MIPS中的buggy递归printtree函数

Question

#------start code---------------------------------
#   in: $a0, the parent node that 
#---------------------------------------
printtree:


    subu $sp,$sp,8
    sw  $ra,4($sp)  #save ra
    sw  $a0,8($sp)  #push node
    lw  $a0,12($sp) #access argument node to $a0
    j   ptexit

ptloop:
    subu $sp,$sp,4  
    lw  $a0,4($a0)
    sw  $a0,4($sp)  #push [esi+4]
    jal printtree   #call printtree2    
    add $sp,$sp,8

    lw  $a1,0($a0)  #at this point $a0 holds a node 
    lw  $a1,0($a1)
    jal printInteger    #this function just prints value of $a1
    lw  $a0,12($a0)

ptexit:

    bnez    $a0,ptloop      #jump ptloop if $a0 ne to zero

    lw  $ra,4($sp)
    lw  $a0,8($sp)      #get the returned values from the stack back to $a0
    add $sp,$sp,8
    jr  $r              #go to $ra
#----------end code--------

上面的代码应该打印从最小到最高的二叉树 给定顶部节点，在某处，某种程度上会破坏堆栈，导致异常。非常感谢

Answer 1

最近修复了它，并且据我测试它工作正常。使用它，将父节点传递给0（$ sp），如下面的代码：

sub $sp,$sp,4
sw  $v1,0($sp)
jal printtree
add $sp,$sp,4

----------------------------------------------- -----

 printtree:

    sub $sp,$sp,8
    sw  $a0,0($sp)  #save orig $a0 as new TOS
    sw  $ra,4($sp)  #save return address as TOS+4
    lw  $a0,8($sp)  #access param1 in TOS+8

    j   leftmost

recur:
    sub $sp,$sp,4   
    lw  $a1,4($a0)  #access node->left
    sw  $a1,0($sp)  #push it to the stack
    jal printtree


    lw  $a1,0($a0)  # $a1 should contain node->data
    jal printInteger    # calls a syscall function that prints $a1 value to console

    #node is assumed to be in $a0
    lw  $a0,8($a0)  #access node->right

leftmost:
    bne $a0,$zero,recur
    lw  $a0,0($sp)  #hold the previous node
    lw  $ra,4($sp)  #hold the return address
    add $sp,$sp,12
    jr  $ra

----------------------------------------------- -----