I am busy programming a win32 program in assembly with a form and buttons… The problem is windows modify my variables in ram. The place were a store my hInstance and hwnd variables. I have found a workaround, but it is not an elegant solution. I would like to know why windows modify my variables and also were can I find documentation which describe the start up of an application.
MyWndProc:
push EBP
mov EBP, ESP
mov eax, [EBP + 12]
cmp eax, WM_DESTROY
jne MyWndProc_j2
push 0
call PostQuitMessage
jmp MyWndProc_j1
MyWndProc_j2:
cmp eax, WM_CREATE
jne MyWndProc_j1
mov eax, [EBP+8]
push eax
call CreateControls
add esp, 4
MyWndProc_j1:
mov eax, [EBP + 20]
push eax
mov eax, [EBP + 16]
push eax
mov eax, [EBP + 12]
push eax
mov eax, [EBP + 8]
push eax
call DefWindowProcA
pop EBP
ret
segment .data
Wtitle db 'My Window',0
ClassName db 'myWindowClass',0
editClass db 'EDIT',0
buttonName db 'OK',0
buttonClass db 'BUTTON',0
textName db 'My textbox',0
textClass db 'edit',0
formEdit db 'This is just a mem test', 0
windowsVar1 dd 0
windowsVar2 dd 0
windowsVar3 dd 0
windowsVar4 dd 0
windowsVar5 dd 0
windowsVar6 dd 0
windowsVar7 dd 0
windowsVar8 dd 0
aMsg dd 0
hwnd dd 0
hwnd2 dd 0
hwnd3 dd 0
hInstance dd 0
old_proc dd 0
nCmdShow dd 0
hfDefault dd 0
MyWndProc is the callback function from windows. At the 27’th call from windows, it modify the last 7 variables. If I switch the position of the last 8 variables with windowsVarx, then it still modifies hwnd, hwnd2 … without modifying windowsVarx. Where x is from 1 to 8
CreateControls:
push EBP
mov EBP, ESP
push 0
push 0
call GetModuleHandleA
push eax
push IDC_MAIN_BUTTON
mov eax, [EBP+8] ;hwnd
push eax
push 24
push 100
push 220
push 50
mov eax, WS_CHILD
or eax, BS_DEFPUSHBUTTON
or eax, WS_TABSTOP
or eax, WS_VISIBLE
push eax
push buttonName
push buttonClass
push 0
call CreateWindowExA
mov [hwnd2], eax
push DEFAULT_GUI_FONT
call GetStockObject
mov [hfDefault], eax
push 0
mov eax, [hfDefault]
push eax
push WM_SETFONT
mov eax, [hwnd2]
push eax
call SendMessageA
push 0
push 0
call GetModuleHandleA
push eax
push IDC_MAIN_EDIT
mov eax, [EBP+8] ;hwnd
push eax
push 100
push 200
push 100
push 50
mov eax, WS_CHILD
or eax, ES_MULTILINE
or eax, ES_AUTOVSCROLL
or eax, ES_AUTOHSCROLL
or eax, WS_VISIBLE
push eax
push 0
push editClass
push WS_EX_CLIENTEDGE
call CreateWindowExA
mov [hwnd3], eax
push 0
mov eax, [hfDefault]
push eax
push WM_SETFONT
mov eax, [hwnd3]
push eax
call SendMessageA
push Wtitle
push 0
push WM_SETTEXT
mov eax, [hwnd3]
push eax
call SendMessageA
pop EBP
ret
The following function is the message loop, which collect and dispatch.
MyMessageLoop:
push 0
push 0
push 0
push aMsg
call GetMessageA
cmp eax, 0
je MyMessageLoop_j1
push aMsg
call TranslateMessage
push aMsg
call DispatchMessageA
jmp MyMessageLoop
MyMessageLoop_j1:
ret
Where do I start? Your code formatting is very hard to read. Hope a Uni is not teaching you it. Anyways, your WindowProc was VERY wrong. After EVERY message you handle, you DO NOT call DefWindowProc, most of the messages you just return 0 in eax.
After your call to CreateControls, you don’t need add esp, 4 as long as at the end of CreateControls you do ret 4 or ret 4 * NumOfParamsPassed.
I fixed your WindowProc and the window now shows. I also removed the many unneeded movs.