%macro sysdef 2
  %define sys_%1    %2
%endmacro
sysdef write,       1

%macro prolog 1
  push rbp
  mov rbp, rsp
  sub rsp, %1
%endmacro

%macro epilog 1
  add rsp, %1
  pop rbp
%endmacro

%macro xlea 2
  lea %1, [rel %2]
%endmacro

%macro inv 1-7 0,0,0,0,0,0
  mov r9,%7
  mov r8,%6
  mov r10,%5
  mov rdx,%4
  mov rsi,%3
  mov rdi,%2
  mov rax,sys_%1
  syscall
%endmacro

section .rodata
sz1     db "Goodbye, World!",0xa,0

section .bss
sz2     resq 1

section .text
  strlcpy:
    prolog 0x38
    %define dest  rbp-0x18
    %define src   rbp-0x10
    %define n     rbp-0x8

    mov qword [rbp-0x28], rdi
    mov qword [rbp-0x30], rsi
    mov qword [rbp-0x38], rdx
    mov rax, qword [rbp-0x28]
    mov qword [dest], rax
    mov rax, qword [rbp-0x30]
    mov qword [src], rax
    mov rax, qword [rbp-0x38]
    mov qword [n], rax
    cmp qword [n], 0
    je _stlc_done
    _stlc_doloop:
      dec qword [n]
      cmp qword [n], 0
      je _stlc_done
      mov rbx, qword [src]
      lea rax, [rbx+1]
      mov qword [src], rax
      mov rax, qword [dest]
      lea rcx, [rax+1]
      mov qword [dest], rcx
      movzx ebx, byte [rbx]
      mov byte [rax], bl
      movzx eax, byte [rax]
      test al, al
      je _stlc_done
      jmp _stlc_doloop
    _stlc_done:
    epilog 0x38
    ret

  strlen:
    prolog 0x10
    %define s rbp-0x8

    mov qword [rbp-0x10], rdi
    mov rax, qword [rbp-0x10]
    mov qword [s], rax
    mov rsi, qword [s]
    xor rcx, rcx
    _stl_count:
      cmp byte [rsi+rcx], 0
      je _stl_exit
      inc rcx
      jne _stl_count
    _stl_exit:
      mov rax, rcx
    epilog 0x10
    ret

    global main
    main:
      prolog 0x20
      %define tmp rbp-0x20
      xlea rbx, sz1
      mov qword [tmp], rbx
      mov rdi, qword [tmp]
      call strlen
      mov rcx, rax
      push rcx
      mov rdx, rcx
      xlea rsi, sz1
      xlea rdi, sz2
      call strlcpy
      xlea rbx, sz2
      pop rcx
      inv write, 1, rbx, rcx
      inv exit, 0
      epilog 0x20
      ret