Returning values in DLL Functions?

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hansdieter

Joined: 22 Feb 2011
Posts: 5

hansdieter 22 Feb 2011, 00:10

Hello, i'm somewhat new to fasm and trying to make a dll.
the DLL is a plugin for a 64 and 32 bit program, now i made it to compile for 64 bit. But i somewhat don't understand how i can return values in my functions.

Code:

_test db 'This is a test string',0

Code:

proc GetString id,flags
   mov rax,_test ; this will assemble just fine but it somehow doesn't return the string
      ret
endp

The Program requires an LPCTSTR, also: how can i return "UINT"'s in the proc?

22 Feb 2011, 00:10

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 22 Feb 2011, 00:15

The type of LPCTSTR is dependant upon the unicode setting. Your code always returns LPCSTR.

22 Feb 2011, 00:15

hansdieter

Joined: 22 Feb 2011
Posts: 5

hansdieter 22 Feb 2011, 00:19

the program needs:

Code:

LPCTSTR GetString(UINT id, UINT flags)

But with the Proc i posted above, it will not show my _test string, instead it shows some kind of japanese characters.

22 Feb 2011, 00:19

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 22 Feb 2011, 00:21

Is your project unicode?

22 Feb 2011, 00:21

hansdieter

Joined: 22 Feb 2011
Posts: 5

hansdieter 22 Feb 2011, 00:25

Well i don't quite know if the target project is unicode, but here is an example plugin: http://code.google.com/p/rainmeter/source/browse/trunk/Plugins/PluginExample/ExamplePlugin.c

I just want to write a plugin for it, that uses GetString to give a string to the calling progam.

full source:

Code:

;format PE GUI 4.0 DLL ;FOR 32 BIT DLL
format PE64 GUI 4.0 DLL ;FOR 64 BIT DLL
entry DllEntryPoint

include '../INCLUDE/win64a.inc'
;include '../INCLUDE/win32a.inc'

section '.code' code readable writeable executable

_test db 'Test',0
_strTest db 'This is a test string',0
_author db 'test',0
_ver dq 1001d

proc DllEntryPoint hinstDLL,fdwReason,lpvReserved
 sub rsp,8*5
 mov     rax,TRUE
    ret
endp

; VOID Initialize(HWND instance,DWORD iniFile,DWORD section,DWORD ID);

proc Initialize hWnd,iniFile,section,id
    invoke  MessageBox,0,_test,NULL,MB_OK
       mov rax,0
   ret
endp

; DWORD Update(DWORD id);

proc Update id
  ;local buffer:DWORD
     ;lea eax,[buffer]
   ;invoke MessageBox,0,_test,NULL,MB_OK
       mov eax,0
   ret
endp

; DWORD GetString(UINT id, UINT flags);
proc GetString id,flags
       mov rax,_test
       ret
endp

; DWORD GetPluginVersion();
proc GetPluginVersion
     mov rax,_ver
        ret
endp

; DWORD GetPluginAuthor();
proc GetPluginAuthor
       lea eax, [_author]
  lea rax, [_author]
  ;mov eax,_author
    ret
endp

; VOID Finalize();
proc Finalize instance,id
  mov rax,TRUE
        ret
endp

section '.idata' import data readable writeable

  library user,'USER32.DLL'

  import user,\
    MessageBox,'MessageBoxA'

section '.edata' export data readable

  export 'TEST.DLL',\
   Initialize,'Initialize',\
        Finalize,'Finalize',\
    Update,'Update',\
        GetString,'GetString',\
  GetPluginAuthor,'GetPluginAuthor',\
      GetPluginVersion,'GetPluginVersion'

section '.reloc' fixups data discardable

22 Feb 2011, 00:25

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 22 Feb 2011, 00:28

hansdieter wrote:

Well i don't quite know if the target project is unicode ...

If you are returning strings then you will have to find out if your project is unicode. You can't return ASCII strings in a unicode project. And you can't return unicode strings in an ASCII project. LPCTSTR changes its type based upon the project setting.

22 Feb 2011, 00:28

hansdieter

Joined: 22 Feb 2011
Posts: 5

hansdieter 22 Feb 2011, 00:30

Ok, yes it seems to be unicode.

22 Feb 2011, 00:30

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 22 Feb 2011, 00:31

http://msdn.microsoft.com/en-us/library/aa383751%28v=vs.85%29.aspx:

Code:

#ifdef UNICODE
 typedef LPCWSTR LPCTSTR; 
#else
 typedef LPCSTR LPCTSTR;
#endif

22 Feb 2011, 00:31

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20340
Location: In your JS exploiting you and your system

revolution 22 Feb 2011, 00:32

hansdieter wrote:

Ok, yes it seems to be unicode.

Then do this:

Code:

_test du 'This is a test string',0

22 Feb 2011, 00:32

hansdieter

Joined: 22 Feb 2011
Posts: 5

hansdieter 22 Feb 2011, 00:34

It works! Thank you very much. Your help is much appreciated!

22 Feb 2011, 00:34

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