Create a week04 subdirectory in your weeklylab subdirectory and copy over some files:

    cd cs31/weeklylab		
    pwd
    mkdir week04
    ls
    cd week04
    pwd
    cp ~newhall/public/cs31/week04/* .
    ls
    Makefile simpleops.c

Week 4 lab goals:

1. Condition Code and ALU Lab
2. Some practice with IA32 assembly code, gcc, objdump
3. Learn gdb (and ddd) disassemble, ni, si, register contents
4. Disassemble a computer and see what parts you can identify.

Let's try out gcc to build IA32 assembly files and .o files and look at the results.

Open up simpleops.c in vim.

We are going to look at how to use gcc to create an assembly version of this file, and how to create a object .o file, and how to examine its contents. We are also going to look at how to used gdb to see the assembly code and to step through the execution of individual instructions.

If you open up the Makefile you can see the rules for building .s, .o and executable files from simpleops.c. We will be compiling the 32-bit version of instructions, so we will use the -m32 flag, and we are using version 4.4 of gcc (version 4.4 generates easier to read IA32 code):

gcc-4.4 -m32 -S simpleops.c   # just runs the assembler to create a .s text file
gcc-4.4 -m32 -c simpleops.s   # compiles to a relocatable object binary file (.o) 
gcc-4.4 -m32 -o simpleops simpleops.o  # creates a 32-bit executable file

To see the machine code and assembly code mappings in the .o file:

objdump -d simpleops.o

You can compare this to the assembly file:

cat simpleops.s

Next, let's try disassembling code using gdb. With gdb we can execute individual IA32 instructions, examine register values, and disassemble functions. Do a 'make clean' then a 'make' to rebuild an IA32 version of the simpleops executable file.

gdb simipleops
(gdb) break main
(gdb) run

In gdb you can disassemble code using the disass command:

(gdb) disass main

You can set a break point at a specific instruction:

(gdb) break *0x080483c1   # set breakpoint at specified address 
(gdb) cont
(gdb) disass 

And you can step or next at the instruction level using ni or si (si steps into function calls, ni skips over them):

(gdb) ni	  # execute the next instruction then gdb gets control again 
(gdb) ni
(gdb) ni
(gdb) ni
(gdb) ni
(gdb) disass

You can print out the values of individual registers like this:

(gdb) print $eax

You can also view all register values:

(gdb) info registers

You can also use the display command to automatically display values each time a breakpoint is reached:

(gdb) display $eax
(gdb) display $edx

We are going to try running this in ddd instead of gdb, because ddd has a nicer interface for viewing assembly, registers, and stepping through program execution:

ddd simpleops

The gdb prompt is in the bottom window. There are also menu options and buttons for gdb commands, but I find using the gdb prompt at the bottom easier to use.

You can view the assembly code by selecting the View->Machine Code Window menu option. You will want to resize this part to make it larger.

You can view the register values as the program runs (choose Status->Registers to open the register window).

See my GDB Guide for more information about using gdb and ddd. (see the "using gdb to debug assembly code and examine memory and register values" section).

Also see figure 3.30 on p.255 of the textbook.

Log out, and we are going to X. You have been randomly assigned to one of four groups. Each group is assigned a computer that you can take apart. The goal is to find as many parts of a computer as you can. We have tools available to remove parts from your computer, and here are a few links that may be helpful:

• Tour inside your PC
• Internal Computer hardware
• Video of inside a PC
• How PC's work

Try to identify some of the following:

• the processor
• RAM memory card(s)
• the backplane
• the chipset, PCI and Memory buses
• expansion slots
• the hard drive (what's inside?)
• the network interface card (NIC)
• the graphics card
• where do different ports go?
• ... then see what else you can find

Before leaving lab, please clean-up all spare parts, screws, etc. that you have removed by puting them in the boxes. You do not need to put the cases in the boxes, just all loose parts. CPU thermal glue is toxic, so just to be extra safe I'd recommend washing your hands after lab today.