MIPS: Fetch Address Not Aligned on Word Boundary

1
votes

I am getting the following error on my last line of code:

line 14: Runtime exception at 0x00400020: fetch address not aligned on word boundary 0x1000066a

I do not understand why I am getting this error since the word should be aligned perfectly at the address 0x10000004 (Since the global pointer is set to 0x10008000) so $s1 should be set to the value 0x0001.

.data   0x10000000
a:      .word 5
one:    .word 1

.text 0x400000
main:   addi    $s2, $zero, 30
        addi    $s3, $zero, 75
        addi    $sp, $sp, -4
        addi    $t0, $zero, 7
        sw  $t0, 0($sp)
        lw  $s0, -0x8000($gp)
        add $s4, $s0, $s2
        add $s4, $s4, $s3
        lw  $s1, -0x7996($gp)

All help and input is greatly appreciated.

2
runtimemipsmips32

2 Answers

2
votes

0x8000 is not eight thousand, from which you would subtract 4 to get 7996 this is actually in hexadecimal "0x" so the numbers are as such:

0x7FF8 0x7FFC 0x8000 0x8004 0x8008 0x800C etc..

I am also assuming from what you have said that you are on mips-32

1
votes

You're thinking in decimal terms. 0x8000 - 0x7996 equals 0x66A, which isn't word-aligned. What you should've written is:

lw  $s1, -0x7FFC($gp)