Read a string and display first 5 characters in MIPS-CodePudding

I am trying to read a user input string and display the first 5 characters. I am able to get and print the string back, but I get Memory Address out of bounds most possibly in line move $a0,$t8 because my assignment to lb $t8 is wrong. I can not make this work.

#data segment
.data
    buffer: .space 20       #allocate space for 20 bytes=characters

#text segment
.text
    .globl __start 

#program start
__start:

    #get user input
    li $v0,8
    #load byte space
    la $a0,buffer
    #tell the system the max length
    li $a1,20
    move $t1,$a0
    syscall

    #display the input
    li $v0,4
    syscall

    #print 5 first characters
    li $t6,5

loop:   lb $t8,($t1)

    li $v0,4
    la $a0,buffer
    move $a0,$t8
    syscall 

    add $t1,1
    
    #1 less letter to print
    sub $t6,1

    #have we printed all 5
    bne $t6,0,loop

Does t1 not have the byte of the first string?

All help and/or any general tips outside of this problem is appreciated.

CodePudding user response：

There is no possibility that a move instruction causes a memory out of bounds exception. Only load and store instructions can cause that.

You are using syscall #4 to print a single byte, so the syscall attempts to dereference the byte provided in $a0 as a pointer, and as a mismatch, that's going to fault.

lb $t8,($t1)

li $v0,4
la $a0,buffer # putting buffer address in $a0
move $a0,$t8  # overwriting the buffer address with byte value in $t8
syscall