macro use inside repeat block: symbol already defined

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redsock

Joined: 09 Oct 2009
Posts: 430
Location: Australia

redsock 25 Oct 2016, 22:00

Admittedly my board search skills are lacking, so apologies as I am sure this has already been asked before...

The below code results in:

Code:

repmacro.asm [14]:
                do_something
repmacro.asm [11] do_something [5]:
.label:
error: symbol already defined.

... What is the correct way to do this? Code:

Code:

        format ELF64

public _start
_start:

macro do_something {
        local   .label

        jmp     .label
        dd      1,2,3,4
.label:
}
        repeat 8
                do_something
        end repeat

        mov     eax, 60         ; exit
        xor     edi, edi        ; return code
        syscall

_________________
2 Ton Digital - https://2ton.com.au/

25 Oct 2016, 22:00

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 25 Oct 2016, 22:06

You will need to use rept.

Code:

        rept 8 {
                do_something
        }

When you use repeat the code inside is assembled multiple times. When you use rept the code inside is generated multiple times. You need the local label to be generated multiple times so that it is unique each time it is generated.

25 Oct 2016, 22:06

redsock

Joined: 09 Oct 2009
Posts: 430
Location: Australia

redsock 25 Oct 2016, 22:18

thanks for that... rept versus repeat means that % can't be used ... so iteration counts have to be done manually then? e.g. the following code doesn't do what I want:

Code:

        format ELF64

public _start
_start:

macro do_something i* {
        local   .label

        jmp     .label
        dd      i,i+1,i+2,i+3
.label:
}
        rept 8 {
                do_something %
        }

        mov     eax, 60         ; exit
        xor     edi, edi        ; return code
        syscall

_________________
2 Ton Digital - https://2ton.com.au/

25 Oct 2016, 22:18

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 25 Oct 2016, 22:21

You can use an iteration counter with rept:

Code:

rept 8 x {
  do_something x
}

25 Oct 2016, 22:21

redsock

Joined: 09 Oct 2009
Posts: 430
Location: Australia

redsock 25 Oct 2016, 22:24

lol must've missed that in the docs, hahah, thx! Straight from the docs:

Code:

So this:

    rept 3 counter
     {
        byte#counter db counter
     }

will generate lines:

    byte1 db 1
    byte2 db 2
    byte3 db 3

Care to delete my obvious idiotic questions for me then? hahah

As an aside, perhaps it is because of my "lean" use of macros in the first place that I have never had to use rept instead of repeat ... so much code and still learn new tricks Smile

mucho gracias

25 Oct 2016, 22:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20299
Location: In your JS exploiting you and your system

revolution 26 Oct 2016, 00:48

redsock wrote:

Care to delete my obvious idiotic questions for me then?

I won't delete it. This can be instructive to others.

26 Oct 2016, 00:48

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