Mips Procedure: Infinite for loop and Exception occurred at PC - exception

Question

Seeing the topics on the site, however I was not able to solve my problem. I noticed that the code inside the procedure falls into an infinite for and in QTSpim I saw that the registers involved are $s0, $s1, $t2, and $t4.
After a few cycles then the message Exception occurred at PC then expection 7 Bad data address.
Here is the code, I can not figure out where mistake, I tried to write it without procedure and it works perfectly.
.data
string: .asciiz "Hello Simon"
string2: .asciiz ""
.text
.globl main
Delete_space:
addi $sp, $sp, -16
sw $s0, 0($sp)
sw $s1, 4($sp)
add $t8, $a0, $zero
lenght_string:
lb $t0, 0($t8)
beqz $t0, for #t8 contain the lenght of string
add $t8, 1
j lenght_string
for:
add $s0, $zero, $zero #i=0
add $s1, $zero, $zero #j=0
condition:
slt $t1, $s0, $t8 #i< lenght_string
beq $t1, $zero, endfor
consequence:
add $t2, $t8, $s0
lb $t3, 0($t2)
bne $t3, ' ', op1
beq $t3, ' ', else
addi $s0, $s0, 1
addi $s1, $s1, 1
j condition
op1:
add $t4, $a1, $s1
sb $t3, 0($t4)
addi $s0, $s0, 1
addi $s1, $s1, 1
j condition
else:
sub $s1, $s1, 1
addi $s0, $s0, 1
addi $s1, $s1, 1
j condition
endfor:
#end
lw $s1, 4($sp)
lw $s0, 0($sp)
addi $sp, $sp, 16
jr $ra
main:
la $a0, string
la $a1, string2
jal Delete_space
la $a0, string2
li $v0, 4
syscall
li $v0, 10
syscall

Answer 1

I think you're trying to copy characters from one string to the other, skipping spaces. (Maybe that's not what you're trying to do - unfortunately, I don't have time to trace the code in detail.) I think the problem is that you're copying from your source string into a data area that doesn't belong to you.
Strings aren't handled the same in Assembly as they are in a high-level language. They're nothing but a sequence of bytes - there is no concept of a String that automatically expands to contain what you put in it. And there's no concept of bounds checking.
Look at these string declarations:
.data
string: .asciiz "Hello Simon"
string2: .asciiz ""
What you've done is assigned string to a memory address containing the byte value 'H'. The subsequent memory locations contain 'e', 'l', 'l', 'o', ' ', 'S', 'i', 'm', 'o', 'n', '\0'.
Then, you've assigned string2 to a memory address containing the byte value '\0' (a null terminator).
If you write a byte to the memory address pointed to by string2, it would replace the null terminator. (You would already be in trouble at this point, because the syscall wouldn't know where your string ends.) If you then write another byte to the memory address pointed to by string2 + 1, you are now writing to memory that you didn't allocate to string2. It might belong to some other variable that's being stored - in which case, you just overwrite what was there before. That's a "buffer overflow", and it's how poorly-written programs such as Internet Explorer get exploited by hackers.
If I'm interpreting the purpose of your program correctly, you need to create a buffer for your output that's big enough to hold it. Something like this would work, assuming your output will never be longer than your input:
.data
string: .asciiz "Hello Simon"
string2: .asciiz "xxxxxxxxxxx"