Using Libraries

Like in many other languages, importing or including libraries are also possible in ASM. We will include the asm_io.inc as an example here. The required files can be found in the Resources section.

ASM Code

The following ASM code includes the asm_io.inc library and uses the dump_regs function defined in it.

dumpregs.asm

%include "asm_io.inc"

segment .text
    global asm_main

asm_main:
    enter 0, 0
    pusha        ; push registers on stack

    dump_regs 0     ; print register contents (in hexadecimal)

    popa          ; get the registers back from the stack

    mov eax, 0    ; return 0 to the C programm
    leave
    ret

Compilation

We first need to compile asm_io.asm and acquire asm_io.o here. Note that the -d ELF_TYPE tells the ASM code, that we are compiling for a Linux system. Read asm_io.asm for how to compile for other systems.

$ nasm -f elf -d ELF_TYPE asm_io.asm

Thenafter we can compile the executable with the following command:

$ nasm -f elf dumpregs.asm
$ gcc -m32 -o dumpregs driver.o dumpregs.o asm_io.o  

Execution

This program will show the registry contents on the console. Here is a sample output:

$ ./dumpregs
Register Dump # 0
EAX = 00000001 EBX = F7723000 ECX = FFD49F30 EDX = FFD49F54
ESI = 00000000 EDI = 00000000 EBP = FFD49EF8 ESP = FFD49ED8
EIP = 08048492 FLAGS = 0286       SF       PF