The document provides a basic guide to reverse engineering Linux x86 shellcode. It summarizes reversing two sample shellcodes: 1) A simple program that reads the /etc/passwd file by executing the cat command. By examining registers, it is determined the shellcode executes execve to read the file. 2) An XOR encrypted shellcode that decrypts itself before launching a ksh shell with root privileges using the setreuid system call. Breakpoints are used to stop and disassemble the shellcode at key points to understand its functionality.