NasmLessons/05-userinput.asm

;;; Required packages: nasm, ld
;;; compile commands:
;;;     nasm -f elf 05-userinput.asm -o bin/05-userinput.o
;;;     ld -m elf_i386 -s -o bin/05-userinput bin/05-userinput.o

%define SYSCALL_EXIT 1 ; system call sys_exit
%define SYSCALL_WRITE 4 ; system call sys_write
%define SYSCALL_READ 3
%define STDIN 0 ; file descriptor stdin 
%define STDOUT 1 ; file descriptor stdout 

%define NAME_BUFFER_LEN 256

section .data 
    question db "What is your name? ", 0xa
    questionLen equ $ - question

    prompt db "> "
    promptLen equ $ - prompt

    greetings db "Hello, "
    greetingsLen equ $ - greetings

section .bss 
    name resb NAME_BUFFER_LEN ; resb -> Reserve 16 bytes

section .text 
    global _start 

_start:
    call printQuestionAndPrompt
    call scanName
    call printGreetings

    ; exit code 
    mov eax, SYSCALL_EXIT ; 
    mov ebx, 0 ; 0 - error code
    int 0x80 ; processor interruption to run syscall 

    ret

scanName:
    mov eax, SYSCALL_READ
    mov ebx, STDIN
    mov ecx, name 
    mov edx, NAME_BUFFER_LEN
    int 0x80
    
    ret

printGreetings:
    mov eax, SYSCALL_WRITE 
    mov ebx, STDOUT 
    mov ecx, greetings ; text 
    mov edx, greetingsLen ; text size
    int 0x80 ; processor interruption to run syscall

    mov eax, SYSCALL_WRITE 
    mov ebx, STDOUT 
    mov ecx, name ; text 
    mov edx, NAME_BUFFER_LEN ; text size (16 bytes reserved)
    int 0x80 ; processor interruption to run syscall

    ; name ends with \n

    ret

printQuestionAndPrompt:
    mov eax, SYSCALL_WRITE 
    mov ebx, STDOUT 
    mov ecx, question ; text 
    mov edx, questionLen ; text size
    int 0x80 ; processor interruption to run syscall

    mov eax, SYSCALL_WRITE 
    mov ebx, STDOUT 
    mov ecx, prompt ; text 
    mov edx, promptLen ; text size
    int 0x80 ; processor interruption to run syscall 

    ret