Accessing dynamic char array in inline assembly (VS2012)

Question

I'm working in Visual Studio 2012 Professional, i have this code:

 char* array = (char*) malloc(100);
 array[0] = 'H'; array[1] = 'e'; array[2] = 'l'; array[3] = 'l';array[4] = 'o';

 __asm {
    // Missing code here
    }

How can i access, for example, the chars in the array using inline assembly? I tried this but it works only for the first character in the array:

 mov eax, array[0]
 mov al, [eax] // Now al contains the 'H'

Buf if i change the code to "mov eax, array[1]" it doesn't work anymore (access violation). How can i loop trough the array?

EDIT, SOLVED (i can't answer my own question for 8 hours) : I found what was wrong with the code:

mov eax, array[0]
mov al, [eax]

actually works, but the eax value gets changed because i modify the al register that's part of the eax register, so when i put it in a loop the eax value is no longer valid. Changing eax to ebx, for example, makes it work without any problem.

You need to load effective address. lea eax, array then increment eax whenever you want just as a pointer. Then access as mov al,[eax] but this may only valid for 32 bit system. — huseyin tugrul buyukisik
@huseyin This unfortunately doesn't work, the final value in the al register is not any of the characters i put in the array. — denidare

denidare denidare · Accepted Answer · 2013-07-19T12:03:46

I found what was wrong with the code:

mov eax, array[0]
mov al, [eax]

actually works, but the eax value gets changed because i modify the al register that's part of the eax register, so when i put it in a loop the eax value is no longer valid. Changing eax to ebx, for example, makes it work without any problem.

Accessing dynamic char array in inline assembly (VS2012)

1 Answers