How to use linker

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habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 26 Feb 2009, 21:54

Hi strap89,
I tried to compile fasm\examples\mscoff\mscoff.asm and I can create 'obj' but when I try to link it I have link error:
mscoff.obj : error LNK2001 : unresolved external symbol __imp__MessageBoxA@16
LINK : error LNK2001 : unresolved external symbol __WinMainCRTStartup

I have red the fasm manual but there is no info how to link a coff object

what am I doing wrong?

regards

26 Feb 2009, 21:54

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 26 Feb 2009, 22:28

Quote:

mscoff.obj : error LNK2001 : unresolved external symbol __imp__MessageBoxA@16

You are calling function "MessageBox" from USER32.DLL. For that, you need to link with USER32.LIB file (and usually also KERNEL32.LIB, and other depending on which Win API procs you call). You can find KERNEL32.LIB, USER32.LIB, and others in basically any compiler package, usually MS Visual Studio, Windows Driver Development Kit, or MASM32.

Quote:

LINK : error LNK2001 : unresolved external symbol __WinMainCRTStartup

Microsoft linker by default expects that you are using standard C library (C Runtime, CRT). Because of that, it will look for .LIB file(s) of that library, and also set entry point of your application to that library, where it is called "_WinMainCRTStartup". You can override this behavior by giving "/NODEFAULTLIB" switch to linker.

You may also need to provide "/SUBSYSTEM:WINDOWS" or "/SUBSYSTEM:CONSOLE" switch to compile your app.

26 Feb 2009, 22:28

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 27 Feb 2009, 02:54

It solved "MesageBox" error but not "WinMainCRTStartup"

here are code for make.bat:

Code:

@echo off


\fasm\fasm -s mscoff.fas mscoff.asm mscoff.o
if errorlevel 1 goto errasm

pecvt mscoff.fas mscoff.obj
if errorlevel 1 goto errpecvt

\masm32\BIN\Link.exe  /SUBSYSTEM:WINDOWS /DEBUG /DEBUGTYPE:CV /VERSION:1.0 /INCREMENTAL:YES /NODEFAULTLIB  \Masm32\Lib\USER32.LIB mscoff.obj
if errorlevel 1 goto errlink


goto TheEnd

:errlink
echo _
echo Link error
goto TheEnd

:errasm
echo _
echo Assembly Error
goto TheEnd

:errpecvt
echo _
echo pecvt Error
goto TheEnd

:TheEnd
dir mscoff.*

pause

what is wrong with it?

regards

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27 Feb 2009, 02:54

sinsi

Joined: 10 Aug 2007
Posts: 789
Location: Adelaide

sinsi 27 Feb 2009, 02:59

Try adding "/ENTRY:start" to the link command line (replace "start" with your entry point's label).

27 Feb 2009, 02:59

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 27 Feb 2009, 10:54

Thank sinsi, I tried but than I got error :
LINK : error LNK2001 : unresolved external symbol "_start"

I would like to find a solution for that because I don't believe that Tomasz Grysztar has created the coff format just for fan

If someone ever programmed with fasm coff format please help

regards

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27 Feb 2009, 10:54

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20304
Location: In your JS exploiting you and your system

revolution 27 Feb 2009, 11:07

habran wrote:

LINK : error LNK2001 : unresolved external symbol "_start"

The linker is looking for a label named "_start". So you can do this in your asm file:

Code:

format coff ...
entry _start
public _start

_start:
   ;your code starts here
   invoke ExitProcess,0

27 Feb 2009, 11:07

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 27 Feb 2009, 12:45

Oh yes, I forgot to mention you that when you disable default entry point with /NODEFAULTLIB, you also need to provide another entry point.

27 Feb 2009, 12:45

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 27 Feb 2009, 12:51

Thanks revolution,

now I have assembler error :
entry _start
error: illegal instruction

27 Feb 2009, 12:51

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 27 Feb 2009, 13:00

Thanks vid,
LINK : error LNK2001 : unresolved external symbol "_start"

27 Feb 2009, 13:00

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20304
Location: In your JS exploiting you and your system

revolution 27 Feb 2009, 13:34

habran wrote:

Thanks revolution,

now I have assembler error :
entry _start
error: illegal instruction

Just remove the line. I got confused with the PE format. But you have to use sinsi's suggestion "/ENTRY:start" in the command line.

27 Feb 2009, 13:34

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 27 Feb 2009, 21:55

Still the same error:
LINK : error LNK2001 : unresolved external symbol "_start"

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27 Feb 2009, 21:55

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20304
Location: In your JS exploiting you and your system

revolution 27 Feb 2009, 22:04

habran: I think it is time to post your fasm code. Else this might just keep going around in circles.

27 Feb 2009, 22:04

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 27 Feb 2009, 22:13

revolution here are the code:

Description:		Download
Filename:	MSCOFF.zip
Filesize:	26.26 KB
Downloaded:	615 Time(s)

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27 Feb 2009, 22:13

Yardman

Joined: 12 Apr 2005
Posts: 244
Location: US

Yardman 28 Feb 2009, 05:03

[ Post removed by author. ]

Last edited by Yardman on 04 Apr 2012, 03:26; edited 1 time in total

28 Feb 2009, 05:03

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 28 Feb 2009, 05:31

Yardman, I have got the same result as before
I have no problem to link masm objects, I just want to see any fasm coff objects linked into exe

now I have doubts that it is possible at all to do that

I wish someone prove me wrong

regards

28 Feb 2009, 05:31

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20304
Location: In your JS exploiting you and your system

revolution 28 Feb 2009, 05:36

habran wrote:

Code:

...
\fasm\fasm -s mscoff.fas mscoff.asm mscoff.o
...
pecvt mscoff.fas mscoff.obj
...

Are you trying to make the .fas file into a .obj file?

28 Feb 2009, 05:36

sinsi

Joined: 10 Aug 2007
Posts: 789
Location: Adelaide

sinsi 28 Feb 2009, 07:06

All I did was change "start" to "_start" in 2 places in your .asm file.

Code:

C:\Users\me\Desktop\MSCOFF>\fasm\fasm MSCOFF.ASM
flat assembler  version 1.67.34  (961348 kilobytes memory)
3 passes, 277 bytes.

C:\Users\me\Desktop\MSCOFF>link /subsystem:windows,4.0 /entry:start MSCOFF.OBJ \masm32\lib\user32.lib
Microsoft (R) Incremental Linker Version 6.00.8168
Copyright (C) Microsoft Corp 1992-1998. All rights reserved.


C:\Users\me\Desktop\MSCOFF>dir
 Volume in drive C has no label.
 Volume Serial Number is 0FA6-3849

 Directory of C:\Users\me\Desktop\MSCOFF

28/02/2009  05:28 PM    <DIR>          .
28/02/2009  05:28 PM    <DIR>          ..
27/02/2009  11:32 PM               571 makeit.bat
28/02/2009  05:27 PM               374 MSCOFF.ASM
28/02/2009  05:28 PM            16,384 MSCOFF.exe
28/02/2009  05:28 PM               277 MSCOFF.OBJ
27/02/2009  08:33 AM               925 MSCOFF.wap
15/02/2009  04:48 PM            69,632 pecvt.exe
               6 File(s)         88,163 bytes
               2 Dir(s)  153,521,668,096 bytes free

C:\Users\me\Desktop\MSCOFF>

Why do you use "pecvt"? There's no need afaict.

28 Feb 2009, 07:06

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20304
Location: In your JS exploiting you and your system

revolution 28 Feb 2009, 09:59

sinsi wrote:

All I did was change "start" to "_start" in 2 places in your .asm file.

Why doesn't the fasm board have an icon to show disappointment?

28 Feb 2009, 09:59

habran

Joined: 31 Aug 2008
Posts: 82
Location: South Australia

habran 28 Feb 2009, 10:58

Thanks everyone, I am happy that all of you got involved with this issue,
my goal was to test strap89's "pecvt" to create .obj file from .fas file first and then with linker create .pdb file for debugging with WinDbg, but unfortunately .obj file created this way is 'corrupted' so that linker can't create neither .pdb nor .exe, so if I link .o instead of .obj than it makes .exe and .pdb file but WinDbg doesn't have information about line numbers and can not debug source code

conclusion: pecvt doesn't create proper .obj file
I wish that someone can prove me wrong

regards

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28 Feb 2009, 10:58

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 28 Feb 2009, 13:31

Quote:

conclusion: pecvt doesn't create proper .obj file
I wish that someone can prove me wrong

I quess it would be helpful for strap89 to upload the .obj file, so he can check whether it is really a problem in his tool, or your error.

28 Feb 2009, 13:31

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