Creating a program

Question 1

What are the sections of a program?

Answer 1

A text section, data section,

Question 2

What is the file extension for a assembly program in Linux system?

Answer 2

.asm

Question 3

How do you create a text section.

Answer 3

In the editor type:

“section .text”

Question 4

How do you create a data section?

Answer 4

“section .data”

Question 5

What goes inside the data section?

Answer 5

The message the program needs to print placed inside of the data section.
Ex:
section .data
message: db “Hello World!”

Question 6

What is the linker of a program?

Answer 6

It is the entry point of a program.
Ex.
global _start

section .text
_start:

Question 7

How do you invoke a system call?

Answer 7

A user space program calls a system call by invoking it with a generated interrupt such as “int 0x80”, “SYSENTER” or VDSO.

Question 8

What are system calls?

Answer 8

Provides a interface for user space programs to request the kernel to execute tasks.

Question 9

Where are system calls located?

Answer 9

/usr/include/1386-linux-gnu/asm/unistd_32.h

Question 10

What command can be used to count a string in an asm program?

Answer 10

mlen equ $-message

Question 11

What system call can be used to write a program to screen?

Answer 11

_write identified in a program by the number 4

Question 12

What system call will exit a program?

Answer 12

_exit closes a program with the status code given by the programmer.

Question 13

Where in the program is the system call located?

Answer 13

It is located in the text section of the program. Below is code to print the message on the screen.
Ex:
_start:
              mov eax, 0x4
               mov ebx, 0x1
               mov ecx, message
               mov edx, mlen
               int 0x80 (invokes syscall)