MIPS assembler memory alignment issue (detailed code included)

Question

I am trying to store a integer that i am reading from the user into a array, however when i try to store it into my array my data becomes unaligned.

This first block of code is where i initialize all the data. (Under the 1. is where i am trying to store the integer )



'#Constants
P_INT        = 1      #Syscall to print integer(value)
P_STRING     = 4      #Syscall to print a string(addr)
P_CHAR       = 11     #Syscall to print a char(char)
R_INT        = 5      #Syscall to read a integer(none)
EXIT         = 10     #Exit program(none)

'#Data
        .data
newline:
        .asciiz "\n"        

'#Space for the bored.

 1. 
board_rep:
        .space     578

'#The current node to be read in
cur_node:
        .word      0 

'#Size of the bored
size:
        .space     4
'#Plus sign
plus:
        .asciiz "+"
'#dash
dash:
        .asciiz "-"

Right here is where it becomes unaligned (the sw right after 2.) . The strange thing is that i am doing the exact same thing later (in the third code block) except that i am storing it in the size array.



'#Grabs user input for the bored and stores it
get_board_rep: 


        li       $v0,R_INT     '#Read next node and store it    
        syscall 
2.
        sw       $v0,0($s1)

        addi     $s1,$s1,4    ' #Increment next node addr

        lw       $a0,0($s1)
        j        prnt_node

At the store word (under the 3. ) it stores the read in integer fine.



        la        $s0, size      ' #Store the variable addr's
        la        $s1, board_rep  

        li        $v0,R_INT      ' #Get user input(size of bored)
        syscall 
3.
        sw        $v0,0($s0)     ' #Store the size of bored


        jal       get_board_rep

I thought maybe the array was too large but i changed it to 4 (the same size that the other array that worked). But it still was unaligned.

Thanks in advance . This is a project and i know some people don't like helping with stuff like this. But i have done my homework and i cannot find a answer anywhere.

I figured it out, apparently the two space allocations needed to be right after one another. Otherwise it would unalign the data. I am not sure if this is exactly what is going on here but it fixed my problem. Seems a bit weird does anyone know if this is true for all MIPS programs? — TacticalMin
– TacticalMin, Commented Apr 29, 2012 at 3:50
Did you bring board_rep down to size, or carry size up to board_rep? — Musa
– Musa, Commented Apr 29, 2012 at 4:57

Musa · Accepted Answer · 2012-04-29 02:47:05Z

1

That doesn't look aligned to me, and if i'm wrong try explicitly aligning it anyway.

answered Apr 29, 2012 at 2:47

Musa

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2 Comments

TacticalMin Over a year ago

I did do a .align 2 in the code it is just not shown in any of these snippets.

Musa Over a year ago

Well if your having alignment issues, posting alignment code might be relevant

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