Detecting fasm vs fasm2 / writing compatible macros

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Ping

Joined: 27 Feb 2026
Posts: 2

Ping 27 Feb 2026, 18:54

Hi all,

Is there a reliable way (at assembly time) to detect whether the source is being assembled by FASM 1.x or FASM2?

I have an .inc file I’d like to reuse with FASM2. Most of it works, but a couple of macros rely on the older macro style and need alternative definitions under FASM2. I’m trying to keep a single shared include if possible.

Specifically:

Any guidance or best-practice examples would be appreciated.

Thanks,
Michael

27 Feb 2026, 18:54

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8506
Location: Kraków, Poland

Tomasz Grysztar 27 Feb 2026, 23:25

Look no further than in the source of fasmg itself:

Code:

match ,{

        ; fasm 1 detected
        include 'win32a.inc'

} match -,{
else

        ; fasm g detected
        include 'selfhost.inc'

end match
_ equ }

I've been using this trick ever since fasmg started being able to self-host. Some of the fasm2-adapted sources still use it.

27 Feb 2026, 23:25

Ping

Joined: 27 Feb 2026
Posts: 2

Ping 28 Feb 2026, 20:08

Tomasz Grysztar wrote:

Look no further than in the source of fasmg itself:
Code:
match ,{

        ; fasm 1 detected
        include 'win32a.inc'

} match -,{
else

        ; fasm g detected
        include 'selfhost.inc'

end match
_ equ }    
I've been using this trick ever since fasmg started being able to self-host. Some of the fasm2-adapted sources still use it.

Thank you, Tomasz!

28 Feb 2026, 20:08

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