These exercises should help you exercise your assembly reading skills;
the best way to is to write simple snippets of code yourself.

Note: make sure you write and build assembly code for your actual platform.
      For 32bit Linux, use "nasm -f elf prog.s" and use 32bit mnemonics,
      for 64bit, "nasm -f elf64 prog.s", and use the proper calling
      conventions for system calls (these are very different between
      the systems, see syscall.txt).  

HINT: When in doubt about system calls and their arguments, use the 
      "strace" command. It is most useful in the form "strace <command> 2>&1 | less",
      because by default it sends its output to standard error stream 
      (file descriptor 2) rather than to standard output (fd 1); 2>&1 
      duplicates fd 2 to fd 1. 

0. Warm-up. What does this do? 

          call _foo
_foo:     pop  edx 
	  
   Can you explain the '00 00 00 00' in the binary expression of the call 
   instructions?

   For example, what would the following code return and why? (note, you
will need to pick up its return code with 'echo $?'):

;---------- call-pop.s (download from cs258/examples/) --------
BITS 32
section  .text
global   _start
_start:
	  call  _bar
_bar:	  pop   ecx
          call  _foo
_foo:     pop   ebx
          sub   ebx, ecx
          mov   eax, 1
          int   80h
;---------------------------------------------------------------


1. Write a program than prints the first 100 bytes of a file (say, /etc/issue)
   to standard output.


2. Write a program that prints the contents of a file (say, /etc/passwd)
   to standard output.


3. Write a minimal version of 'ls' that prints the names of all files in the 
   current directory (same as the 'ls' command withough any arguments).


4. Write a minimal version of 'ps' that prints the PIDs and names of all
   processes running on the system. 


When in doubt, use single-stepping, and "info reg" in GDB to see the effect
of an instruction on registers.