Do's and Don'ts of Win32 Programming - Forums

Home » Forums » MAIN » Do's and Don'ts of Win32 Programming

Originally posted by hutch--
You have actually described the convention the wrong way around. Try and connect this much, when you write your OWN procedure, IF you use any of EBX ESI EDI ESP EBP you either preserve it or crash the application most of the time.

No it won't:



.586

.model flat, stdcall



option casemap:none



include <windows.inc>

include <kernel32.inc>

include <user32.inc>



includelib <kernel32.lib>

includelib <user32.lib>

.data

    msgText db  "text",0

.code

    

    func2 proc param:dword

        mov ebx, 1

        mov esi, param

        invoke  MessageBox, NULL, addr msgText, addr msgText, MB_OK

        mov edi, 2

    ret

    func2 endp

    

    func1 proc

        invoke func2, 100

        mov    ebx, 12345

    ret

    func1 endp

    

start:

    invoke  func1

    invoke  ExitProcess, eax

    

end start

Both func1 and func2 trash some of those register but it won't crash.

How does this effect a person who is writing an application ? Simple, if they are going to use any of the registers that require preservation they do so and if they are going to call API functions, they MUST protect EAX ECX EDX if they are being used in the procedure.

Of course you must preserve those since they will be trashed by windows. But that does not mean you can't trash ebx esi edi in your own proc.

Now to address WHAT a callback is under Windows, it is the starting address of a procedure which depending and the type of callback that it is is designed specifically to receive a set number of parameters.

The most important property of a callback is that it's called by windows and that's the only reason you need to adhere to the ebx/esi/edi register preservation.

Now as you choose to try and correct me in the advice I have given to a member, explain to anyone here why EBX ESI EDI must be preserved when they are not used here. You will notice that ESP and EBP are preserved in the normal manner for MASM.

I never said you should save registers if you don't use them.

The simple fact is that EBX ESI EDI are NOT used in this standard system callback so unless your own code uses them, extra preservation is bad code design that serves no purpose.

I would stick to the *convention* as well, but again, it's not a requirement. If you want you don't have to save them. It's your choice.

I will put it to you that feeding new member folklore is incorrect, the convention for register preservation under Windows is well known and not subject to personal opinion.

I just want to make clear that it isn't a requirement, just a convention. It's not *wrong* what I'm saying, but I wouldn't advice not preserving them.

While I support you writing code in any manner that you like, trying to inflict a mistake on other members looking for information is not consistent with the responsibilities you have here.

It's not a mistake..

Thomas
P.S. I might not be able to answer any posts the next couple of days so my reply may be a bit late..

Posted on 2003-04-26 01:02:28 by Thomas

ASM Community