遇到了在我的随机数数组排序程序中找到无效内存访问的问题。

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英文:

Having trouble finding the invalid memory access in my random number array sorting program

问题

在你的代码中，似乎有一些问题。不过你提到的具体错误信息是 "Access violation executing location 0x00000064"，这通常表示访问了无效的内存位置。我会检查你的代码以寻找潜在的问题。

首先，我注意到在 sortList 过程中，你使用了寄存器 edx，但没有在使用之前清除它的值。确保在使用 edx 之前将其清零。

另外，在 displayListDescending 过程中，你对 esi 进行了递减操作，但没有检查是否越界。请确保 esi 不会越界到数组之外。

最后，确保你的数组足够大来容纳 request 中指定的数量，否则可能会导致访问无效内存。

请检查这些问题，看看是否有助于解决你的异常问题。如果问题仍然存在，你可能需要更详细地调试以找到问题的确切位置。

英文:

I am coding this for an assignment, where I am required to make an array in MASM and assign it random numbers given a number input. I am past the selection sort part of my assignment, and I am having trouble finding out where I am not accessing the write memory. The error code that I get is:

> Exception thrown at 0x00000064 in Project.exe: 0xC0000005: Access violation executing location 0x00000064.

And here is the rest of my code:

  1. INCLUDE Irvine32.inc
  3. .data
  4.     instructions BYTE "This program generates random numbers in the range [100 .. 999], displays the original list, sorts the list, and calculates the median value. Finally, it displays the list sorted in descending order.",0
  5.     unsorted    BYTE "The unsorted random numbers:",0
  6.     median      BYTE "The median is ",0
  7.     sorted      BYTE "The sorted list:",0
  8.     prompt      BYTE "How many numbers should be generated? [10 .. 200]: ",0
  9.     invalid     BYTE "Invalid input",0
  10.     newline     BYTE 0DH, 0AH, 0
  11.     spaceBar    BYTE " ", 0
  12.     array       DWORD 200 DUP(?)
  13.     request     DWORD ?
  14.     medianValue DWORD ?
  16. .code
  17.     main PROC
  18.           call introduction
  19.           call getData
  20.           call generateRandomNumbers
  21.           call displayList
  22.           call calculateMedian
  23.           call displayMedian
  24.           call sortList
  25.           call displayListDescending
  27.           exit
  28.      main ENDP
  30.      introduction PROC
  31.           mov edx, OFFSET instructions
  32.           call WriteString
  33.           call Crlf
  34.           ret
  35.      introduction ENDP
  37.      getData PROC
  38.           mov edx, OFFSET prompt
  39.           call WriteString
  40.           call ReadInt
  41.           cmp eax, 10
  42.           jl invalidInput
  43.           cmp eax, 200
  44.           jg invalidInput
  45.           mov [request], eax
  46.           ret
  48.           invalidInput:
  49.           mov edx, OFFSET invalid
  50.           call WriteString
  51.           call Crlf
  52.           jmp getData
  53.      getData ENDP
  55.      generateRandomNumbers PROC
  56.           mov ecx, [request]
  57.           mov esi, OFFSET array
  58.           generateLoop:
  59.                call RandomRange ; Generates random number in the range [0, 899]
  60.                add eax, 100 ; Adjust the range to [100, 999]
  61.                mov [esi], eax
  62.                add esi, 4
  63.                loop generateLoop
  64.           ret
  65.      generateRandomNumbers ENDP
  67.      displayList PROC
  68.           mov edx, OFFSET unsorted
  69.           call WriteString
  70.           call Crlf
  71.           mov edx, OFFSET newline
  72.           call WriteString
  73.           mov ecx, [request]
  74.           mov esi, OFFSET array
  75.           displayLoop:
  76.           mov eax, [esi]
  77.           call WriteInt
  78.           mov edx, OFFSET spaceBar
  79.           call WriteString
  80.           add esi, 4
  81.           loop displayLoop
  82.           call Crlf
  83.           ret
  84.      displayList ENDP
  86.      calculateMedian PROC
  87.           mov ecx, [request]
  88.           shr ecx, 1
  89.           mov esi, OFFSET array
  90.           mov eax, [esi+ecx*4]
  91.           mov [medianValue], eax
  92.           ret
  93.      calculateMedian ENDP
  95.      displayMedian PROC
  96.           mov edx, OFFSET median
  97.           call WriteString
  98.           call Crlf
  99.           mov edx, OFFSET newline
  100.           call WriteString
  101.           mov edx, [medianValue]
  102.           call WriteInt
  103.           call Crlf
  104.           ret
  105.      displayMedian ENDP
  106.      
  107.     sortList PROC
  108.           mov ecx, [request]
  109.           mov esi, OFFSET array
  110.           mov ebx, OFFSET array
  111.           mov edi, ecx
  113.           sortLoop:
  114.                xor edx, edx
  115.                mov eax, [esi]
  116.                innerLoop:
  117.                     add ebx, 4
  118.                     cmp ebx, edi
  119.                     jge skipExchange
  120.                     mov edx, [ebx]
  121.                     cmp edx, 100
  122.                     jge skipExchange
  123.                     mov eax, edx
  124.                     mov edi, ebx
  125.                skipExchange:
  126.                     loop innerLoop
  128.                cmp esi, edi
  129.                je skipSwap
  131.                push eax
  132.                push [esi]
  133.                call exchangeElements
  134.                skipSwap:
  135.                     add esi, 4
  136.                     cmp edx, 0
  137.                     jne sortLoop
  138.                
  139.                ret
  141.    sortList ENDP
  143.    displayListDescending PROC
  144.           mov edx, OFFSET newline
  145.           call WriteString
  146.           mov ecx, [request]
  147.           mov esi, OFFSET array
  149.           mov eax, ecx           ; Store the value of ecx in eax
  150.           dec eax                ; Decrement eax to get (ecx-1)
  151.           mov ebx, 4
  152.           mul ebx
  153.           shl eax, 2             ; Multiply by 4 (shift left by 2)
  154.           add esi, eax           ; Add the offset to the base address of the array
  156.           displayLoop:
  157.                mov eax, [esi]
  158.                call WriteInt
  159.                mov edx, OFFSET spaceBar
  160.                call WriteString
  161.                sub esi, 4
  162.                loop displayLoop
  164.           call Crlf
  165.           ret
  166.     displayListDescending ENDP
  170.     exchangeElements PROC
  171.           push edx
  172.           mov edx, [esp+12]
  173.           mov ecx, [esp+8]
  174.           mov [esp+12], ecx
  175.           mov [esp+8], edx
  176.           pop edx
  177.           ret
  178.      exchangeElements ENDP
  180. END main

My best guess where the exception is being thrown is in the displayListDescending procedure. I have tried to simplify the registers and have even tried to keep track of what ESI is even tracking.
I'd appreciate any help I possibly can get.

答案1

得分: 1

The exception

异常

我最好的猜测是异常被抛出的地方在 displayListDescending 过程中。

确实，在这里，您的程序在数组之外的内存中读取数据！计算数组中最后一个元素的偏移错误地将索引乘以4 重复两次。

  1. mov  ecx, [request]
  2. mov  esi, OFFSET array
  3. mov  eax, ecx
  4. dec  eax
  5. mov  ebx, 4             <<<< 1st x 4
  6. mul  ebx
  7. shl  eax, 2             <<<< 2nd x 4
  8. add  esi, eax

解决方法之一是写成：

  1. mov  ecx, [request]
  2. lea  esi, [array + ecx * 4 - 4]

Random numbers

随机数

  1. generateRandomNumbers PROC
  2.    mov  ecx, [request]
  3.    mov  esi, OFFSET array
  4.  generateLoop:
  5.    call RandomRange ; 在范围[0, 899]内生成随机数
  6.    add  eax, 100    ; 调整范围为[100, 999]
  7.    mov  [esi], eax
  8.    add  esi, 4
  9.    loop generateLoop
  10.    ret
  11. generateRandomNumbers ENDP

您没有在范围[0, 899]内生成随机数。要实现这一点，您需要在 call RandomRange 前将 ECX 设置为 900。但由于这会与当前的循环计数器冲突，您需要使用另一个寄存器来控制循环：

  1. generateRandomNumbers PROC
  2.    mov  edi, [request]
  3.    mov  esi, OFFSET array
  4.   generateLoop:
  5.    mov  ecx, 900
  6.    call RandomRange ; 在范围[0, 899]内生成随机数
  7.    add  eax, 100    ; 调整范围为[100, 999]
  8.    mov  [esi], eax
  9.    add  esi, 4
  10.    dec  edi
  11.    jnz  generateLoop
  12.   ret
  13. generateRandomNumbers ENDP

The median

中位数

  1. mov edx, [medianValue]
  2. call WriteInt

传递给 WriteInt 的输入位于 EAX 中。

The selection sort

选择排序

sortList 及其附带的 exchangeElements 过程无法挽救。它们包含了许多难以解释的操作，这也使得很难确定它是否真正是选择排序，而不是其他排序方法。

我编写了这个选择排序算法，附带可视化演示，以便您了解它的工作原理。尽管它使用了16位寄存器，但将其移植到32位应该不难。

英文:

The exception

> My best guess where the exception is being thrown is in the displayListDescending procedure.

Indeed, that is where your program reads from memory outside of the array! The calculation of the offset to the last element in the array is erroneously multiplying the index by 4 doing it twice.

> mov ecx, [request]
> mov esi, OFFSET array
> mov eax, ecx
> dec eax
> mov ebx, 4 <<<< 1st x 4
> mul ebx
> shl eax, 2 <<<< 2nd x 4
> add esi, eax

One way to solve it is to write:

  1. mov  ecx, [request]
  2. lea  esi, [array + ecx * 4 - 4]

Random numbers

> generateRandomNumbers PROC
> mov ecx, [request]
> mov esi, OFFSET array
> generateLoop:
> call RandomRange ; Generates random number in the range [0, 899]
> add eax, 100 ; Adjust the range to [100, 999]
> mov [esi], eax
> add esi, 4
> loop generateLoop
> ret
> generateRandomNumbers ENDP

You are not generating a random number in the range [0,899]. For that to happen you need to set ECX=900 before call RandomRange. But since that would clash with the current loop counter, you need to use another register to control the loop:

  1. generateRandomNumbers PROC
  2.    mov  edi, [request]
  3.    mov  esi, OFFSET array
  4.   generateLoop:
  5.    mov  ecx, 900
  6.    call RandomRange ; Generates random number in the range [0, 899]
  7.    add  eax, 100    ; Adjust the range to [100, 999]
  8.    mov  [esi], eax
  9.    add  esi, 4
  10.    dec  edi
  11.    jnz  generateLoop
  12.   ret
  13. generateRandomNumbers ENDP

The median

> mov edx, [medianValue]
> call WriteInt

The input to WriteInt goes in EAX.

The selection sort

The sortList and its accompanying exchangeElements procedures are not salvageable. They contain a lot of inexplicable operations that also make it hard to even find out if it is an actual selection sort and not some other sorting method.
I wrote this selection sort algorithm with a visual run-through so you can understand how it works. Although it uses 16-bit registers, porting it to 32-bit should not be difficult.

答案2

得分: 0

exchangeElements 可能需要一个 "ret 8"，因为在调用它之前你压入了两个双字。

英文:

exchangeElements probably needs a "ret 8" since you push two dwords before calling it.

huangapple
  • 本文由 发表于 2023年6月1日 05:22:23
  • 转载请务必保留本文链接：https://go.coder-hub.com/76377390.html
  • assembly
  • exception
  • irvine32
  • masm
  • x86
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