Confused about generated code

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Jerry

Joined: 24 Dec 2016
Posts: 18
Location: Zeist, Netherlands

Jerry 31 Dec 2016, 12:26

Hello,

I've encountered something i do not understand in fasmg (hll54).
What i am attempting is to write a proc macro that takes some parameters.
An example would be

Code:

proc dlgproc, 8, 4, HWND, MSG, WPARAM, LPARAM, LOCAL1 .......
        ...
end proc

One can then access them by [HWND] or [LOCAL1] etc.

The first parameter is how many qwords to reserve for the stack unconditionally (room for api calls).
The second is the amount of actual arguments (a dlgproc has 4), and also allocate stack for that to back them up
for more than 4 arguments one needs to look beyond the returnaddress of the caller and it's shadow space and find the other ( > 4) arguments stored right to left (that part is't working yet but doesn't matter for this question)
Any additional argument names after the formal ones will be made local variables.

Attached is procdemo.zip that consist of procdemo.asm and procdemo.png (a screenshot from x64dbg that shows the generated code)

The line 'mov rax,qword ptr ss:[ ... ]' is repeated 4 times, the following
'mov qword ptr ss:[rsp+60], rax' only once (which is correct and even the correct offset)
But they are generated within the same 'if', that's the part i don't understand, what am i missing ?

Thanks in advance

Description:	Example code	Download
Filename:	procdemo.zip
Filesize:	71.42 KB
Downloaded:	512 Time(s)

31 Dec 2016, 12:26

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 31 Dec 2016, 12:54

The MOV instructions you refer to are generated by this fragment of source:

Code:

        mov rax, [HWND]
        mov rax, [MSG]
        mov rax, [WPARAM]
        mov rax, [LPARAM]
        mov [LOCAL1], rax

while the IF block you mention is not processed at all. This is because the "count > argcount" condition is fulfilled and causes a BREAK.

31 Dec 2016, 12:54

Jerry

Joined: 24 Dec 2016
Posts: 18
Location: Zeist, Netherlands

Jerry 31 Dec 2016, 13:24

Thanks,

I still have a lot to learn (then again, who doesn't).
Will be reading the documentation again.

Regards

31 Dec 2016, 13:24

Jerry

Joined: 24 Dec 2016
Posts: 18
Location: Zeist, Netherlands

Jerry 31 Dec 2016, 13:51

Looked again ....

It actually works, i was looking for the (my) handling of any (not local)) parameter beyond 4.
The example proc usage i sent was 4 parameters and 1 local so there was no 5 parameters whatsoever to begin with.
Second post, second time overlooking something ...

Sorry for taking up unnecessary time.

31 Dec 2016, 13:51

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8351
Location: Kraków, Poland

Tomasz Grysztar 31 Dec 2016, 15:01

By the way, IRP/ITERATE allows to use % and %% parameters to access the number of current iteration and total count, so instead of:

Code:

irp arg, args
                      
        count = count + 1
                        
        if count > argcount

you can simply use:

Code:

irp arg, args
                        
        if % > argcount

31 Dec 2016, 15:01

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