1)Create an object file

as --32 program.asm -o program.o
//this code invokes the "as" assembler and creates an object file as a 32 bit code 
//"as" assembler is preinstalled in linux

2)Linking

ld -m elf_i386 program.o -o program  
//this code invokes the linker and links the object files in an ELF format producing an executable code as output

3)Using the gdb

a)gdb program -q

b)disassemble _start:This code outputs all the instructions under start label,you can disassemble other labels as well

c)break "label" :sets break point in the mentioned label(use break _start in most cases)

d)run:starts the program

e)info variables:displays the address and name of each variables used

f)info registers:displays contents in each register

g)display :this command is used to display contents of a register or memory throughout the program

h)p : can be used to print the contents inside a register once

i)x : can be used to print the contents inside a memory location at once

j) /x : suffixed to display,p,x can be used to represent contents in hexadecimal format

k) /d : suffixed to display,p,x can be used to represent contents in decimal format

l) /t : suffixed to display,p,x can be used to represent contents in binary format

m) /i : suffixed to display,p,x can be used to represent contents in instruction format(used to display instructions in eip register)

n) note that registers need to be prefixed with a "$" symbol! eg: p /x $eax(display contents in EAX register in hex )

o) note that if name of variable is used to access memory then "&" should be used in prefix!

4)Tip

Use display $eflags before running any program to view how instructions affect the flags in the system