src/boot/efi/ticks.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <efi.h>
#include <efilib.h>

#include "ticks.h"
#include "util.h"
#include "vmm.h"

#ifdef __x86_64__
static uint64_t ticks_read(void) {
        uint64_t a, d;

        /* The TSC might or might not be virtualized in VMs (and thus might not be accurate or start at zero
         * at boot), depending on hypervisor and CPU functionality. If it's not virtualized it's not useful
         * for keeping time, hence don't attempt to use it. */
        if (in_hypervisor())
                return 0;

        __asm__ volatile ("rdtsc" : "=a" (a), "=d" (d));
        return (d << 32) | a;
}
#elif defined(__i386__)
static uint64_t ticks_read(void) {
        uint64_t val;

        if (in_hypervisor())
                return 0;

        __asm__ volatile ("rdtsc" : "=A" (val));
        return val;
}
#elif defined(__aarch64__)
static uint64_t ticks_read(void) {
        uint64_t val;
        asm volatile("mrs %0, cntvct_el0" : "=r"(val));
        return val;
}
#else
static uint64_t ticks_read(void) {
        return 0;
}
#endif

#if defined(__aarch64__)
static uint64_t ticks_freq(void) {
        uint64_t freq;
        asm volatile("mrs %0, cntfrq_el0" : "=r"(freq));
        return freq;
}
#else
/* count TSC ticks during a millisecond delay */
static uint64_t ticks_freq(void) {
        uint64_t ticks_start, ticks_end;
        static uint64_t cache = 0;

        if (cache != 0)
                return cache;

        ticks_start = ticks_read();
        BS->Stall(1000);
        ticks_end = ticks_read();

        if (ticks_end < ticks_start) /* Check for an overflow (which is not that unlikely, given on some
                                      * archs the value is 32bit) */
                return 0;

        cache = (ticks_end - ticks_start) * 1000UL;
        return cache;
}
#endif

uint64_t time_usec(void) {
        uint64_t ticks, freq;

        ticks = ticks_read();
        if (ticks == 0)
                return 0;

        freq = ticks_freq();
        if (freq == 0)
                return 0;

        return 1000UL * 1000UL * ticks / freq;
}