Temporary Labels

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Pinecone_

Joined: 28 Apr 2008
Posts: 180

Pinecone_ 20 Nov 2008, 14:53

I've been trying to write my own Proc macros, just for the learning experience.
I'm just going to ignore local stuff for now to avoid complication...
The only problem i've had is defining the argument names at their correct location (Ebp+8+...)
The label directive can define it fine as follows:

Code:

Label Args Dword AT Ebp + 4 + (ArgCount * 4)

however the manual says

Quote:

Each label can be defined only once.

therefore i can't have the same name for arguments in diferent procs... i tried to get around this by restoring it with

Code:

Args EQU

however this resulted in an invalid expression when i used the label.. I thought it was strange that it did not produce an error saying symbol already defined...

Anyway, next I tried defining it like...

Code:

Args EQU Ebp + 4 + (ArgCount * 4)

and restoring with...

Code:

Args EQU

which works, but i need to specify the size every time i want to use it... eg:

Code:

mov eax, dword [argument]

which is not ideal.

So my question: How can i make "Temporary Labels" only avaliable in the proc (restore with the EndP macro) that are size-aware.. so i dont have to specify dword every time i want to use them...? Thanks in advance

Here's the full macro i'm using just to clarify any other questions... (no-one else i've seen seems to write macros like i do.. Razz

it's strange)

Code:

Macro Proc Name, [Args] {
     Common
              
            Label Name
          Push Ebp
            Mov Ebp, Esp
                
            Local ArgCount
              ArgCount = 0
                
    Forward
             IF ~ Args EQ
                        ArgCount = ArgCount + 1
                     Label Args Dword AT Ebp + 4 + (ArgCount * 4)
                        ; Args EQU Ebp + 4 + (ArgCount * 4) 
                End IF
      Common
              
            Macro Ret \{
                  Leave
                       Ret ArgCount * 4
            \}
            
            Macro EndP \{
                 
                    Forward
                             
                            IF ~ Args EQ
                                        Args EQU
                            End IF
                      
                    Common 
                             
                            Purge Ret
                           Purge EndP
                          
            \}
            
}

Last edited by Pinecone_ on 20 Nov 2008, 15:26; edited 1 time in total

20 Nov 2008, 14:53

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20433
Location: In your JS exploiting you and your system

revolution 20 Nov 2008, 14:59

Pinecone_ wrote:

How can i make "Temporary Labels" only avaliable in the proc

Use local, that is what it is for.

20 Nov 2008, 14:59

Pinecone_

Joined: 28 Apr 2008
Posts: 180

Pinecone_ 20 Nov 2008, 15:08

Is local not only for the macro language? Whatever i define in local would not be avaliable for use in between the Proc and EndP if my understanding of them is correct... I don't quite see how that would work.

I wish to use the above macro like...

Code:

Proc Test, Arg1, Arg2, Arg3
       Mov Eax, [Arg1]
Ret
EndP

and have it compiled to...

Code:

Push Ebp
Mov Ebp, Esp
     Mov Eax, [Ebp + 0x08]
Leave
Ret 0x0C

20 Nov 2008, 15:08

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20433
Location: In your JS exploiting you and your system

revolution 20 Nov 2008, 15:20

Have a look at the fasm proc macro in the download to see how it is easily done.

Since proc is a macro you can use local to define labels and then use an equ to map it to the desired programmer selected name.

Code:

local someLabel ;internally defined as someLabel?blahblah
label somelabel ...
MyLabel equ someLabel
mov eax,[MyLabel]

20 Nov 2008, 15:20

Pinecone_

Joined: 28 Apr 2008
Posts: 180

Pinecone_ 20 Nov 2008, 15:30

That makes complete sense, and yet i still managed to fail Razz

After trying what you said, i'm getting error "undefined symbol 'SomeLabel?QT'."
using this...

Code:

Local SomeLabel
IF ~ Args EQ
   ArgCount = ArgCount + 1
     Label SomeLabel Dword AT Ebp + 4 + (ArgCount * 4)
   Args EQU SomeLabel
End IF

20 Nov 2008, 15:30

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20433
Location: In your JS exploiting you and your system

revolution 20 Nov 2008, 16:31

Remember that if and equ are processed at different stages. However since you have not posted the entire macro and it's instantiation code we cannot help you to fix it.

20 Nov 2008, 16:31

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 20 Nov 2008, 19:09

Pinecone_,

You may look at proc macro from STDCALL.INC in earlier versions of fasm. For example, 1.51:

Code:

macro proc name,[arg]                    ; define procedure
 { common
    name:
    virtual at ebp+8
    if ~ arg eq
   forward
     local ..arg
     ..arg dd ?
     arg equ ..arg
   common
     end if
     ..ret = $ - (ebp+8)
    end virtual
    local ..dynamic_data,..dynamic_size
    dynamic_data equ ..dynamic_data
    dynamic_size equ ..dynamic_size
    virtual at ebp - dynamic_size
     dynamic_data: }

20 Nov 2008, 19:09

Pinecone_

Joined: 28 Apr 2008
Posts: 180

Pinecone_ 21 Nov 2008, 00:55

Thank you revolution and baldr. And revolution, i forgot to mention that i edited the first post and gave the whole macro after you posted. Here's the macro now working. (Thank you!)

Code:

Macro Proc Name, [Args] {
 Common
              
            Label Name
          Push Ebp
            Mov Ebp, Esp
                
            Local ArgCount
              ArgCount = 0
                
            IF ~ Args EQ
                Virtual AT Ebp + 8
  Forward
             ArgCount = ArgCount + 1
             Local ..Arg
         ..Arg DD ?
          Args EQU ..Arg
      Common
              End Virtual
         End IF
              
            Macro Ret \{
                  Leave
                       Ret ArgCount * 4
            \}
            
            Macro EndP \{
                 
                    Forward
                             
                            IF ~ Args EQ
                                        Args EQU
                            End IF
                      
                    Common 
                             
                            Purge Ret
                           Purge EndP
                          
            \}
            
}

21 Nov 2008, 00:55

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