CS323 - Note 2 – Day 2 – 1/25/2006
First & Second Programs

Number Systems (review) See Handout for today.

 Decimal, binary, hexadecimal, octal
 Signed Integers 
 Signed magnitude
 One’s complement
 Two’s complement

Unix – demo if necessary: PuTTy and WinSCP

Steps in Assembly Programming - demo if necessary. (edit, assemble, link, run) – mp00

To edit, use : joe first.asm (or vi or emacs or WinSCP editor)

To assemble your program, give the following command:

nasm –f elf first.asm

If this command works correctly, you will simply get a new prompt and a file first.o will be created. Use the ls command to see that the file was created. Note ELF stands for Executable and Linkable Format.

To create an executable program, give the following command:

gcc first.o driver.c asm_io.o

If this command works correctly, you will simply get a new prompt and a file a.out will be created.

To run the program, give the command:

a.out

Look at an list file (use –l listing_file)

See page 21 in Carter for a detailed discussion of first.asm

Debugging

To debug use the commands(macros) given in Carter’s textbook:

dump_regs to dump/display the registers

dump_mem to dump/display sections of memory

dump_stack to dump/display the stack

Skeleton program

;
; file: skel.asm
; This file is a skeleton that can be used to start assembly programs.

%include "asm_io.inc"
segment .data
;
; initialized data is put in the data segment here
;


segment .bss
;
; uninitialized data is put in the bss segment
; block-started-by-symbol


segment .text
global asm_main
asm_main:
enter 0,0 ; setup routine
pusha

;
; code is put in the text segment. Do not modify the code before
; or after this comment.
;

popa
mov eax, 0 ; return back to C
leave
ret

Basic Concepts

 Assembly is NOT totally case insensitive, e.g. 
 Register names like EAX and eax are the same.
 Variable names like prompt and PROMPT are different.
 
 Assembly Program has three segments
 Stack, data, and code
 
 Pseudo Operations /Directives
  -directs assembler to do something, e.g.
 -- define constants
 -- define memory
 -- group memory into segments
 -- include files (possibly conditionally)
 
 Directives are not machine instructions
 
 %define BUFSIZE 10
 
 Pseudo operations DB, DW, DD, DQ, DT (see page 14 of Carter)
 Define variables with initial values
 Use resb, resw, resd, resq, rest to reserve values with NO initial values.
 
 Data types: byte, word, double word, quad word, ten bytes
 See page 14 and 15 in Carter text
 
 Registers – 16 bit 
  AX, BX, CX, DX, DS 
 Each one is a word, and has a high byte and a low byte
  AX: AH AL
 Registers – 32 bit : eax, ebx, ecx, edx, edi, esi
 AX is the lower half of EAX, AL is lower half of AX, AH is upper half of AX
  Same can be said for relationship between bx and ebx, cx and ecx, dx and edx

Examine mp10 – second assembler program

Nasm Documentation & Programming GroundRules

 
See S:\Academic\CSSE\CS\Cs323\Nasm\SampleNASM\nasmdoc.pdf
 
Programming Groundrules (http://www.uwplatt.edu/csse/Courses/CS323/asm-rules.html)