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Index > Compiler Internals > Suspicious Weird 16 bit output in FASM 1.68

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_santa



Joined: 15 Dec 2009
Posts: 3
_santa
I tried to compile a simple bootloader using FASM 1.68 in Windows 7 Professional x64. It did not work. The code was ok, and I decided to disassemble the binary. The output was weird. I aksed my friend to compile the same code under Windows XP Professional 32 bit and disassemble it, the output was ok. I think FASM has some troubles with Windows 7 or 64 bit OSes.

Here I attach the source of the bootloader I tried to compile, my disassembler output (Win 7) and my friends disassembler output (WinXP).

Can anyone tell me what's happening??
I will be grateful if someone suggests a solution to fix this.


Description: My fiends disassembled listing of my source, compiled in Windows XP
Download
Filename: WinXP_disasm.txt
Filesize: 11.01 KB
Downloaded: 275 Time(s)

Description: My disassembled listing of my source, compiled in Windows 7 x64
Download
Filename: Win7_disasm.txt
Filesize: 11.04 KB
Downloaded: 268 Time(s)

Description: The source I tried to compile
Download
Filename: source.asm
Filesize: 184 Bytes
Downloaded: 249 Time(s)

Post 15 Dec 2009, 14:29
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17663
Location: In your JS exploiting you and your system
revolution
fasm is a 32bit program so a 64bit OS should have no effect on the output since the OS has to switch to a 32bit mode to run fasm anyway.

Since no one else has reported any such problems perhaps you might want to check your setup for AV interference (or maybe even some malware?). Other than that I can't think of a reason for you to get different outputs.
Post 15 Dec 2009, 14:38
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rCX



Joined: 29 Jul 2007
Posts: 166
Location: Maryland, USA
rCX
I think we'll have to wait for someone with 64-bit OS to test this. Just so everything's clear, it may be a good idea to post the command line used to assemble it and the resulting binary.
Post 16 Dec 2009, 01:52
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Madis731



Joined: 25 Sep 2003
Posts: 2140
Location: Estonia
Madis731
I just tried it on Server 2003 (x64) and I got the WinXP_disasm.txt
I don't have a Win7 installation at hand right now, but I guess that the other listing comes from a different source.
Both FASMW 1.68 and 1.69 result the same binary. It is really odd that the Win7 one omits the "int" and just dumps hex 10 in there. Its like db 0x10 not int 0x10.

Are you *really* sure, its the same source? Smile
Post 16 Dec 2009, 07:21
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_santa



Joined: 15 Dec 2009
Posts: 3
_santa
Answering your questions ...

Madis 731,
Yes, I'm absolutely sure that the source is the same. Recompiled the source 3 more times, the result is the same.

rCX,
I used a batch file to build the source... the command line looks like this: "C:\Program Files (x86)\FASM\fasm.exe" "C:\Users\Alex\Documents\Projects\KERNEL\Sources\boot\bootstrap.asm" "C:\Users\Alex\Documents\Projects\KERNEL\Cd-Rom\boot\bootstrap.bin"

I would appreciate if someone could test it on another windows 7 installation. It would be really nice. Until this i have no idea what causes this strange compilation and how to fix it.

revolution,
I've scanned my pc with AV, no malware nor potentially unwanted software found. The pc is virus-clear.
Post 16 Dec 2009, 15:58
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_santa



Joined: 15 Dec 2009
Posts: 3
_santa
Recent tests showed that problem is only when using the command-line compiler fasm.exe, not fasmw.exe. I think it is a bit not logical coz fasmw.exe is only a front-end to fasm.exe and is not a separate compiler (or maybe I am mistaken), but the facts are that only command line compilers are affected. I tried the older version, fasm 1.64 and got the same odd output as before.

Any ideas how to fix it?
Compiling in fasmw is not a solution for me. Need command line tool.
Post 16 Dec 2009, 16:29
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
I've tried with a Windows 7 and replicating your paths as much as I could (the only difference is that I've used volume F).

Please try exactly what I'm uploading now to be sure we are both testing the same thing. I left a copy of my binary file (Loco.bin) so you can compare differencies.

PS: No, FASMW has the assembler built-in so you could percieve some differences.

PS2: Be sure to execute Make.bat at the very same location I did.


Description:
Download
Filename: Users.zip
Filesize: 2.05 KB
Downloaded: 190 Time(s)

Post 16 Dec 2009, 16:39
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