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xine-2.010
/-----------------------------\
| Xine - issue #2 - Phile 010 |
\-----------------------------/
Coding in 32 bit assembly for win95
by jhb
Most information for coding in Windows is done in C++ or other
high level languages. This leaves the virii writer, traditionally someone
who codes in Assembly, at a loss. To make matters worse even VxD's are being
written in C++ or worse Visual C. MS is making Assembly information harder to
get and less needed for the average programmer. Well with some digging into
the DDK's information and SDK it is possible to remedy this and translate the
C information into usable Assembly format. With the advent of tasm5 and masm6
would be 32 bit assembly coders are blessed with the ability to "easily" use
Win32 Api with a minimum of work.
Here is a small do nothing win32 code which beleive it or not will compile
to 4096 bytes... yeesh talk about "Fatware"
.386
.model flat
extrn ExitProcess:PROC
.data ;the data area
dummy db 0
.code ;executable code starts here
HOST:
push LARGE -1 ;equ to int 20 com dos file call
call ExitProcess ;ends the program
end HOST
Now if we check the Docs for a C program to call ExitProcess
ExitProcess( UINT uExitCode)
Simply put this means the the return exit code is place on the stack
and then the API is called. Ok lets try one that returns info and needs
more then one item push on the stack.
int MessageBox(HWND hwndOwner, LPCTSTR lpszText,
LPCTSTR lpszTitle, UINT ustyle)
lpszText simple means some text ending in a 00h (oops the A at the end of
the MessageBox means Ascii, if W it means unicode, all the routines that
could deal with text have a A or W at the end just to confuse us)
lpszTitle some text to be used as the title and ending in 00h
int in front means that something will be returned to us in the EAX reg
* important thing to know here is we push the items from last to first*
* so the style flags will be first then the title ... *
Ok but the book now says possible choices are MB_OK and a list of others
well dig abit into the SDK winuser.h and this pops up
* MessageBox() Flags
*/
#define MB_OK 0x00000000L
#define MB_OKCANCEL 0x00000001L
#define MB_ABORTRETRYIGNORE 0x00000002L
#define MB_YESNOCANCEL 0x00000003L
#define MB_YESNO 0x00000004L
#define MB_RETRYCANCEL 0x00000005L
ok so we push 0000000 for a style flag and we get the ok button
so that should make the Assembly call look like below
Now this is simple a call to creata a pop up message box its in user32.dll
but all we need to do in tasm5.0 is define this
extrn MessageBoxA:PROC
then
mov eax, 0 ;this is the style
push eax ;
mov eax, offset title ; points to a zero ended string
push eax ;
mov eax,offset mess ; points to a zero ended string
push eax ;
mov eax,0 ; this should be the handle
push eax ;of the owner window Iam telling
;win95 there is no owner
call MessageBoxA ; ok call away
As for the return int it will be in EAX in this case you could
check eax and you should get IDOK or 1 which says the ok button was hit
again this was found in winuser.h
* Dialog Box Command IDs
*/
#define IDOK 1
#define IDCANCEL 2
#define IDABORT 3
#define IDRETRY 4
#define IDIGNORE 5
#define IDYES 6
#define IDNO 7
Well I admit there is much more to this Win32 assembly stuff but this basic
info should allow anyone with some time to write 32Assembly code with a
minimal of problems. It is alot like finding a empty house to explore, I know
as a kid I love to explore and play with things. This exploring of Win32
assembly is just as fun . ;) Read Vlad for more info on assembly for windows
sadly thats the only other place I have seen this topic expored in reasonable
language. I suspect that if MS could a law requiring people to be tested
and registered before Assmblers were sold to them, they would. Assembly
coders have to much power over their code for MS to feel safe besides only
in Assembly can you see what they at MS do not want you to see. ;)
Have fun and if you find anything interesting while your exploring drop me
some e-mail.
