UNIX programming course

Nibbles assignment

In the assignments, you should implement a nibbles game in IA-32 assembly. The requirements for the lab can be found here: nibbles.pdf. For the assignment, a library of helper functions (to set chars on the screen etc) have been implemented. Download that here: helpers.tar.gz

The lecture notes for the assembly part is available below:

Intel IA-32 assembly (two lectures). For the UNIX Programming course at BTH:

Download PDF for printing (6 pages per page) or for viewing online

Tournament

The course includes a competition, producing the smallest implementation of a nibbles game. More information can be found on the Nibbles Assembly tournament page.

X86 reference

An X86 instruction set reference (AT&T-style) can be found here: x86ref.pdf.

Short assembly programs

I've collected a number of short x86/IA-32 assembly programs on theIA-32 assembly examples page.

GDB

I use a few assembly-related macros for GDB. My ~/.gdbinitcontains these.

The supplied Makefile contains a rule to compile code to run under GDB. With this, it is possible to use the normal debugging utils in GDB. Some hints:

• Registers in GDB require a "$"-sign, i.e. print $eax prints the value of the %eax register.
• ncurses-applications (like nibbles) cannot run directly within the debugger (since they change the position of the cursor). Instead, start the game as usual and attch to it from GDB. This is done by:

attach PID

where PID is the process ID of the nibbles game.

• You can examine the top of the stack (first 8 words) by doing x/8x $esp or using the macros supplied on gdbinit.html.
• You can disassemble the code at the current position by doing x/8i $pc (this gives better results then the disassemble command imo)

Running a program in GDB

Start gdb with the program-name as argument, i.e. gdb prg. In Emacs you can start GDB by doing M-x gdb and then entering the program name.

A typical session can be seen below:

...
(gdb) b _start
Breakpoint 1 at 0x8048196: file prg.S, line 13.
(gdb) run
Starting program: /home/ska/tmp/prg

Breakpoint 1, _start () at prg.S:13

13             movl  $1, %eax
Current language:  auto; currently asm
(gdb) list
8              movl  $3, %ebx        # %ebx = 3
9       out:
10             ret
11      .globl _start
12      _start:
13             movl  $1, %eax
14             call  if_stmt
15             ## %ebx will be 3 here
16             pushl %ebx
17             call  exit
(gdb) s
14             call  if_stmt
(gdb) p $eax
$1 = 0x1
(gdb)

You can find a quick reference to GDB at www.refcards.com.

Misc tools

objdump

[ska@ipdska tmp]$ objdump -d prg.o

prg.o:     file format elf32-i386

Disassembly of section .text:

00000000 <_start>:
   0:   b8 01 00 00 00          mov    $0x1,%eax
   5:   bb 02 00 00 00          mov    $0x2,%ebx
   a:   cd 80                   int    $0x80

readelf

#!/bin/sh

while [ $# -ne 0 ]; do
    echo -n "$1: "
    readelf -S $1 | egrep " .text| .data" | sed 's/ 00/ 0x0/g' | mawk 'BEGIN{sum=0;}{sum = sum + $7;}END{print sum}'
    shift
done

Pass the ELF-files to check to the script.

Links

A very nice book about IA-32 assembly for Linux/UNIX which is written in AT&T-syntax is "Professional Assembly Language" by Richard Blum. It can be found at adlibris.

PC Assembly Language - A very nice book about IA-32 assembly by Dr. Paul Carter. Uses the Intel syntax, and has (too my taste) slightly too long examples, but still is a very good reference to IA-32 assembly.

Programming from the ground up - Introduction to assembly language in book-form by Jonathan Bartlett. Uses AT&T-style assembly and focuses on assembly in UNIX systems.

developer.intel.com/.../245470.htm - The IA-32 Software Developer's Manual (volume 1-3). A couple of thousand pages about everything around x86 processors. Volume 2 contains the instruction set reference. Uses Intel-syntax.

linuxassembly.org - A collection of much information about programming assembly in UNIX-systems.

www.cs.colorado.edu/.../nasmdoca.html - The NASM manual (instruction set reference). Good reference, uses intel-syntax.

Intel Assembler 80x86 CodeTable - Intel assembly reference page, intel-syntax, but otherwise very nice.

Feedback?

Direct feedback to ska[at]bth[dot]se (change the obvious!)