bits 64

    SECTION .data
; empty
    echobuf db 1024

    SECTION .text

global _start
_start:
    ;int3

read:
    ; sys_read(stdin, buf, buflen)
    mov rax,0
    mov rdi,0           ; arg1: fd (0 = stdin)
    lea rsi,[echobuf]   ; arg2: buffer
    mov rdx,1024        ; arg3: buflen
    syscall

    test rax, rax
    jz exit

    ; sys_write(stdout, buf, buflen)
    mov     rdx,rax         ; arg3: buflen
    mov     rax,1           ; system call number (1 = sys_write)
    mov     rdi,1           ; arg1: fd (1 = stdout)
    lea     rsi,[echobuf]   ; arg2: buffer
    syscall
    jmp read

exit:
    ; sys_exit(42)
    mov     rax,60  ; system call number (sys_exit)
    mov     rdi,0   ; system call return value
    syscall

    times 64 nop