assembler directives

Assembler Directives

Example program:

.data # DATA segmentcity: .asciiz “Seattle”

.align 2num: .word 2210, 2341, 26, 0x022ec, 0x11110087

.byte 65, 79, 253

.text # CODE segment

.globl main # declaring “main” as global

main: li $v0, 4 # syscall for print_stringla $a0, city # argument in $a0syscall

la $t0, num # get address of first number

lw $s0, 0($t0) # s0 = 2210 lw $s1, 4($t0) # s1 = 2341

add $s0, $s0, $s1 # s0 = 2210+2341li $v0, 1 # syscall for print_intmove $a0, $s0 # argument in $a0syscall

.end main

General format of MIPS programs

Xspim on our machines automatically loads some assembly code that takes care of calling “main”

Need to write code that looks roughly like the following:

.data # DATA segment

lab1: .byte ……… lab2: .asciiz …… # some static data

.float ………lab3: .double ……...

.text # CODE segment

.globl main # declaring “main” as global

main: <your part of the code>…...

.end main

If-then-else in MIPS

What does the following C code looks like in MIPS assembly language:

if (a < b) { a = a + 1; b = b - 1;}else { a = a * 2; b = b / 2;}

Assume $s0 contains a, and $s1 contains b.

If-then-else (cont.)

# if (a < b)slt $t0, $s0, $s1beq $t0, $zero, else_label

# a = a + 1, b = b - 1addi $s0, $s0, 1subi $s1, $s1, 1j end_label

# else a = a * 2, b = b / 2else_label:sll $s0, $s0, 1sra $s1, $s1, 1

# end of if-then-elseend:<statements following if-then-else>

From C Program to Machine Language

Stages in the transformation:

C program

Assembly Language program

Object : MachineLanguage Module

Library routinesMachine Lang

Executable (Machine Language)

Memory

Compiler

Assembler

Linker

Loader