masm to fasm for newb

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chorus

Joined: 16 Mar 2004
Posts: 23

chorus 16 Mar 2004, 16:28

Hello all,
I've downloaded fasm and think it's wicked (nice job Privalov) and I'm converting my old masm syntax code to fasm. Naturally, there are some differences. I've taken a quick look through this board but didn't really find the answers that I was looking for (I'm sure they're here somewhere...)

I have 3 problems I'm trying to address. Can someone please help me out?

1) How do you declare a local stack variable for a proc? in masm I would do

Code:

MyProc proc a,b:dword
LOCAL whatever:dword

2) How do you get the size of a structure? ex.

Code:

mov wc.cbSize, sizeof WNDCLASSEX

3) How do you use a reg as a pointer to a struc? ex.

Code:

mov [ebx].WNDCLASSEX.cbSize,48

How would you assume it?

If anyone could let me know how these things can be done I'd greatly appreciate it.

Thanks
--Chorus

16 Mar 2004, 16:28

pelaillo
Missing in inaction

Joined: 19 Jun 2003
Posts: 878
Location: Colombia

pelaillo 16 Mar 2004, 16:44

1. use proc macro

Code:

proc MyProc,a,b
 dd wathever
 begin
 mov eax,[wathever]
 add eax,[a]
 return
endp

2. use struct macro

Code:

 mov [wc.cbSize],WNDCLASSEX
;or
 mov [wc.cbSize],sizeof.WNDCLASSEX

3. use virtual directive

16 Mar 2004, 16:44

chorus

Joined: 16 Mar 2004
Posts: 23

chorus 16 Mar 2004, 17:10

Thanks! Seems simple enough Smile

Just to make sure though, with the "dd" syntax for a local that does define it as a variable on the stack right? As opposed to defining a dword in the middle of my code?

--Chorus

16 Mar 2004, 17:10

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 16 Mar 2004, 17:34

chorus wrote:

Thanks! Seems simple enough

Well, here are some details. Smile

There is standard macro library in FASMW package that provides macroses for these constructions: proc, struct, invoke, stdcall etc.
Its syntax is a little diferent from the above examples:

Code:

proc ProcName, arg1, arg2, .... argN
; local variables, they will be created in the stack.
  .name1 dd ?
  .name2 dd ?
  .name3 rb 100 ; you can use every data definition instruction here.
enter
   ; the body of the procedure.
return

Because of some reasons (more power and flexibility) the project Fresh and developers working on FASMs standard library prefere to use a little bit different proc definitions:

Code:

proc ProcName, arg1, arg2, .... argN
; local variables, they will be created in the stack.
  .name1 dd ?
  .name2 dd ?
  .name3 rb 100 ; you can use every data definition instruction here.
begin
  ; the body of the procedure.
      return

 ; possibly another code
      return
endp

You can download this variant from Fresh package here:
http://fresh.flatassembler.net

Also I prefer to not use following construction:

Code:

 mov [wc.cbSize],WNDCLASSEX

It is absolutely equivalent to:

Code:

mov [wc.cbSize],sizeof.WNDCLASSEX

but, "sizeof." variant is more readable and clear.

About using structures with register indirect addressing:

Code:

    mov  [esi+WNDCLASSEX.cbSize], sizeof.WNDCLASSEX

FASM is very flexible to do this kind of things, so after some experience, you will find the most comfortable for you way.

Regards.

16 Mar 2004, 17:34

chorus

Joined: 16 Mar 2004
Posts: 23

chorus 16 Mar 2004, 20:06

Thank you JohnFound. Details are good. I like details Smile

Another question: How can I pass local variables to a proc through invoke?

I try to do this:

Code:

proc InitClass,lpszClassName,lpfnWndProc,hIcon
.wc WNDCLASSEX
        enter
        ...
        invoke RegisterClassEx,.wc
        return

but the invoke to RegisterClassEx does not assemble. I have to "lea eax,[.wc]" and then "invoke RegisterClassEx,eax" (the same thing, I know, but it would be convenient to not have to do that).

Thanks again
--Chorus

16 Mar 2004, 20:06

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 16 Mar 2004, 20:14

chorus wrote:

Another question: How can I pass local variables to a proc through invoke?....
I have to "lea eax,[.wc]" and then "invoke RegisterClassEx,eax" (the same thing, I know, but it would be convenient to not have to do that).

This is not "the same thing". It is the "only way" to make it. MASM provide this behaviour hidden from the programmer. Of course it is possible to make the same behaviour for invoke macro for FASM, but I don't think this is good programming practice, for assembler.

Regards.

16 Mar 2004, 20:14

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