Complete Program

Here is the complete example program. The global symbols have been correctly declared. Study how each module uses the directives .text and .data to describe its sections. Each file describes what part of it is to go into the (one and only) text section of run-time memory and the (one and only) data section.

With a real OS, each source file is separately assembled into an object file which has a text section and a data section. The linker has the job of putting all the separate pieces together into the right sections of run-time memory. This is somewhat like putting together a jigsaw puzzle to form one picture from many pieces.

As you "Load" each file from the file menu, QtSpim will ensure that the text sections are placed into the single text section of (simulated) main storage and that the data sections are placed into the data section. In a real operating system, this is the job of the linker and loader.

# addthree.asm --- read in three integers and print their sum
#
# This program uses simple linkage.  
#
# Settings: Load delays  ON;  Branch delays ON
#           Trap file    ON;  Pseudoinstructions ON   
#

         .text
         .globl  main
main:
         jal     pread            # read first integer
         nop                      #  
         move    $s0,$v0          # save it in $s0

         jal     pread            # read second integer
         nop                      #  
         move    $s1,$v0          # save it in $s1

         jal     pread            # read third integer
         nop                      #  
         move    $s2,$v0          # save it in $s2
         
         addu    $s0,$s0,$s1      # compute the sum
         addu    $s3,$s0,$s2      # result in $s3
 
         li      $v0,4            # print a heading
         la      $a0,heading         
         syscall

         move    $a0,$s3          # move sum into parameter
         li      $v0,1            # print the sum
         syscall
        
         li      $v0,10           # exit
         syscall
          
         .data
heading:
         .asciiz "The sum is: "

        
 # pread.asm -- prompt for and read an integer
#
# on entry:
#    $ra -- return address
#
# on exit:
#    $v0 -- the integer

         .text
         .globl  pread
pread:   
         la    $a0,prompt        # print string
         li    $v0,4             # service 4
         syscall
        
         li    $v0,5             # read int into $v0
         syscall                 # service 5
        
         jr    $ra               # return
         nop                     #  
        
         .data
prompt:
         .asciiz "Enter an integer: "

Here is a picture of the console window after the program has run:

Answer:

Complete Program

QUESTION 15: