冒泡排序 MIPS 中的打印功能出错？

Question

很抱歉，这是一段很长的代码，但是您在其中看到任何明显的语法错误吗？编译器告诉我有一个运行时执行错误：0x00400008 处的运行时异常：地址超出范围 0x00000000。如果可以的话请帮忙！

        .data
save:   .word 1,2,4,2,5,6
size:   .word 6
        .text

    la $s6, save #load address of array
    la $t5, size #load address of size 
    lw $t5, 0($t5) #load array size
    sw $t0, 0($s6) #save the first element of the array
    sw $t1, 4($s6) #save the second element of the array
    j sort #call sort function

swap:   sll $t1, $a1, 2 #shift bits by 2 
        add $t1, $a1, $t1 #set $t1 address to v[k]
    lw $t0, 0($t1) #load v[k] into t1 <- ERROR
    lw $t2, 4($t1) #load v[k+1] into t1 
    sw $t2, 0($t1) #swap addresses
    sw $t0, 4($t1) #swap addresses
    jr $ra #return 

sort:   addi $sp, $sp, -20 #make enough room on the stack for five registers
    sw $ra, 16($sp) #save the return address on the stack
    sw $s3, 12($sp) #save $s3 on the stack
    sw $s2, 8($sp) #save Ss2 on the stack
    sw $s1, 4($sp) #save $s1 on the stack
    sw $s0, 0($sp) #save $s0 on the stack

    move $s2, $a0 #copy the parameter $a0 into $s2 (save $a0) 
    move $s3, $a1 #copy the parameter $a1 into $s3 (save $a1)
    move $s0, $zero #start of for loop, i = 0
for1tst: slt $t0, $s0, $s3 #$t0 = 0 if $s0 S $s3 (i S n)
    beq $t0, $zero, exit1 #go to exit1 if $s0 S $s3 (i S n)
    addi $s1, $s0, -1 #j - i - 1
for2tst: slti $t0, $s1, 0 #$t0 = 1 if $s1 < 0 (j < 0) 
    bne $t0, $zero, exit2 #$t0 = 1 if $s1 < 0 (j < 0)
    sll $t1, $s1, 2 #$t1 = j * 4 (shift by 2 bits)
    add $t2, $s2, $t1 #$t2 = v + (j*4) 
    lw $t3, 0($t2) #$t3 = v[j]
    lw $t4, 4($t2) #$t4 = v[j+1]
    slt $t0, $t4, $t3 #$t0 = 0 if $t4 S $t3
    beq $t0, $zero, exit2 #go to exit2 if $t4 S $t3
    move $a0, $s2 #1st parameter of swap is v(old $a0)
    move $a1, $s1 #2nd parameter of swap is j
    jal swap #swap
    addi $s1, $s1, -1 
    j for2tst #jump to test of inner loop
    j print
exit2: 
    addi $s0, $s0, 1 #i = i + 1
    j for1tst #jump to test of outer loop

exit1: 
    lw $s0, 0($sp) #restore $s0 from stack
    lw $s1, 4($sp) #resture $s1 from stack
    lw $s2, 8($sp) #restore $s2 from stack
    lw $s3, 12($sp) #restore $s3 from stack
    lw $ra, 16($sp) #restore $ra from stack
    addi $sp, $sp, 20 #restore stack pointer 
    jr $ra #return to calling routine

    .data
space:.asciiz  " "          # space to insert between numbers
head: .asciiz  "The sorted numbers are:\n"
  .text
print:add  $t0, $zero, $a0  # starting address of array
      add  $t1, $zero, $a1  # initialize loop counter to array size
      la   $a0, head        # load address of print heading
      li   $v0, 4           # specify Print String service
      syscall               # print heading
out:  li   $v0, 1           # specify Print Integer service
      la   $a0, space       # load address of spacer for syscall
      li   $v0, 4           # specify Print String service
      syscall               # output string
      addi $t0, $t0, 4      # increment address
      addi $t1, $t1, -1     # decrement loop counter
      bgtz $t1, out         # repeat if not finished
      jr   $ra              # return

Answer 1

看看你的exit1 子。你最后使用了jr $ra，这意味着它是一个子程序。你在哪里设置返回地址寄存器？您只是分支到这些潜艇；你应该调用他们，使用jal。

或者，在exit1 的末尾，使用j，就像使用exit2 一样。

编辑：您还需要使用jal print，而不是j print。 总是在任何返回 jr $ra 的子上使用 jal，如果子没有使用 jal（或任何链接说明）。