Question about DLL linking... (newbie ;))

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denial

Joined: 12 Sep 2004
Posts: 98

denial 13 Sep 2004, 12:46

Hello,

at the moment I'm trying to link a Visual C++ DLL into a Windows-Console FASM Application... I read through the PEDLL example that comes with FASM, however I did not understand everything. Is there a tutorial or something out?

My general questions I got:

- I saw in the example that the parameters for the linked functions (MessageBox,...) get pushed onto the stack. I was wondering how that exactly works and how the used function knows where to take them?

- What does these lines mean?

Code:

  dd RVA dlldemo_table,0,0,RVA dlldemo_name,RVA dlldemo_table
  dd 0,0,0,RVA kernel_name,RVA kernel_table
  dd 0,0,0,0,0

I can see that a double-word gets declared but I don't know what RVA means...
And what's about the last line? Looks strange to me Wink

It would be nice if you could help me.
thank you Smile

[/code]

13 Sep 2004, 12:46

decard

Joined: 11 Sep 2003
Posts: 1092
Location: Poland

decard 13 Sep 2004, 14:54

Hi denial,
In PEDLL import section is just simply built manually. You simply don't need to understand what are those zeroes Smile

Try this example:

Code:

format PE DLL
entry DLLEntryPoint

include "%fasminc%/win32a.inc"

; data section
section '.data' data readable writeable

szTitle db "DLL example", 0
szText  db "Hello form DLL!", 0


; code section
section '.code' code readable executable

proc DLLEntryPoint, hinstDLL,fdwReason,lpvReserved
 enter
       mov     eax,1
       return
endp


proc Hello
        enter
       invoke  MessageBox, HWND_DESKTOP,szText,szTitle,MB_OK+MB_ICONINFORMATION
    return
endp

; imports
section '.idata' import data readable
library user32,"USER32.DLL"

import user32,\
       MessageBox,"MessageBoxA"

; exports
section '.edata' export data readable

export "SIMPLEDLL.DLL",\
       Hello,"Hello"

; fixup section - needed in DLL
section '.reloc' fixups data discardable

13 Sep 2004, 14:54

denial

Joined: 12 Sep 2004
Posts: 98

denial 13 Sep 2004, 15:10

Thank you for your answer,
but if I'm not confused about your example now, I think you got me wrong Wink

This is an example how to write a DLL in FASM isn't it? What I need is more information about use a DLL in FASM written in another language, Visual C++ for example.
Maybe you or somebody help can help me?

13 Sep 2004, 15:10

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 13 Sep 2004, 15:20

You can import functions from any dll, exactly the way you do it for Windows system dll's (user32.dll for example). You have to create import section (or "data import..." block in any other section and write there the libraryes and functions you want to import. See the syntax of "library" and "import" macroses (include/macro/import.inc file), they are pretty clear (IMHO).
Don't be afraid to import all functions from the DLL in one block (better create one big .inc file for the whole DLL) - FASM will include in import data only the functions you use in your program. See for example the include files for Windows system dll's: include/apia/user32.inc

Regards.

P.S. Of course you can load dll's dynamicaly using Windows API functions: LoadLibrary, LoadLibraryEx, GetProcAddress, FreeLibrary. Read Win32 API guide for details.

13 Sep 2004, 15:20

denial

Joined: 12 Sep 2004
Posts: 98

denial 13 Sep 2004, 16:21

Thank you

Could you explain the parameters for these two macros (import, library)?

macro library [name,string]
name is of course the file, but what is string?

macro import name,[label,string]
name is here the name of the function... What is label and string for?

Thank you again Wink

13 Sep 2004, 16:21

decard

Joined: 11 Sep 2003
Posts: 1092
Location: Poland

decard 13 Sep 2004, 16:33

see an example:

Code:

library kernel32,"KERNEL32.DLL"

name (kernel32) is just some name (that will be used with import macro) and "string" is actual DLL file name.

Code:

import kernel32,\
ExitProcess,"ExitProcess"

with import macro we specify which functions to load from a DLL. In this case we import ExitProcess from kernel32.dll. "name" is the same name that you specified as first parameter of library macro. Then "label" is a name that you will refer to when calling given function; and finally "string" is a function name in a DLL.

Hope my description was clear enough Smile

13 Sep 2004, 16:33

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 13 Sep 2004, 17:34

Code:

; In you import section

; Also, you can specify more than one library:
library  library1, 'mylib1.dll', library2, 'yourlib2.dll'

;... or better (more readable):
library  library1, 'mylib1.dll',  \
         library2, 'yourlib2.dll'

;...and more that one function per "import" statement...
import library1,    \
       Function1, 'SomeFunctionName',  \
       Function2, 'SomeOtherFunction',  \
       TheBestFunc, 'SlowCPPFunc'
; Note - it is not obligatory to use the same names for functions as they are defined in the dll.

; In your code section

; call these functions this way:

    invoke  Function1, arg1, arg2  ; macro "invoke"
; or:
    stdcall   [Function2], arg1, arg2  ; macro "stdcall" with indirect addressing.
; or even:
    push arg2
    push arg1
    call  [TheBestFunc]  ; instruction "call"

Regards

13 Sep 2004, 17:34

denial

Joined: 12 Sep 2004
Posts: 98

denial 13 Sep 2004, 17:43

Thank you very, very much for your help... Now I understood everything. Smile

It's a great bord here - the support is fast and friendly. Smile

Regards
denial

13 Sep 2004, 17:43

denial

Joined: 12 Sep 2004
Posts: 98

denial 13 Sep 2004, 18:38

Oh I got one more problem I posted but I solved it myself now. Thank you.

13 Sep 2004, 18:38

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