Macro aliasing and forward references

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nyrtzi

Joined: 08 Jul 2006
Posts: 192
Location: Off the scale in the third direction

nyrtzi 10 Oct 2009, 13:37

So one variant of the code looks like this...
(this is just a test... not real app code)

Code:

format elf

macro proc name
{
    local start
    macro name
    \{
        call start   
    \}
    macro endp 
    \{
        pop eax
        ret
        purge endp
    \}
    start:
    push eax
}

start:
    goo
    ret

proc goo
    nop
endp

When I try to assemble this FASM says: "error: illegal instruction." because "goo" isn't defined yet. So of course if I move the "proc goo ... endp" before "start:" this code will assemble without any problems.

So the question is that is there a way to make macro forward references like this work?

Of course I could always just do a "call goo" instead of plain "goo" but then again again aren't I using macros in the first place exactly because I want to avoid unnecessary typing?

The bigger problem and the actual main issue is that this doesn't work:

Code:

proc foo
    zoo
endp

proc zoo
    foo
endp

In this case re-ordering doesn't help at all.
Any ideas on how I can make this work i.e., to assemble properly?
Or should I just give up on the idea of being able to have macro aliases like these for procedure calls?

10 Oct 2009, 13:37

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20451
Location: In your JS exploiting you and your system

revolution 10 Oct 2009, 14:04

You can't forward reference macros, rept, irp, struc, define. The preprocessor is single pass only.

10 Oct 2009, 14:04

nyrtzi

Joined: 08 Jul 2006
Posts: 192
Location: Off the scale in the third direction

nyrtzi 10 Oct 2009, 14:17

The preprocessor does only a single pass? Weird... oh well.

I guess I'll just have to use sed or some other tool to do some custom preprocessing and add that to my Makefile.

Thanks for the pointer.

10 Oct 2009, 14:17

nyrtzi

Joined: 08 Jul 2006
Posts: 192
Location: Off the scale in the third direction

nyrtzi 10 Oct 2009, 18:11

Just for future reference in case someone is doing something similar...

The actual source code. Assumed to be in the src/ directory.

Code:

format elf

include '../obj/aliases.inc'

macro proc name
{
    macro endp 
    \{
        ; replace this line with cleanup code
        ret
        purge endp
    \}
    _#name:
    ; replace this line with initialization code
}

main:
    goo
    ret

proc goo
    ; do something
endp

Put this for example in a Makefile.

Code:

find src/ -iname '*.asm' | xargs awk '/^proc/ { printf("macro %s { call _%s }\n",$2,$2);  }' > obj/aliases.inc

This of course assumes that you have some kind of a shell environment available with 'find', 'xargs', 'awk' and 'make'. I'm doing this on a CentOS virtualbox...

10 Oct 2009, 18:11

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