QBasic reverse Need help

[thinkSJ]

First, sorry for my bad endlish. If you know what i say,please help me~
Thanks~

Here is a program maked with QBasic7.1, I reverse it by IDA Pro5.6 and found following SUB:
SEG01sub11728 proc far ; CODE XREF: SEG27sub5741D+19A4P

var_16 = word ptr -16h
var_14 = word ptr -14h

mov cx, 4
mov bx, 0
call far ptr B$ENRD ; Allocate space on stack
;
call near ptr EventChk1
call B$LINA
mov ds:word718E2, 64h ; 'd'
call near ptr EventChk1
call B$LINA
push offset word718E2
call SEG15sub35826
mov [bp+var_14], ax
mov si, 5FCh
mov ax, [bp+var_14]
mov [si+54B4h], ax ; here is problem1
call near ptr EventChk1
call B$LINA
mov ds:word718E4, 64h ; 'd'
call near ptr EventChk1
call B$LINA
push offset word718E4
call SEG15sub35826
mov [bp+var_16], ax
xor si, si
mov ax, [bp+var_16]
mov [si+54B4h], ax ; here is problem2
call near ptr EventChk1
call B$LINA
call far ptr B$EXSA
retf 0
SEG01sub11728 endp

Convert it to following QBasic code:
SUB SEG01sub11728
word718E2% = &H64
var14% = SEG15sub35826%(word718E2%)
'
' How the problem1 Asmcode are converted ?
'
word718E4% = &H64
var16% = SEG15sub35826%(word718E4%)
'
' How the problem2 Asmcode are converted ?
'
END SUB

Thanks fro your helping ~

[burger2227]

You probably will need help from somebody framiliar with ASM or Assembly code in Qbasic. There are some tutorials here:

http://www.petesqbsite.com/sections/tut ... mbly.shtml

Ted

[thinkSJ]

Hi Ted:
Your link is so cool, but can not resolve my problem. I want to convert the AsmCode to
relevant QBasic code.
In problem1, The AsmCode written a memory address [si + 54B4h] and "si" is 5fch, in problem2 "si" is zero.
If "54b4h" is a global var's address, what is it type? an array or a user defined type?

1: if it is a array, like DIM A%(766), when we use the following QBasic code
a%(0) = 1
BC will generate following Asm code:
push 0 ' this is index
push 1
mov bx, OFFSET a%
call B$HARY
mov word ptr[bx], 1

2: if it is a UserType,like:
TYPE UserType
a1 AS INTEGER
a2 AS STRING * &H5f8
a3 AS INTEGER
END TYPE
DIM a AS UserType
a.a1 = 1
The relevant AsmCode is: mov ds:xxxxxxx, 1
Also we can write these code:
POKE VARPTR(a)+&H5fc, 2
The AsmCode is:
mov ax, 36h ; '6'
add ax, 5FCh
into
mov bx, ax
mov ax, 2
mov es, word ptr ds:b$seg
mov es:[bx], al
We can see, there are different~,

I am a QBasic beginner(about 1 month). Is there any other method can let BC generate the destnation AsmCode?

Thanks~

[thinkSJ]

Problem was resloved~ Its a UserType-Array-Var,

Code: Select all

TYPE UserType
    a1    AS  INTEGER
    a2    AS  LONG
    a3    AS  SINGLE
END TYPE

TYPE UserArr
    pData(1)   AS UserType
END TYPE

DIM SHARED aUserData   AS UserArr

aUserData.pData(1).a1 = 1
' Now,BC does not generate B$HARY