Error in assembly x86: Access violation writing location 0x0081D45C

Question

I want to put the elements from the x[] array >=10 in the vmic[] array, and the others in the vmare[] array. But it throws an error: Access violation writing location 0x0081D45C, when I want to copy the element in one array and I don't know what to do. Thank you in advance!

#include <iostream>

using namespace std;

int main()
{
    //I want to put the elements >=10 in the vmic[] array, and the others int the vmare[] array.
    //until the element in the array is 0
    int x[] = { 1,2,3,4,5,14,22,0 };
    int vmic[10];
    int vmare[10];
    int n = 10;
    int k1 = 0; //vmic
    int k2 = 0; // vmare
    _asm {
        mov eax, 0; //index
        lea ebx, x; 
        lea ecx, vmic; 
        lea edx, vmare; 
        mov esi, n; //val 10
    bucla:
        cmp[ebx + 4 * eax], 0;
        je afara;
        cmp[ebx + 4 * eax], esi;
        jge mai_mare_egal;
        inc k1;
        mov edi, [ebx + 4 * eax]; 
        mov[ecx + 4 * k1], edi;
    mai_mare_egal:
        inc k2;
        mov edi, [ebx + 4 * eax];
        mov[edx + 4 * k2], edi;
    inc eax;
    jmp bucla;
    afara:
    }
    int i;
    for (i = 0; i <= 6; i++)
    {
        printf("% d", x[i]);
    }
    printf("\n");
    for (i = 0; i <= k1; i++)
    {
        printf("% d", vmic[i]);
    }
    printf("\n");
    for (i = 0; i <= k2; i++)
    {
        printf("% d", vmare[i]);
    }
    return 0;
}

Answer 1

I tried debugging this in VS2022, and it gets the line-numbers mixed up sometimes. Better to debug in the Disassembly window ... Also, there was some pretty weird stuff happening in the Disassembly window regarding the on-the-fly pointer arithmetic. For example, this line:

mov[edx + 4 * k2], edi;

... became this:

mov         dword ptr k2[edx*4],edi  

It's been 20+ years since I last wrote assembly, but that looks weird to me. It looks like it's treating k2 as a dword array, and edx as the offset into that array ... which isn't right.

Anyway, I had a go at fixing it.

#include <iostream>

using namespace std;

int main()
{
  //I want to put the elements >=10 in the vmic[] array, and the others int the vmare[] array.
  //until the element in the array is 0
  int x[] = { 11,2,3,4,5,14,22,0 };
  int vmic[10];
  int vmare[10];
  int n = 10;
  _asm {
    mov eax, 0; //index
    lea ecx, vmic;
    lea edx, vmare;
    mov esi, n; //val 10
  bucla:
    lea ebx, x;
    add ebx,eax
    cmp dword ptr[ebx], 0;
    je afara;
    cmp [ebx], esi;
    jge mai_mare_egal;
    mov edi, [ebx];
    mov [ecx], edi;
    add ecx,4;
    add eax, 4;
    jmp bucla;
  mai_mare_egal:
    mov edi, [ebx];
    mov [edx], edi;
    add edx,4;
    add eax, 4;
    jmp bucla;
  afara:         
    mov dword ptr [edx], 0
    mov dword ptr [ecx], 0
  }
  int i;
  for (i = 0; x[i]; i++)
    printf("% d", x[i]);
  printf("\n");
  for (i = 0; vmic[i]; i++)
    printf("% d", vmic[i]);
  printf("\n");
  for (i = 0; vmare[i]; i++)
    printf("% d", vmare[i]);
  return 0;
}