## LSU EE 3755 -- Fall 2001 -- Computer Organization
#
## Note Set 11 -- Object Files and System Calls

## Under Construction
# Time-stamp: <7 November 2001, 17:47:15 CST, koppel@sol>
#
# Coming Soon (Maybe)
#
# System Calls
# Program Preparations Steps

These notes are outdated. 
The lectures page contains links to the latest versions of these notes.

## Contents
#

## References
#
# :PH:  Patterson & Hennessy, "Computer Organization & Design"
# :Mv1: MIPS Technologies, "MIPS32 Architecture for Programmers Vol I: Intro"
# :Mv2: MIPS Technologies, "MIPS32 Architecture for Programmers Vol II: Instr"


################################################################################
## Structure of SPIM Assembly Language File

# Simplified form of a real assembly language program.

 ## What an Assembler Does
#
# Creates an object file consisting of a number of sections
# Some sections are:
#
#  :Def: Section Header
#  A directory to the other sections.
#  Used by programs that read the object file.
#
#  :Def: Text Segment
#  The program. (Encoded instructions, we know about these.)
#  Stuff that gets loaded into memory before the program is run.
#
#  :Def: Data Segment
#  Encoded data. (Haven't seen this yet. Not much to it.)
#  Stuff that gets loaded into memory before the program is run.
#
#  :Def: Symbol Table
#  A list of symbols used in the assembler file.
#  These are used for linking object files together.
#
#  :Def: Relocation Information
#  Places in object file that refer to as yet undetermined memory locations.
#
#
 ## Relevant Sections for this Class
#
# Text
# Data


 ## Assembly Program Elements
#
# Instructions
#   These should be familiar
#
# Line Labels
#   These should be familiar
#
# Assembler Directives
#   Tell the assembler how to interpret what follows.


 ## Assembler Directives
#
# These are a subset of directives recognized by real assemblers.
#
        .text
#       Tells the assembler that what follows is program code.
#       The assembler encodes instructions and places them in the text segment.
#
        .data
#       Tells the assembler that what follows is data.
#       The encoded data is placed in the data segment.
#
        .globl FOOBAR
#       Tells assembler that other files may refer to symbol FOOBAR.
#       In real assemblers, this is needed so files can be linked together.
#       In SPIM use globl to SPIM can "see" __start, the entry point.
#
        .byte 1, 2, 3, ...
        .half 1, 2, 3, ...
        .word 1, 2, 3, ...
        .float 1.1, 2.2, 3.3, ...
        .double 1.1, 2.2, 3.3, ...
#       Tell the assembler to include the specified data.  The
#       specified data is converted into the indicated format:
#       .word, 32-bit integers;  .byte, 8-bit integers.
#
        .ascii  "Hello class. I am an ascii string. I'm not terminated."
        .asciiz "Hello class. I am an ascii string, null-terminated as in C."
#       Tell the assembler to include the specified data.  Each
#       character takes up one byte of memory.  For .asciiz a zero
#       is written after the last character (which is the way it's done
#       in c).


# :Example:
#
# A short assembly language program illustrating: .data, .text, .asciiz, .globl

        .data
happy_msg:
        .asciiz "Hello, class!!"

        .text
        .globl __start
__start:
        la $a0, happy_msg
        addi $v0, 4
        syscall
        addi $v0, 10
        syscall
####



        .text
        .globl __start
__start:
        li $a0, 0x12345678
        addi $t0, $0, 7
        add $t1, $a0, $0
        add $v0, $0, $0
LOOP:
        andi $t2, $t1, 0xf
        sll $v0, $v0, 4
        srl $t1, $t1, 4
        or  $v0, $v0, $t2
        bne $t0, $0 LOOP
        addi $t0, $t0, -1




## Under Construction Below, an above too.


# Prep steps: code, compile, assemble, link, load
# HLL to Assembly to Machine

# loads and stores. Ex: array traversal.

# Working with characters.