0" : "=r" (val));19 20 return val;21}22