!!!SOLVED!!!: Follow up question on stackoverflow: how can i get the dos exe build from segments in multiple asm files binary identical to the single asm file version
UPDATE 0: solved the external problem but i've got a problem with setting the data segment, see UPDATES
(also posted this question on: https://www.reddit.com/r/asm/comments/d33mpn/masm_x86_16bit_dos_exe_how_to_split_single_asm/)
im working on an tool that helps binary identical reassembling of DOS 16bit, IDA Pro asm output, for that im using an "well defined" input exe based on this asm-code (its my playground for serveral hard to reverse features, strongly cutted for this question)
[all_in_one.asm]
.model medium
.386
seg000 segment use16
text db 'Hello World!',0ah,0dh,'$'
seg000 ends
seg001 segment use16
;assume cs:seg001 ; for TASM
start proc
mov ax,seg seg000
mov ds,ax
push ax
pop ax
call print
mov ax,4c00h
int 21h
start endp
seg001 ends
seg002 segment use16
;assume cs:seg002 ; for TASM
print proc far
mov dx,offset text
mov ah,09h
int 21h
retf
print endp
seg002 ends
seg003 segment stack use16
db 256 dup (?)
seg003 ends
end start
im not using .STACK or other features of MASM intentional because normal reversed results of IDA are full of special cases (multiple stacks, segment ordering etc.) that i want to replicate 1:1, im not interested in how to write the same shorter in MASM, just the exact result is relevant for me
i can build the above code using
[build.cmd]
:: MASM x86, 14.16.27032.1 from VS2017 Community (current UASM, TASM also work)
ml.exe /c /omf all_in_one.asm
:: UniLink v1.11 [beta] (build 11.23), ftp://ftp.styx.cabel.net/pub/UniLink/
ulink.exe all_in_one.obj
:: Microsoft Linker 16bit, Version 5.60.339 Dec 5 1994
link.exe all_in_one.obj,,,,,
and create a fully working 16 bit dos executable (tested with IDA and Dosbox) with both linkers (should also work with TLink, WLink, Optlink and Alink and all other available linkers that support 16bit dos executables)
everything is fine... but
reversed executables tends to have huge segments and sometimes 20 or even over 100 of them, so my tool split the segments into single files, it easier to get the single segment files to be binary comptible with the original if not everything is clutched together
so i splitted the file into segment files (and inc-files for forward declaration, maybe there is a better way with MASM for that - the forward declared data should be type safe as possible, i've read about EXTERNDEF and others but i have no idea what are the pros/cons of using it)
[seg000.asm]
.model medium
.386
seg000 segment use16
text db 'Hello World!',0ah,0dh,'$'
seg000 ends
end
[seg000.inc]
seg000 segment use16
extern text:far
seg000 ends
[seg001.asm]
.model medium
.386
; forward declare segments
include seg000.inc
include seg002.inc
seg001 segment use16
start proc
mov ax,seg seg000
mov ds,ax
push ax
pop ax
call print
mov ax,4c00h
int 21h
start endp
seg001 ends
end start
[seg002.asm]
.model medium
.386
; forward declare segments
include seg000.inc
seg002 segment use16
print proc far
mov dx,offset text
mov ah,09h
int 21h
retf
print endp
seg002 ends
end
[seg002.inc]
seg002 segment use16
extrn print:far
seg002 ends
[seg003.asm]
.model medium
.386
seg003 segment stack use16
db 256 dup (?)
seg003 ends
end
and try to build it with
[build_multiple.cmd]
ml.exe /c /omf seg000.asm
ml.exe /c /omf seg001.asm
ml.exe /c /omf seg002.asm
ml.exe /c /omf seg003.asm
ulink.exe seg000.obj seg001.obj seg002.obj seg003.obj
link.exe seg000.obj seg001.obj seg002.obj seg003.obj,,,,,
the assembling works for all asm files, but both linkers return errors
UniLink v1.11 [beta] (build 11.23)
Error: Unresolved external 'text' referenced from 'seg001.obj'
Microsoft (R) Segmented Executable Linker Version 5.60.339 Dec 5 1994
Copyright (C) Microsoft Corp 1984-1993. All rights reserved.
seg002.obj(seg002.asm) : error L2029: 'text' : unresolved external
seg001.obj(seg001.asm) : error L2029: 'text' : unresolved external
is my forward declaring of the segment content correct? any idea how to fix the unresolved external linker error?
UPDATE 1: unresolved external fixed with public
i change my data segment to:
seg000 segment use16
public text ; <====
text db 'Hello World!',0ah,0dh,'$'
seg000 ends
now it links but something seems to be not correct with my stack segment
UniLink v1.11 [beta] (build 11.23)
Error: SP value out of range
Error: SS value out of range
the Microsoft Linker does not print any error but the resulting exe prints just garbage
UPDATE 2:
the all_in_one and splitted-segments exe are binary(with header) identical except one byte
the mov ax,seg dseg in seg001 is encoded different
[all_in_one exe]
B8 (00) 10 --> mov ax, 0x1000 <-- 0x1000 is seg000(data)
[splitted exe]
B8 (01) 10 --> mov ax, 0x1001 <-- 0x1000 is seg001(code)
that means instead of seg000 splitted exe uses seg001 as the data segment (my first code segment) and then tries to print something from the code-segment until there is a '$' found in ram
why is that happening?
my idea so far is:
im including this seg000.inc (literaly empty segment only for forwarding and extern) right before the definition of seg001, could it be that the assembler thinks the included empty segment is exactly there and can be used, and because of its size of 0 its equal segment as seg001?
if that is the reason - how do i forward my procs and values then?
