How to get time in milliseconds in assembly?

Question

I was able to get it in seconds, but how to get the value of milliseconds? I am trying with the gettimeofday system call:

sys_gettimeofday_ms:
enter   $0, $0
pushq   $0
pushq   $2
leaq    -16(%rbp), %rdi
mov     $96, %rax
syscall

movq    -16(%rbp), %rax

leave
ret

Answer 1

This might work (untested), targeting x86_64 Linux.

sys_gettimeofday_ms:
    mov rax, 96
    lea rdi, [rsp - 16]
    xor esi, esi
    syscall
    mov ecx, 1000
    mov rax, [rdi + 8]
    xor edx, edx
    div rcx
    mov rdx, [rdi]
    imul rdx, rcx
    add rax, rdx
    ret