DLL (need help, thanks)

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ouadji

Joined: 24 Dec 2008
Posts: 1081
Location: Belgium

ouadji 20 Jan 2012, 22:03

hello

,
This code does compile, but does not work
I don't find my mistake ... help ! Crying or Very sad

Code:

format PE GUI 4.0 DLL
entry DllEntryPoint
include 'WIN32a.INC'
section '.code' code readable executable
;-----------------------------------------------------
proc        DllEntryPoint hinstDLL,fdwReason,lpvReserved
                mov     eax,TRUE
            ret
endp 
;-----------------------------------------------------
proc  myF2 varA2:dword
                push    ebx
         mov     ebx,[varA2]
         pop     ebx
         ret
endp
;-----------------------------------------------------
section '.idata' export data readable
export      'my_DLL.dll',myF2,'myF2'
section '.reloc' fixups data discardable

Code:

format PE GUI 4.0
entry start
include 'win32a.inc'
section '.text' code readable executable

start: nop
 int3   ;<---- debugger
   nop
        invoke  myF2,0x1234ABCD
        invoke  ExitProcess,0

section  '.idata' import data readable writeable

library        kernel,'KERNEL32.DLL',\
  my_DLL,'my_DLL.dll'

import     kernel,\
   ExitProcess,'ExitProcess'
import   my_DLL,\
   myF2,'myF2'

_________________
I am not young enough to know everything (Oscar Wilde)-

20 Jan 2012, 22:03

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 20 Jan 2012, 22:23

http://board.flatassembler.net/topic.php?t=13751

Your code should look like this:

Code:

format PE GUI 4.0 DLL
entry DllEntryPoint
include 'WIN32a.INC'
section '.code' code readable executable
;-----------------------------------------------------
proc    DllEntryPoint hinstDLL,fdwReason,lpvReserved
                mov     eax,TRUE
                ret
endp 
;-----------------------------------------------------
proc    myF2 varA2:dword
                push    ebx
                mov     ebx,[varA2]
                pop     ebx
                ret
endp
;-----------------------------------------------------
section '.idata' export data readable
export  'my_DLL.dll',myF2,'myF2'
section '.reloc' data discardable ; revolution's idea

data fixups
        if ~ $-$$
                dd      0,8 ;empty fixups section iff no other fixups
        end if
end data

20 Jan 2012, 22:23

ouadji

Joined: 24 Dec 2008
Posts: 1081
Location: Belgium

ouadji 20 Jan 2012, 22:35

it works ! (thank you loco) Razz

but i don't understand why it works.

why "dd 0,8" ?

_________________
I am not young enough to know everything (Oscar Wilde)-

20 Jan 2012, 22:35

ouadji

Joined: 24 Dec 2008
Posts: 1081
Location: Belgium

ouadji 21 Jan 2012, 00:24

http://board.flatassembler.net/topic.php?p=33087#33087

Quote:

@leo :
... via dd 0,8 it creates valid reloc directory with no real relocs.

@Tomasz Grysztar
You're right, it puts there a dummy block with no actual fixups (haven't noticed that earlier).
If you need such fix, you can just add this dummy entry "dd 0,8" to the fixups data yourself ...

understood.

But why "0,8" and not "0,7" or "x,y" ???

_________________
I am not young enough to know everything (Oscar Wilde)-

21 Jan 2012, 00:24

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 21 Jan 2012, 04:20

Well, if I understood the PE specs correctly, the 8 must be there because it is the size of both dwords. The first number I'm not sure it is actually needed to be exactly 0, but probably would be safer to just use it since it works (and probably Microsoft's compilers do the same thing when no relocations are needed for DLLs).

The "0,8" is the base relocation block header, and it says that zero must be added to the relocation offsets coming next and 8 is the total size of both the header and the relocation entries (none since 8 eight only covers the header itself)

21 Jan 2012, 04:20

Overflowz

Joined: 03 Sep 2010
Posts: 1046

Overflowz 21 Jan 2012, 08:38

EDIT:
sorry, posted mistakely.

21 Jan 2012, 08:38

ouadji

Joined: 24 Dec 2008
Posts: 1081
Location: Belgium

ouadji 21 Jan 2012, 08:58

thank you Loco for this clarification!

_________________
I am not young enough to know everything (Oscar Wilde)-

21 Jan 2012, 08:58

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8357
Location: Kraków, Poland

Tomasz Grysztar 23 Jan 2012, 11:41

That ".reloc" section definition can be shortened this way:

Code:

section '.reloc' data discardable fixups
if ~ $-$$ 
        dd      0,8 ;empty fixups section iff no other fixups 
end if

Using "data fixups" was needed only when no separate ".reloc" section was to be created (to avoid having empty sections, since WinNT loader has problems with them). As in this case section will never be empty anyway (as it is ensured fixups table will not be empty, probably to avoid problems with some Win9x loaders), the shortened variant of declaring separate section for fixups can be used.

23 Jan 2012, 11:41

SFeLi

Joined: 03 Nov 2004
Posts: 138

SFeLi 23 Jan 2012, 12:40

Tomasz Grysztar, btw, is it ok that the following code doesn't trigger an error?

Code:

        virtual
        data fixups ; (any data directory entry actually)
        end data
        end virtual

23 Jan 2012, 12:40

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8357
Location: Kraków, Poland

Tomasz Grysztar 23 Jan 2012, 13:13

No, it is not OK - that is probably a bug.

23 Jan 2012, 13:13

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 27 Jan 2012, 00:17

Tomasz,
This problem is very recurring ultimately. Is there any legitimate reason for using empty relocs? Windows 7 is not accepting empty relocs and this OS is getting more and more popular, so it should be considered if fasm should be adding "dd 0,8" if it detects that the final output will end up with empty relocs (if the user manually added something in the relocs, then fasm should do nothing in that case).

27 Jan 2012, 00:17

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8357
Location: Kraków, Poland

Tomasz Grysztar 27 Jan 2012, 08:34

Windows 7 does accept empty relocations, as any other NT does (I just checked it now on 64-bit Win7 to be sure). It was Windows 9x that had problem with empty relocations directory.

What Windows 7 and other NT-based systems do not accept is an empty section, and the reasons to not include any workaround were discussed here: http://board.flatassembler.net/topic.php?p=33207#33207

We can, however, provide some macro in standard Windows headers, which would generate .reloc section in such a way, that it would work with most of the Windows versions.

27 Jan 2012, 08:34

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 27 Jan 2012, 15:12

Sorry, you're right, I thought I also had problems with data fixups/end data but it actually works.

27 Jan 2012, 15:12

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