; Program to print the time-stamp counter on x64 Linux
; Author: illustrissimus

; To build and run:
; nasm -f elf64 -o rdtsc.o rdtsc.asm
; ld -o rdtsc rdtsc.o; strip -s rdtsc
; ./rdtsc |od -An -t x4 |tr -d ' '

; To inspect:
; objdump -M intel -d rdtsc

; To check if the instruction is supported:
; grep tsc /proc/cpuinfo

default rel

global _start

section .bss
tscv_low: resb 4
tscv_high: resb 4

section .text
_start:
; read the counter
        rdtsc
        mov     dword [tscv_low], eax
        mov     dword [tscv_high], edx

; write to stdout
        mov     rax, 1 ; write
        mov     rdi, 1 ; stdout
        lea     rsi, [tscv_high]
        mov     rdx, 4 ; number of octets to print
        syscall
        mov     rax, 1 ; write
        mov     rdi, 1 ; stdout
        lea     rsi, [tscv_low]
        mov     rdx, 4 ; number of octets to print
        syscall

; exit the program
        mov     rax, 60 ; exit
        mov     rdi, 0 ; exit code
        syscall