x86_64: rdstc

arm: attempt pmccntr, but didn't work, TODO why: no QEMU support?

kernel_module/user/README.adoc

@@ -20,6 +20,7 @@ These programs can also be compiled and used on host.
 .... link:init_dev_kmsg.c[]
 .. link:uio_read.c[]
 .. link:rand_check.c[]
+.. link:rdtsc.c[]
 . Module tests
 .. link:anonymous_inode.c[]
 .. link:poll.c[]

kernel_module/user/rdtsc.c

@@ -0,0 +1,26 @@
+/*
+Only works in x86_64.
+
+- https://en.wikipedia.org/wiki/Time_Stamp_Counter
+- https://stackoverflow.com/questions/9887839/clock-cycle-count-wth-gcc/9887979
+*/
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if defined(__i386__) || defined(__x86_64__)
+#include <x86intrin.h>
+#endif
+
+int main(void) {
+	uintmax_t val;
+#if defined(__i386__) || defined(__x86_64__)
+	/* https://stackoverflow.com/questions/9887839/clock-cycle-count-wth-gcc/9887979 */
+	val = __rdtsc();
+#else
+	val = 0;
+#endif
+	printf("%jx\n", val);
+	return EXIT_SUCCESS;
+}