1 files changed, 111 insertions, 0 deletions
diff --git a/src/boot/efi/ticks.c b/src/boot/efi/ticks.c
new file mode 100644
index 0000000..873b9fe
--- /dev/null
+++ b/src/boot/efi/ticks.c
@@ -0,0 +1,111 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "ticks.h"
+#include "util.h"
+#include "vmm.h"
+
+#if defined(__i386__) || defined(__x86_64__)
+#  include <cpuid.h>
+
+static uint64_t ticks_read_arch(void) {
+        /* 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;
+
+        return __builtin_ia32_rdtsc();
+}
+
+static uint64_t ticks_freq_arch(void) {
+        /* Detect TSC frequency from CPUID information if available. */
+
+        unsigned max_leaf, ebx, ecx, edx;
+        if (__get_cpuid(0, &max_leaf, &ebx, &ecx, &edx) == 0)
+                return 0;
+
+        /* Leaf 0x15 is Intel only. */
+        if (max_leaf < 0x15 || ebx != signature_INTEL_ebx || ecx != signature_INTEL_ecx ||
+            edx != signature_INTEL_edx)
+                return 0;
+
+        unsigned denominator, numerator, crystal_hz;
+        __cpuid(0x15, denominator, numerator, crystal_hz, edx);
+        if (denominator == 0 || numerator == 0)
+                return 0;
+
+        uint64_t freq = crystal_hz;
+        if (crystal_hz == 0) {
+                /* If the crystal frequency is not available, try to deduce it from
+                 * the processor frequency leaf if available. */
+                if (max_leaf < 0x16)
+                        return 0;
+
+                unsigned core_mhz;
+                __cpuid(0x16, core_mhz, ebx, ecx, edx);
+                freq = core_mhz * 1000ULL * 1000ULL * denominator / numerator;
+        }
+
+        return freq * numerator / denominator;
+}
+
+#elif defined(__aarch64__)
+
+static uint64_t ticks_read_arch(void) {
+        uint64_t val;
+        asm volatile("mrs %0, cntvct_el0" : "=r"(val));
+        return val;
+}
+
+static uint64_t ticks_freq_arch(void) {
+        uint64_t freq;
+        asm volatile("mrs %0, cntfrq_el0" : "=r"(freq));
+        return freq;
+}
+
+#else
+
+static uint64_t ticks_read_arch(void) {
+        return 0;
+}
+
+static uint64_t ticks_freq_arch(void) {
+        return 0;
+}
+
+#endif
+
+static uint64_t ticks_freq(void) {
+        static uint64_t cache = 0;
+
+        if (cache != 0)
+                return cache;
+
+        cache = ticks_freq_arch();
+        if (cache != 0)
+                return cache;
+
+        /* As a fallback, count ticks during a millisecond delay. */
+        uint64_t ticks_start = ticks_read_arch();
+        BS->Stall(1000);
+        uint64_t ticks_end = ticks_read_arch();
+
+        if (ticks_end < ticks_start) /* Check for an overflow (which is not that unlikely, given on some
+                                      * archs the value is 32-bit) */
+                return 0;
+
+        cache = (ticks_end - ticks_start) * 1000UL;
+        return cache;
+}
+
+uint64_t time_usec(void) {
+        uint64_t ticks = ticks_read_arch();
+        if (ticks == 0)
+                return 0;
+
+        uint64_t freq = ticks_freq();
+        if (freq == 0)
+                return 0;
+
+        return 1000UL * 1000UL * ticks / freq;
+}