What's wrong with this code? FASM bug maybe?

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alorent

Joined: 05 Dec 2005
Posts: 221

alorent 02 Nov 2009, 12:44

Hello,

I have create a small test to demostrate the error that I'm having.

This is the code:

Code:

format PE GUI 4.0
entry start

include 'win32a.inc'

; define our macro

macro MY_MACRO
{

    local   jmp_label

    jmp     jmp_label

    mov ebx, ebx

    jmp_label:

}

; code starts here

section '.text' code readable executable

  start:
        call    MyProc
        ret

; My test proc

proc MyProc

 push  eax

 jmp     .Exit

 mov ecx, ebx

 MY_MACRO

.Exit:

 pop eax
 ret

endp

The above produces error "Error: undefined symbol MyProc.Exit". If I just comment the line "MY_MACRO" it works fine. Of course, this is quite a dummy macro and example to demostrate the error.

Is this a FASM bug? Because under MASM it works fine.

Thanks!

02 Nov 2009, 12:44

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 02 Nov 2009, 12:47

The labels need to be local to the outer procedure. Use a dot before the macro local labels.

Code:

macro MY_MACRO {
    local .jmp_label
    jmp .jmp_label
    mov ebx, ebx
    .jmp_label:
}

02 Nov 2009, 12:47

alorent

Joined: 05 Dec 2005
Posts: 221

alorent 02 Nov 2009, 18:35

Thanks a lot revolution!

I thought that the "local" inside the macro should do all that work.

Thanks!

02 Nov 2009, 18:35

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20759
Location: In your JS exploiting you and your system

revolution 03 Nov 2009, 01:05

local in macros makes the label local to the macro only, that is, the label is internally make unique with a suffix. This is different from procedural localised labels (with a leading dot).

03 Nov 2009, 01:05

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