fasm 2 as a set of scripts and headers for fasmg

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vityacv

Joined: 27 Oct 2012
Posts: 15

vityacv 20 Aug 2025, 18:56

Having issue with this sample on FASM 2 - Custom error: operand sizes do not match.

Code:

include 'win64w.inc'
format pe64

struct Test2
a1 rd 1
ends

struct Test3
a1 rd 1
a2 rd 1
a3 rd 1
a4 rd 1
a5 rd 1
ends

struct Test1
a1 rd 1
a2 Test2
a3 Test3
ends

struct Test4
a1 rd 1
a2 rd 1
ends

virtual at 0
V1 Test4
V2 Test4
end virtual

mov esi,[rax+rax+Test1.a3+V1.a1]
ret

FASM 1 compiles without error

20 Aug 2025, 18:56

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8528
Location: Kraków, Poland

Tomasz Grysztar 20 Aug 2025, 19:11

vityacv wrote:

Having issue with this sample on FASM 2 - Custom error: operand sizes do not match.

Code:

include 'win64w.inc'
format pe64

struct Test2
a1 rd 1
ends

struct Test3
a1 rd 1
a2 rd 1
a3 rd 1
a4 rd 1
a5 rd 1
ends

struct Test1
a1 rd 1
a2 Test2
a3 Test3
ends

struct Test4
a1 rd 1
a2 rd 1
ends

virtual at 0
V1 Test4
V2 Test4
end virtual

mov esi,[rax+rax+Test1.a3+V1.a1]
ret

FASM 1 compiles without error

The "Test1.a3" has associated size (20 bytes), as the STRUCT macro in fasm2 has an added feature of sizing all these labels properly. This was missing in fasm's implementation, because it was not really possible to implement there except for a small set of supported sizes.

If you'd prefer to not have this feature, comment out the portion of "instantiate" macro:

Code:

                arrange tmp, =label instance; : sname.=__size__

Another workaround is to rearrange the expression so that the intended size comes first.

20 Aug 2025, 19:11

vityacv

Joined: 27 Oct 2012
Posts: 15

vityacv 04 Dec 2025, 17:24

Code:

format binary
use64

ret
align 16

flat assembler  version g.l04h
1 pass, 1 byte.

Getting 1 byte output instead of 16, fasm 1 have same result. Also fasm 1 creates output file with .bin extension, should fasm 2 do the same?

04 Dec 2025, 17:24

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8528
Location: Kraków, Poland

Tomasz Grysztar 04 Dec 2025, 18:13

vityacv wrote:

Getting 1 byte output instead of 16, fasm 1 have same result.

It's compatible then, isn't it?

But with fasm2 you can also do this:

Code:

align 16, 90h

See the comments in the package.

vityacv wrote:

Also fasm 1 creates output file with .bin extension, should fasm 2 do the same?

This small difference is actually handy when testing one against the other. Of course adding a simple AS in the headers could bridge this gap, too.

04 Dec 2025, 18:13

vityacv

Joined: 27 Oct 2012
Posts: 15

vityacv 22 Apr 2026, 15:46

With this sample and triggering build without the 32.ico in folder

Code:

format pe64
entry Main

include 'win64w.inc'
include 'encoding\utf8.inc'

Main:
ret

align 8
test1 du '1111111111111111111111111111111',0

align 8
data fixups
end data

align 8
data resource
directory RT_ICON,icons,RT_GROUP_ICON,group_icons
resource icons,32,LANG_NEUTRAL,icon_32
resource group_icons,1,LANG_NEUTRAL,main_icon
icon main_icon,icon_32,'32.ico'
end data

Getting:

Quote:

flat assembler version g.l4gs
Error: not enough memory to complete the assembly.

It also can freeze when executed multiple times.

22 Apr 2026, 15:46

bitRAKE

Joined: 21 Jul 2003
Posts: 4444
Location: vpcmpistri

bitRAKE 22 Apr 2026, 20:38

Code:

> fasm2 -v 2 -e 5 vityacv.error.asm
flat assembler  version g.l2fx
flat assembler  version g.l5p0

vityacv.error.asm [23]:
        icon main_icon,icon_32,'32.ico'
macro icon [4]:
        file icon_file:6,16
Processed: file '32.ico':6,16
Error: source file '32.ico' not found.
vityacv.error.asm [23]:
        icon main_icon,icon_32,'32.ico'
macro icon [9]:
        data#% file icon_file:position,size
Processed: data#1 file '32.ico':position,size
Error: source file '32.ico' not found.
vityacv.error.asm [23]:
        icon main_icon,icon_32,'32.ico'
macro icon [16]:
        file icon_file:6,12
Processed: file '32.ico':6,12
Error: source file '32.ico' not found.

... is what I'm getting with a couple versions. (Just updated?)
(Of course, it builds with icon file.)

_________________
¯\(°_o)/¯ AI may [not] have aided with the above reply.

22 Apr 2026, 20:38

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8528
Location: Kraków, Poland

Tomasz Grysztar 23 Apr 2026, 08:29

bitRAKE wrote:

... is what I'm getting with a couple versions. (Just updated?)

The issue was non-deterministic. The FILE directive did not zero the memory reserved for data from file, and .ICO parser was LOAD-ing a length field from there. It was then allocating the memory for icon data with a "random" size.

In particular, if you've been testing both the new version (which clears the reserved block) and the old one, the old might have been reusing a zeroed block, masking the problem.

23 Apr 2026, 08:29

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