Linux64io

A I/O helper library for NASM assembly programs on Linux and WSL.

It does direct Syscalls and readable functions and macros. The main requirements are:

• NASM
• GNU Binutils
• Linux or WSL

Installation for the binutils and NASM

You can run in the terminal the following command:

sudo apt install nasm binutils

Usage

In a assembly project (.asm), you put linux64io.inc in the same folder and in the assembly code that you desire to use the package just write the following snippet of code

%include "linux64io.inc"

Macros

The library got the following macros, doesn't require complex setup, but doesn't allow a lot of control.

Macro	Example	Description
PRINT_STR	PRINT_STR msg, msg_len	Print a string defined in .data
PRINT_INT	PRINT_INT r12	Print an integer followed by a newline
READ_INT	READ_INT r12	Read an integer from stdin into a register

Functions

This allows more control, calling them directly allows you to use pointers and the bytes written.

Function	Input	Output	Description
print_str	rsi = pointer, rdx = length	rax = bytes written	Print a string
print_int	rax = integer	—	Print an integer with newline
print_newline	—	—	Print a newline character
read_int	—	rax = integer	Read an integer from stdin
read_str	rsi = buffer, rdx = max length	rax = bytes read	Read a raw string from stdin

Example Program

%include "linux64io.inc"

section .data
    msg     db "Enter a number: "
    msg_len equ $ - msg
    res_msg db "Doubled: "
    res_len equ $ - res_msg

section .text
    global _start

_start:
    PRINT_STR msg, msg_len
    READ_INT r12            ; r12 = user input

    imul r12, r12, 2        ; double it

    PRINT_STR res_msg, res_len
    PRINT_INT r12

    mov rax, 60             ; exit
    xor rdi, rdi
    syscall

Compile & Run

Test code still in progress to include

# Single file
nasm -f elf64 your_program.asm -o your_program.o
ld your_program.o -o your_program
./your_program

# Using the Makefile (builds suma, factorial, primo)
make
./sumNum
./factorial
./primeNum

# Clean up object files and binaries
make clean

Register Safety

Linux syscalls internally clobber rcx and r11. Use r12–r15 to safely hold values across function calls — the library never touches them.

Function	Clobbers
print_str	rax, rdi
print_int	rax, rdx, rdi, rsi, rbx, r9, r10
print_newline	rax, rdi, rsi, rdx
read_int	rax, rcx, rdx, rdi, rsi
read_str	rax, rdi